Tour to Neocene
|
||||||||||||
During the second half of Cenozoic era Antarctica has turned
to icy continent almost lack any terrestrial life. Only in some places there
were “oases” – land areas lack of ice. In such places mosses and lichens and
in some places even grasses grew. From among animals in such places there were
only tiny insects. In Neocene, when the climate began warmer, the surface of
continent began releasing from an ice shield. On the ground thickets of mosses
and lichens gradually appeared, and there insects settled – the descendants
of ones have got to the continent with winds from Africa and South America.
In addition to them on deserted coast of the continent birds had began to fly
and to bring even more seeds of grasses on their paws and feathers. Edges of
the continent in Neocene became free from ice, and now the wide grassy steppe
with some areas of dense cushion bushes was stretched there. Only the borders
of glaciers still have the rests of initial flora of Antarctica – a belt of
moss bogs.
In winter there is still cold in Antarctica, and there is a polar night. But
in the summer the sun shines all day and night, and for some weeks a year the
weather happens rather hot.
In the center of Antarctica glaciers have not thawn yet, and many rivers originate
at the Central Antarctic Glacier. In summer ice begins thawing gradually, and
water accumulating on the surface of a glacier in extensive lakes searches for
a way out. Usually any edge of a glacier does not maintain its pressure, and
water washes a deep gully, flowing down on slopes of glacier.
At the way of thawed snow from a glacier the zone of peat moss bogs is stretched.
Sphagnum moss has a unique moisture capacity, and in spring bogs literally inflate
like sponge, and then gradually give the stored water to numerous streams. Flowing
through peat bogs, water is additionally cleared of dust and suspension and
turns more acidic.
Sphagnum bogs of Antarctica represent the residence of the most ancient settlers
of the continent in postglacial epoch. Here there is an original microclimate,
an echo of the past epoch: close glaciers freeze ground, and from them the cold
wind frequently blows. Therefore local inhabitants live either in the slowed
down rate, or in maximal degree use short serene days. Since early spring, when
the sun warms enough, some moss cushions show the appreciable movement inside
them. There thick grubs with translucent body covers – posterity of the large
moss leaf beetle – wriggle
and eat leaflets of sphagnum. They have fine appetite, and after their feeding
on the surface of moss appreciable bald patches arise. Grubs of moss leaf beetle
hide among moss plants, staying between their stalks. Only the head of grub,
gnawing obstinately fluffy heads of moss, is visible from outside. When above
bogs any casual bird flies by, grubs, as if on command, hide deeply in moss.
It is their usual reaction to large and quickly moving objects. They do not
distinguish colors and small details with their small eyes, and can see contours
of the objects only. The main task of these grubs is to eat well. Grubs of early
clutches may turn to adult beetles this summer.
In addition to moss leaf beetles at the bogs many other insects feed. But some
of them will be noticed hardly even by sharp-sighted bird. Myriads of tiniest
springtail insects skip on surface of moss, and even of water. They live in
the world where the gravity is not of great importance, but other forces are
felt much keener, than in a macrocosm. The surface tension film supports them,
as if elastic trampoline - they are too easy to break through it. Springtails
are among native inhabitants of Antarctica which have survived in Cenozoic glaciation
of the continent. Some species live even on the surface of glacier where they
feed on algae developing on snow and in pools of melt water, and also on insects
blown here by wind.
Bogs seem stagnant only at first sight. Actually water is constantly freshened,
especially in the summer, when the Central Antarctic Glacier melts. Water from
bogs around gradually filters and gathers to numerous streams murmuring at the
meadows of Antarctica and merging gradually to larger rivers.
Antarctic streams are remarkable in cold and clean water. This is a favorable
place for breeding of smaller Diptera species. Larvae of diverse midges stick
like a live carpet on all places suitable for their life in the slightest degree:
the surface of stones and plants. Larvae attach to stones using the viscous
liquid stiffening like glue. Having attached in suitable place, larva stretches
its antennae in stream of water to catch various edible things. Plumose antennae
work as a sieve, catch the vegetative rests and the protozoans carried by water.
From time to time they are turned to the larva’s mouth and it eats the caught
animals. In absence of the majority of enemies, first of all of fresh-water
fishes, midges and mosquitoes of Antarctica prosper. But dipterans do not stand
at the top of food pyramid: they nevertheless have enemies even in this isolated
world.
From under flat pebble even flatter live being appears. This strange creature
is kept in strong current, seizing by legs in the smallest asperities of the
stone. To fix additionally in current the suckers developed on legs help it.
And moreover the body shape also represents a sample of technical perfection:
current literally presses strange creature to the bottom instead of breaking
it out and carrying away. But all the same the small monster is very cautious:
it moves its legs one by one, and five legs from six always seize a stone. Frightening
head with large spherical eyes and the triangles of underdeveloped wings stretched
along its back clearly show an origin of this creature: it is a nymph of dragonfly
– one of numerous species of these insects inhabiting Antarctica of Neocene
epoch. Adult individuals of this species swoop above the stream, sparkling with
blue metallic shining abdomens. The abdomen shape of an adult dragonfly almost
does not change, hence the name of this insect: flattened stream dragonfly.
Midge larvae stand at the bottom level of food pyramid in stream: they serve
as food for this nymph. Flattened stream dragonfly nymph scrapes them off with
its wide mask (lower lip), as if by shovel. It as if grazes on the underwater
meadow, tearing off from stones larvae of midges, flies and mosquitoes which
can’t or simply have not time to escape from it. But sometimes it is necessary
for the nymph of flattened stream dragonfly itself to show quickness and care.
From time to time stream is visited by larger predators, local birds, for which
flattened stream dragonfly nymph is simply an easy snack.
Falcon grackle, one
of zoophagous birds of Antarctica, frequently flies to the stream in searches
of food: it is possible to find a lot of meal here if to attempt. The bird knows
how to get midge larvae. It overturns pebbles and pulls them out from water,
stacking one on another, and then quietly pecks off midge larvae attached to
it, which can’t escape in flight. From time to time the feathery predator sneezes,
when water gets to its nostrils while it takes the next pebble from water. But
midge larvae represent no more than snack, and the bird searches for more essential
prey. Nymph of flattened stream dragonfly will fit for dinner to falcon grackle
quite good, but it is more difficult to catch it. While grackle is rummaging
somewhere aside, nymph eats, not paying attention to it. But at first signs
of danger, when the bird has stepped in its side, nymph had promptly squeezed
deep between stones. With its sharp-sighted eyes the predatory bird notices
the movement among stones and begins the pursuit of dragonfly nymph. It overturns
small stones, trying to find nymph, but it is simply dug in gravel. If the falcon
grackle would be more persevering, it would catch the nymph. But the bird has
a great disadvantage: water gets to its nostrils, and the bird sneezes for a
long time. The effect of suddenness is lost, hunting has not gone right obviously,
and falcon freckle flies out soon. When the situation had quieted down, midge
larvae turned to lumps began to straighten antennae on the sly, and a bit later
gravel at the stream bottom has begun to move, and from its shelter dragonfly
nymph creeps out. Having convinced that everything is quiet around, it has continued
scraping stones.
Falcon grackle is more an “amateur fisher” – it incidentally searches for food
in rivers and only diversifies its menu with insects. But the bird which has
mastered underwater feeding is found in bogs of Antarctica. Necktied
mousebird, tiny flightless passerine bird, accurately moves down under water,
clinging by claws against the stems. Before diving it carefully greases plumage
with secretions of preen gland to prevent getting wet. Therefore when this bird
appears under water, its plumage becomes silvery from the thinnest layer of
air which is kept on its surface. Nostrils of mousebird at diving are closed
by small leathery lids, and the bird feels like perfectly under water. Having
gone down to the stream bottom, it hasty rummages around stones, pecking off
midge larvae. Feeling that the stock of air comes to an end, mousebird simply
unclenches its toes, emerging on surface of water, as if a cork. Due to greasing
the plumage appears dry, and the bird does not soak through and does not feel
cold. Within the year it continues hunting under water until streams will cover
with ice.
Having caught its breath, necktied mousebird dives once again. And at once it
notices under water the nymph of flattened stream dragonfly, which unperturbably
scrapes midge larvae from stones. This prey costs the works on its capture,
and the tiny bird rushed on it like a cat on the mouse. Having torn off the
nymph from stones, mousebird emerges on surface of water, leaves from the stream
and begins banging the dragonfly nymph furiously against small stone. When the
movements of insect had stopped, mousebird had pressed it by paw and began tearing
off pieces of it with powerful beak, greedy swallowing them. In some minutes
from dragonfly nymph only frightening head and the rests of legs remain. Having
finished the meal, the bird has disappeared in thickets.
Antarctic streams gradually merge to small rivulets, and they are united to
wide rivers meandering on plain. For freshwater fishes sea open spaces represent
as absolute obstacle, as the highest mountain ridges or waterless desert, therefore
the rivers of Antarctica completely lack of freshwater fishes. Only occasionally
marine fishes come to rivers mouths to get rid of parasites irritating them.
But they also do not remain here for a long time. But in fresh waters of this
continent aquatic insects have found the new homeland. These creatures had easily
overcome hundreds of kilometers above the ocean, and colonized the continent.
Dragonflies have especially succeeded in development of Antarctica.
In thickness of water numerous long-bodied creatures swim. At first sight it
seems that in water shoals of fry of various fishes teem. But at closer look
it appears, that each of such “fishes” has short antennae and six legs which
nestle against its sides during the swimming. These are nymphs of one of the
most surprising insects of Antarctica, of stripe-tailed insectfish. Their gills
growing on the tip of abdomen are colored black and white, helping these nymphs
to distinguish each other at the great distance and to unite to schools for
protection against enemies. These creatures behave like fishes in many respects:
they gather in many thousands schools and swim together, coordinating their
movements. But here it is not only external similarity: eating tiny plankton
worms and crustaceans, they occupy an ecological niche of small fishes. Diverse
species of insectfishes substitute various fishes that became possible because
of absence of competition to fishes in Antarctica.
But fishes are different, and there are predators among them. And among their
Antarctic six-legged analogues also there are the creatures which are not making
a concession in ferocity to fishes of other continents (certainly, with the
correction for their size).
Striped greenish nymph about 10 cm long traps small insectfish nymphs under
leaves of cane floating on surface of river backwater. It is a nymph of the
species related to stripe-tailed insectfishes – of voracious insectfish. Waiting
for an opportunity to attack small animals, it hangs for hours under the stalk
of floating plant, having hooked for it with one leg. Huge spherical eyes look
for any small creatures scurrying in water. Nymph does not pay attention to
the tiniest worms and small mosquito larvae which swim fast beside it and even
hit on the hidden nymph. But it waits for more essential prey.
And after any time its expectation appear justified: in thickness of water small
school of little insectfish larvae swims, looking like fry of any fishes. It
is a favourite prey of monstrous nymph. Striate nymph, like a river perch, makes
a prompt rush. Having stretched the gills growing on its abdomen tip like a
tail fin, it swims promptly, bending its body like a fish. The rush is short,
but it brings quite good result: striate nymph catches up the school of small
insectfishes. Having overtaken with escaping nymphs of stripe-tailed insectfish,
the predator opens long narrow mask, and puts with it an exact short impact
to one of pursued nymphs. Palps pressed to each other easily punch covers of
the nymph and it perishes, being stubbed on the tip of predator’s mask. Having
taken its prey with mandibles, nymph of voracious insectfish returns to its
shelter, wriggling in water lazily. Having clung to floating stalk, it begins
devouring of caught smaller nymph, from which only legs and piece of completely
eaten out abdomen remain only.
Somewhere nearby under floating leaves of plants other nymphs of the same species
hide. They prefer to keep at the distance from their congeners: it is not known
who you would be after fight with them – the winner or its prize.
Not all nymphs of Antarctic dragonflies are furious predators. Swimming in backwaters,
stripe-tailed insectfish nymphs frequently meet unusual creatures soaring lazily
in thickness of water. These creatures are also damselfly nymphs, but the way
of their feeding is unusual. They do not hunt for their relatives, but scoop
various aquatic critters with their masks covered with bristles: rotifers and
other worms, small mosquito larvae and large infusorians. These are nymphs of
“queen of hearts”, one of the brightest and the most beautiful damselflies of
this continent. They soar in thickness of water, having stretched in sides their
long legs covered with hairs. Small nymphs of insectfish instinctively bypass
them, keeping the safe distance, though these creatures are not dangerous to
them. They do not pay attention to small insectfish nymphs, eating the smallest
fraction of plankton. In quiet water of river bays and oxbows where algae develop
plentifully and water teems with tiny plankton organisms, such nymphs live in
dozens. Despite of the calmness, such nymph can swim very quickly in case of
danger.
The world of dragonfly and damselfly nymphs inhabiting any reservoir is the
world of carnivorous creatures. To eat another one or to become eaten – it is
a usual business for these insects. And in this severe rule the contribution
is brought by creatures from another world, by local birds.
Intrusion into the world of dragonfly nymphs always occurs from above and passes
in almost the same way. When the school of insectfish nymphs appears too close
to the surface of water, it draws attention of small long-winged bird with deeply
forked tail. It is not an Antarctic swallow-looker, an inhabitant of meadows:
the bird has white color with black “cap”, and instead of short rostel is armed
with rather impressive bill. It is a halcyon tern, the usual summer inhabitant
of rivers of Antarctica.
Having noticed a school of stripe-tailed insectfish nymphs, it begins hunting.
Having cut water surface by lower jaw, this bird snatches out one nymph from
school, soars up, makes a turn and skims over water surface again. Its relatives
fly nearby. Having noticed that their congener stays for too long time at the
same place, they also decide to try their luck there. After some seconds above
backwater small, but noisy flock of halcyon terns is formed. They gradually
drive school of insectfish nymphs to riverbank and arrange hazardous hunting
for them. But nymphs are not going to surrender to be eaten by birds: their
school scatters and nymphs try to leave to the bottom and to hide in thickets
of underwater plants. But even here they are unable to find rest: halcyon tern
dives perfectly, and some birds immediately direct after escaping stripe-tailed
insectfish nymphs. Though why do they need to chase small and resourceful prey,
when there is something more essential near them? Large nymph of voracious insectfish
was disturbed by dived birds, and now searches for rescue, trying to swim away.
But it would be better for it to nestle against floating plants, creeping inside
deeper: halcyon terns swim faster than it can, and the destiny of a predator
is solved – one of birds eats this nymph.
When hunting of halcyon terns comes to end, dragonfly and damselfly nymphs may
continue their habitual life. They live in water till one or two years for flashing
their bright colors for some weeks or only some days in the summer, flying above
a native reservoir and moving their iridescent wings. And for the sake of this
holiday of colors every nymph reached the proper age should pass the transformation.
Insectfish nymphs gather to schools of about the same age and the size that
allows them not to be afraid of their own larger congeners. Adult insectfish
nymphs, having reached the maximum size, begin preparing to metamorphosis. Shoals
of many thousands of them swim up to coastal reeds, and nymphs as if recollect
that they have legs. Not paying attention against each other, they creep out
on plants. Before this moment they used legs, perhaps, only to leave an egg
shell and to live for few days in aquatic moss thickets. Nymphs creep, clumsily
moving their legs and trying to climb upper. Having chosen suitable place according
the signs known to them only, insectfish nymphs begin moulting quickly. At this
moment they are absolutely motionless and defenseless against numerous predators.
They are safe from dragonflies of other species, because dragonflies catch other
insects mostly in flight, not paying attention to ones perching on leaves. But
birds have more flexible behaviour, and they study easily. Halcyon tern involved
with an abundance of meal, which as if is asked for getting into the beak, hovers
in air and catches these nymphs one by one. But all the same there is greater
number of insectfish nymphs, than these birds can eat, and the significant part
of them is hidden in thick of canes where long-winged bird can’t fly. Therefore
terns do not succeed to put significant damage to moulting insectfish nymphs.
Besides under water there is immeasurably larger number of new nymphs not ready
to a metamorphosis yet than has got out on plants this day. The flight of insectfishes
is dragged on almost whole summer, and each time metamorphosis would be undergone
only by small part of the total population of these insects.
For some time insectfish nymphs stay motionless, and only pulsing movements
of their abdomens give out the signs of life. But gradually attributes of the
future changes become distinct. At first thoracal segments of nymph crack on
its back with longitudinal seam. Then from seam wet and shiny body of the future
dragonfly appears. Abdomen extends and, as if a spring, pushes young dragonfly
out from exuvia which became too close to it. The young dragonfly at first sticks
out from exuvia, keeping in it with abdomen tip, and then is bent and clings
against the stem by legs. The wings, at first wrinkled and soft, begin smooth
out, then harden and soon the damselfly is ready to flight. Windflaws blow from
reeds the handfuls of empty exuviae, gathering them in small heaps floating
on surfaces of lakes and river backwaters.
Insectfish imagoes migrate to upper courses of rivers where midges and mosquitoes
breed plentifully. Mayflies and caddisflies have not reach Antarctica – ocean
passages are too wide for these insects living for very short time as flying
stage. Therefore at this continent insectfishes replace them. These numerous
insects gather in numerous swarms and hover above water. Their winged adult
life is very short; therefore they at once arrange courtship flights and form
breeding pairs. Impregnated females drop eggs above thickets of water plants
like rain. Many eggs will be lost, but ones that will survive are quite enough
for reproduction of the species.
Life of adult insectfishes even without additional troubles is short, but many
of them perish from attacks of halcyon terns. When swarms of gracile insectfish
imagoes hover in an endless round dance, halcyon terns sweep through them, catching
two or even three insects at once. It happens even, that seized females continue
scattering their eggs until the bird swallows them. Lots of eggs of insectfishes
will be carried away by streams to the rivers, but the most part of them will
stall in aquatic moss. Minute nymphs burst from eggs; they eat various microscopic
low-life and hide among stalks of aquatic moss. With aging they begin spending
more time in swimming, and then they are gradually carried by the current to
the main channels of the rivers. Here in rather quiet places they form shoals,
feed and grow to return in once to upper courses of the rivers where their life
began, but using their own wings.
Through swarms of insectfish imagoes adult flattened stream dragonfly flies
by, sparkling its blue abdomen. A long time ago, the last year, it had been
a nymph and, maybe, hunted these particular insectfishes until they had swum
away to the river. But now it is safe for insectfish imagoes though their swarm
gives way respectfully to this shining bright insect. Adult flattened stream
dragonfly eats small insects – it “trawls” midges by legs covered with hairs
and put together like a basket.
Bright colouring of flattened stream dragonflies helps them to distinguish each
other at a great distance. In visible light male and female of this species
look absolutely equally. But insects distinguish ultra-violet light, and in
this light the basic distinctions between male and female become clearly seen.
Promptly flying above reeds, males of flattened dragonfly notice females at
which abdomens reflect ultra-violet light, forming cross-striped pattern. Having
noticed the female, males rush to it from all directions and begin hovering
near it, trying to perch on its abdomen for pairing. Courtship games of this
species represent the true race which looks very impressively because of flashes
of blue color in rays of Antarctic sun. After pairing female finds suitable
place for eggs: thickets of aquatic moss, which strands wave in water. The moss
forms a dense texture of stalks on which surface spore-bearing capsules stick
out. Having chosen suitable place, the insect puts its abdomen into the mat
and lays eggs. Nymphs will spend first period of life in moss, and then would
creep away to begin the life of solitary hunters.
In spite of the fact that Antarctica is still located at the pole, and in the
center of the continent the huge glacier is not thawing, summer at the edges
of the continent happens to be rather hot. Polar day began, and the sun at night
hours has only “struck" horizon with the bottom edge of disk though at
this time weather is little bit cooler. “Night” is not a time for insects: in
cool air their activity is reduced, and they simply have a rest. Flattened stream
dragonflies at this time hang motionlessly on stalks of reed and sedge. It is
too cold to them to fly now. When the sun begins its rise above horizon, and
its rays hit dragonflies hanging on leaves, insects turn backs to the sun. Their
thoraxes are colored black not without reason – such colouring allows to warm
up flight muscles faster, and the insect can take off. But someone has had time
to be warmed up much earlier …
From thickets the shining dark blue lightning surrounded with black aura darts
off and forces down in air one of flattened stream dragonflies. The creature
interrupted the life of this dragonfly is also a dragonfly, but of another species,
that is much larger and aggressive. Having finished in air with its prey, it
throws the rests in water, makes a turn in air and perches on tall inflorescence
of sedge. The feature of this insect – black, as if smoked translucent wings,
is evident at once. This insect is equitably named as “black emperor” – it is
the true tyrant of local insects, and at times not only of them.
Due to the black wings working as a heating element “black emperor” was warmed
up earlier, than flattened stream dragonflies, and has skilfully taken advantage
of it. This dragonfly species does not hunt any kind of small fry like mosquitoes
or midges – it is an expert in “big game” in scale of the world of insects.
From time to time “black emperors” rush through swarms of smaller Antarctic
dragonflies, catching them and devouring hurriedly. These ones represent some
kind of “micro-falcons” in ecosystem of Antarctic rivers.
“Black emperor” is an insect which at times challenges even to birds. It has
keen sense of smell, and sometimes these dragonflies involved with a smell of
blood gather on prey of falcon grackles. Their attacks are so resolute, that
the predatory bird, being hundreds times heavier, recedes and enables dragonflies
to use its prey.
Imagoes of voracious insectfish fly above the river. They flash their bright
colors, being as beautiful, as butterflies. This species is one of the brightest
insects of Antarctica, one of ornaments of riverbanks. Sparkling bright green
bodies, these dragonflies announce with their appearing: the warmest days of
summer have come. Only till two or three weeks they fly above the rivers, forming
pairs and laying hundreds of eggs. Their adult life is so short not only because
they love heat: the matter is that adult voracious insectfish eats of nothing
and lives only due to the stocks of nutrients accumulated at the nymph stage.
Therefore courtship flights at this species begin right after their wings stretch
and insects fly up for the first time. Males search for females and arrange
joint flights, sparkling green bands on their wings. Usually the swarm is quickly
separating to pairs, and for some time male flies, being coupled with female.
After pairing male quickly perishes, and female begins egg laying. For this
purpose it perches on plant stalk and puts its abdomen into the water. In leaf
axil of cane it lays a lump of slimy eggs containing about ten ones. After that
it flies up, moves to certain distance along the riverbank and repeats these
actions. Portions of eggs are scattered along the riverbank intentionally to
lower the competition between growing up nymphs of the same mother. One more
attractive place for egg laying is thicket of marsh plants floating on the surface
of certain backwater. Here the competition is less, and a place is more favourable:
right after hatching the nymph appears “at home”. But such place is very “expensive”
– females of voracious insectfishes do not tolerate competitors, and furiously
rush to the competitors decided to lay eggs beside. Attacking the competitor,
voracious insectfish female literally “rams” it by head, driving it away from
the chosen place. However, it is enough to wait a little, while dominant female
will fly out, and it is possible to lay eggs at the same place, but having fought
with other interested ones. Theoretically all dragonflies wishing it can lay
eggs in “prestigious” place… Or not all can. Some dragonflies perch on floating
plants at the safe distance from each other to lay eggs. They sparkle in sunlight
with their bodies, and they are noticed by hungry “black emperor”. Like a kite,
black-winged dragonfly rushes to insectfish imagoes. They fly away in all sides,
and the prompt chase begins. Wings of voracious insectfish imagoes sparkle in
sunlight, and one of them is followed by “black emperor”. It is stronger than
insectfish imago, which life resources are limited, and the result of chase
is in fact predetermined from the very beginning. It is not clear only, which
insectfish would be chosen as a prey by this one. Black-winged predator overtakes
its prey and seizes its abdomen. For some seconds both dragonflies somersault
in air, and then the bitten off head of insectfish imago falls to the grass,
and “black emperor” tears its body in flight.
“Black emperor” ends the food chain of the world of insects not only above,
but also under water. “Black emperor” nymph, the creature of frightening appearance,
corresponding in size to adult dragonfly, waits for prey, having dug in silt.
It creeps hardly, but nevertheless it can prey the fastest nymph of any insectfish
due to the way of movement inherited from ancestors. While in sight of “black
emperor” nymph there is no suitable prey, it tries not to give out its presence.
Only occasionally the rests of plants, under which it was dug at the bottom,
move slightly.
It is not necessary to wait for a long time for a proper moment for attack:
numerous shoal of stripe-tailed insectfish nymphs swims past, moving with black-and-white
gills growing on tips of their abdomens. When they swim up too close to hidden
“black emperor” nymph, the predator attacks them. Its abdomen is sharply contracted,
throwing out from rectum jet of water, and “black emperor” nymph, having pressed
its legs against the body, darts off from its shelter and runs into the shoal
of insectfishes. It misses a tiny bit only: palps close not on abdomen of insectfish
nymph, but on one of its gills which breaks away on the spot. Prey escapes,
being almost safe: certainly, after loss of one caudal gill it will swim slower
a little bit, but in general it is a norm of life for insectfishes. At the majority
of shoal members gills are injured, and at some there are even two their petals
torn off.
“Black emperor” nymph is dug in silt again, muddling it by “shots” of water
from its rectum. When at the bottom small pit is formed, nymph creeps into it
and freezes. Silt and rotten leaves, sedimenting on the bottom, mask the nymph
and it is ready to attack again.
From turbid water even more tempting prey appears – nymph of voracious insectfish.
The large striate creature swims at a great distance from hidden “black emperor”
nymph, but it looks very appetizing, and the predator attacks it from afar resolutely.
Nymph of voracious insectfish is a worthy opponent, and the most important act
of attack is to neutralize immediately its killing harpoon mask or to seize
this nymph in way preventing it to use its weapon. Having attacked from the
back, “black emperor” nymph grasps insectfish nymph from above, and literally
crushes prey’s thoracal segments by strong palps of its mask. It begins devouring
of voracious insectfish nymph even on having waited while its spasms will finish.
“Queen of hearts” nymphs swim in water thickness far from the coast: in this
way these phlegmatic creatures avoid attacks of “black emperor” nymphs. But
sooner or later they should make a step across edge of water and turn to adult
insects. For this important mission “queen of hearts” nymphs swim up to the
coast and get into the thickness of coastal vegetation to have metamorphosis
in secluded place. Having got out from water, they creep clumsily on legs poorly
adapted to it. Getting on plants, they creep on wide leaves and keep under them,
having hooked by claws against leaf edges. So they are less appreciable from
air at the most vulnerable moment of life. Metamorphosis at these dragonflies
is accompanied not only with reorganization of anatomy and physiology of an
animal. Even their biochemistry is modified at this time – in their bodies active
synthesis of poisonous substances begins. To the moment when wings of young
“queen of hearts” stretch and harden, the insect becomes completely inedible.
“Queens of hearts” fly up one by one from reeds, and join an endless round dance
of their congeners. These dragonflies are colored bright red-brown and look
very attractively. One-year-old halcyon tern, which had never seen such colouring
at dragonflies, rushes to the swarm of dragonflies and chases one of them. “Queens
of hearts” fly not so quickly, and in some seconds the bright dragonfly already
wriggles in tern’s beak. With prey in its beak the bird perches on stalk of
cane and begins to finish with an insect. With several impacts against the stalk
it stuns dragonfly and then tears off its wings. Having finished with it, tern
swallows the dragonfly, and… after few seconds begins coughing hoarsely, as
if has choked with something. A spasm of muscles of throat follows – and the
tormented body of dragonfly is belched with disgust and is fallen in water.
Chemical protection has worked, and the bird will remember for a long time that
bright color not always means good taste.
Having flied below, halcyon tern drinks water greedy for a long time. When burning
in its throat has abated a little, it has flied up above canes. Fast beside
it the swarm of bright “queens of hearts” hovers, but the bird even did not
want to look at them, though in nest its hungry chicks waited for its return,
and the tern itself was hungry.
According the time there is an early morning, but it is imperceptible in Antarctica
in summer: there is a polar day, and it is light and warm all day and night.
“Black emperor” nymph reached its maximum size gets out on reedmace stalk and
hides from undesirable witnesses. Its “crowning” begins: exuvia on its back
cracks, and nymph of frightening appearance undergoes metamorphosis, turning
to adult insect. Having left its exuvia becoming too close-fitting, young “black
emperor” does not make at all the majestic impression that is necessary to a
predator of such rank. But about one hour passes, and its wrinkled wings stretch
and harden. The insect moves them, as if tries its force, and prepares for the
very first flight in its life. Wings work with dry papery crash more and more,
and at last the insect comes off stalk and flies up. Having succeeded in underwater
hunt, “black emperor” tries itself in aerial hunting now. The first possible
prey it meets represents imagoes of stripe-tailed insectfishes – graceful, but
very fast creatures. The swarm of these thin damselflies colored black with
white cross strips hovers above small rivulet which coastal shallows are overgrown
with aquatic moss. The first approach of “black emperor” appears unsuccessful:
it had been noticed by one insectfish imago, and its rush aside thickets appeared
an alarm signal for other insects. The second attempt is also doomed for failure:
hunting is broken by halcyon tern. Having cut into insect swarm, it has grasped
two insectfish imagoes at once by long beak and has vanished. But “black emperor”
has one stealth in a stock: this insect hunts from an ambush. Having landed
on cane stalk imperceptibly, black-winged dragonfly waits while thin insectfish
imagoes will lose vigilance and will engage in their affairs again. Expectation
of the predator had been crowned with success: from the third attempt “black
emperor” rushes through the swarm of insectfish damselflies and succeeds to
catch a delicate insect. Having landed on cane umbel, the huge dragonfly eats
prey – the first for the adult air hunter.
“Black emperor” is the ruler of an empire of insects, but it is not an absolute
monarch in ecosystem of rivers of Antarctica. Here there are creatures which
it is afraid of fairly – these are halcyon terns. Quick birds are perfectly
equipped for catching of such large and dangerous insects, and swallow-lookers,
which catch tiny edible critters above meadows of Antarctica, are not their
equals. Halcyon tern with its powerful beak easily catches adult dragonflies
of any species and can finish freely with “black emperor”. “Black emperor” has
bad luck to be not protected from birds by poison like “queens of hearts” are,
and therefore it is compelled to hope only for its speed and acrobatic tricks.
Halcyon tern notices “black emperor” flying across the river. Bird has sharp
sight and not less sharp beak, and “black emperor” has much more pleasant taste
than “queens of hearts” flying fast beside. And tern rushes to chase for a large
dragonfly. Two darts of lightning – black and white – sweep above reeds, making
inconceivable loops in air. Sometimes black-winged dragonfly managed to escape
the bird, but once the bird’s beak has clicked not vainly.
Burdened with the caught dragonfly, halcyon tern returns to its nest. These
birds build rather friable nests of grass in reeds. In the nest two chicks are
waiting for this tern. Chicks of this species hatch from eggs already in down
and with opened eyes, but all the same they spend a lot of time in nest before
they will become fully fledged and will be ready to adult life. At these chicks
feathers on breast and wings have already started to appear, but there are also
the parts of body covered with the rests of down, because of what young terns
look tattered. They seem large-headed while have not become covered by feathers
completely yet. Waiting for parents, young birds perch on the edge of nest,
preening from time to time and driving away importunate mosquitoes and midges.
When one of parents brings food, chicks meet it noisily, wishing to receive
the whole portion individually. Having perched on the edge of nest, adult halcyon
tern presses dead body of “black emperor” by paw, tears it by beak in two, and
feeds chicks by turns. One of them has rather easily coped with its portion
– it has got soft abdomen of the insect. But the second one is compelled to
choke, swallowing wings which are almost equal in length to its height. But
it is helped very much by greed of its sibling: having noticed that near it
something large is eaten, it simply breaks off wings of dragonfly one by one
while convinced that they are absolutely inedible.
The whole riverbank is divided by halcyon terns into small nesting areas. If
the neighbour flies to another’s territory, nest owners drive it away, arranging
at times improvised fight in air. But such casual incident may repeat many times
at different sites of the river. At times the lawful owner of territory, expelling
a stranger, appears on its site itself, and roles are interchanged quite opposite.
Such incidents are absolutely safe, and at times involuntarily help birds to
remove the accumulated aggression. But they are not comparable with real threat
of local predatory birds. In Antarctica the main feathery predator of smaller
size is falcon grackle, the representative of passerine birds.
Falcon grackle, the magnificent male with bright yellow “glasses”, flies above
canes, looking for easy prey. It searches for nests of halcyon terns in which
there are chicks not able to fly yet. But it seems today feathery robber will
have no luck to diversify its menu with such prey – its appearing serves for
terns as powerful stimulus to uniting. Under the threat of the common danger
these birds as if forget insignificant territorial claims and unite to the flock.
The collectivism gives boldness to them, and fragile-looking birds attack predator.
They try to strike its head by wings and beaks, pull its tail and pull out feathers
from its back. Clicking its beak, falcon grackle tries to assume an offensive
posture, but halcyon terns are much quicker than it is, and predator succeeds
only to pull out a single feather from tail of one of them. In addition to infighting
terns apply weapon of “distant action”, rather safe to themselves, but very
effective against an aggressor: they fly above falcon grackle, bombarding it
with their sticky feces. The predator is powerless against such weapon, and
after several “volleys” it flies out disgracefully. And terns turn back to sole
owners of small nesting sites, and begin living with their trivial problems
again.
Having departed to safe distance from halcyon tern colony, falcon grackle begins
shaking off unpleasant “gifts” of these birds from its feathers. It literally
wallows in grass, and then runs to the river, and begins scratching and splashing
violently in shallow water.
It is necessary to search for the largest birds of Antarctica not at the meadows
of continent, but at sea coast. Their trumpet voices are audible hundreds of
meters far from the coast. These birds may not hide their presence – at the
continent there are no predators dangerous to them.
On sloping coast the noisy colony of large birds – thick-billed penguigulls
– spread. They differ from their relatives from subantarctic islands in the
impressive size (up to one meter high), more powerful constitution and deep
white beak looking like wide blade of knife. At adult birds edges of beak have
bright red color, and they drive young birds having unicolorous white beaks
as hard as they can. The colony lives its habitual life: birds move to the ocean
for food, and juveniles meet their parents with loud calls, demanding for food
at them. Sometimes hungry, but strong juveniles take food away at full coevals,
and then the fight begins at the coast. Parents do not separate juveniles, but
just drive each other away from the nesting territories. In other words, there
is a habitual vanity in their colony.
Scavengers can always find profit for themselves in the colony of these birds.
Usually the part of juveniles perishes from underfeeding or illnesses, and in
colony it is always possible to find some dead chicks. Falcon grackles visit
from time to time colonies of thick-billed penguigulls, but they not always
succeed to profit with carrion: adult birds are rather aggressive. They do not
have attachment to the lost relatives, as, for example, at elephants or apes.
They drive predators away only instinctively, seeing in them danger to posterity.
But other scavengers easily use a gratuitous entertainment. “Black emperors”
fly in the colony of penguigulls, being guided by smell of carrion. Having felt
the dead juvenile on which back some wounds from beaks of adult birds gape,
they move to its body. Dragonflies are fed on dead juvenile, flying up from
time to time when adult penguigulls hobble past. Adult penguigulls are too heavy
for hunting for dragonflies and can’t catch them or drive away from carrion.
But nevertheless dragonflies do not lose care, flying up when any penguigull
hobbles past, wagging clumsily.
From time to time from the ocean gloomy thunderclouds come and storm begins.
Waves pounce coast furiously, taking out from depth and casting ashore seaweed
and hundreds live creatures appeared helpless when faced to natural disaster.
Wind sweeps over the Antarctic meadows, and grasses wave under its inrush like
ocean waves. The wind gathers the tribute from Antarctic dragonflies, carrying
away tens of insects failed to hide to the sea, or throwing them to cold embraces
of the Central Antarctic Glacier, where helpless insects will simply freeze
in layer of ice. Once millions years ago, ancestors of Neocene Antarctic dragonflies
have got in this world with wind gusts. And now their descendants repeat the
destiny of their ancestors, being carried away to uncertainty. Most likely,
they will be simply lost in waves and will be eaten by fishes, but they would
be lucky enough, few of their number may colonize small island where there are
fresh water and food. But now dragonflies can do only one thing – cling harder
to grass by legs and mandibles and wait while storm will finish.
Nature can not behave violently eternally, and sooner or later clouds move away,
and the sky becomes clear again. Polar day goes on, and the sun quickly warms
up the ground. And insects return to life habitual for them. For “black emperors”
escaped during the storm there comes the time when it is necessary to work hard
to get food for them. Delicate thin insectfish imagoes which obviously can’t
resist to winds, most likely appear carried away to the sea, or freeze on the
surface of glacier, giving food to hundreds of thousands of microscopic cold-resistant
springtails. And other dragonflies are too strong and it is not so simply to
catch them. But nevertheless there is something attractive to “black emperors”
in storms. When the sun begins to warm again, from the coast the smell irresistibly
appetizing from the point of view of these dragonflies is spreading – the smell
of death and decay. Hundreds of fishes and other animals cast ashore began to
decay, and in air there is a biting stink mixed with pungent smells of rotten
seaweed. For the carrion-eating dragonflies it means the invitation to dinner,
and shortly after air will get warm enough at the coast hundreds of these black-winged
dragonflies already feast. Even falcon grackles flying after storm to the coast
glance cautiously at this swarm of wing-rustling creatures. If there is a lot
of meal, one or two birds, having taken courage, may steal fish or dead squid,
but more often they should wait while dragonflies will be saturated or to wander
knee-deep in water, gathering fish on which these dragonflies can’t land from
fear to wet their wings.
The giant shadow of nomad
albatross slides along the coast. This bird is one of the largest flying
creatures of Neocene. Its wingspan reaches five meters. Being the true lord
of heavens, it is rather clumsy on land because of long wings, therefore it
does not risk to land near to impressive thick-billed penguigulls.
When the huge shadow of this bird slides at the beach where dragonflies are
fed, insects are frightened and fly up. They may not to be afraid of this giant
bird – nomad albatross will hardly pay its regal attention to them. Its appearing
here is as if a reminder for feasting dragonflies: yes, they are kings of air,
but at this continent only.
Bestiary |
Stripe-tailed
insectfish (Tenuidryas fasciatocauda)
Order: Dragonflies (Odonata)
Family: Demoiselles (Calopterygidae)
Habitat: Antarctica, slowly flowing rivers.
Picture by Biolog
During the second half of Cenozoic era Antarctica was completely
covered with a layer of ice which reached the thickness of several kilometers.
The glacierization of continent had completely destroyed fauna of freshwater
fishes and other animals living in the rivers and lakes. When in Neocene this
continent began to free from an ice cover, at the plains and in mountains numerous
streams and rivers with cold and crystal-clear water had appeared. They remained
lifeless not for long: the wind brought from the nearest continents (Africa
and Australia) spores of algae which roughly developed in absence of competitors.
And when Antarctica had even more put in Indian Ocean, its reservoirs had been
settled by higher aquatic plants, whose seeds have got there with a wind or
on plumage of birds.
Among pioneer insects of Antarctica there were dragonflies. In a new inhabitancy,
lack enemies and competitors, they have roughly evolved and even managed to
occupy the ecological niches occupied by fishes at the other continents. And
day-flies and caddisflies, living at the adult stage not for long, have not
reached Antarctic Region: the oceans separating continent from other world are
too wide for it.
Graceful dragonflies rush above the Antarctic rivers in large swarms. They are
rather small (wingspan about 5 cm) and look very fragile. Body of such dragonfly
is very thin, black with white cross strips on abdomen; wings are absolutely
transparent with dense grid of costae. These dragonflies eat midges and other
tiny insects breeding plentifully in crystal-clear water of Antarctic rivers
originating in mountain glaciers. Life expectancy of each separate dragonfly
is insignificant: no more than 1-2 weeks. But they start to appear as soon as
air gets warm enough, and danger of night frosts will pass. And last of these
dragonflies may live almost until the Antarctic polar night.
The role of this species of dragonflies in ecosystem of Antarctic rivers is
very great: it is one of the basic inhabitants of the rivers. The adult insect,
however, does not play as great role in natural communities, as its nymph does.
Even the name of this insect – stripe-tailed insectfish – is determined not
by appearance of adult dragonfly, but by features of anatomy and way of life
of its nymph.
Nymphs of insectfish live in water, not betraying the “traditions” of ancestors
(however the dragonfly from Hawaiian Islands, which nymph lived on land, and
also nymphs of many fossil dragonflies found in land sediments had been known
to people). It keeps in thickness of water in schools like small fishes and
occupies their ecological niche in the rivers of Antarctic Region. The insect
swims actively, wriggling the whole body in horizontal plane that increases
its external similarity to fishes even more. Nymph’s body is extended and flexible,
its length is up to 3-3.5 cm, colored grayish-white.
Living in clean water, insectfish nymph is guided mainly with the help of sight.
Its eyes are well advanced, making about half of the size of head. To recognize
congeners, nymphs have the special marks well distinct from afar: external gills
on the tip of abdomen have contrast colouring – white with black tips.
Nymph also feels the presence of congeners with the help of sensory hairs covering
its body. Every nymph feels movements of congeners and tries to imitate them
in everything. Due to such behaviour the school of insectfish nymphs swims with
remarkable synchronism, looking like school of fishes. The larval stage at this
species proceeds up to 2 years, and in cold mountain lakes it may drag out twice
more.
Like nymphs of all other dragonflies, nymphs of stripe-tailed insectfish are
carnivorous. They eat tiny aquatic animals, catching them with the help of narrow
labial mask with two palps (labial mask is in fact a modified labium working
as a hand, characteristic for dragonfly nymphs). The basic food of these nymphs
includes tiny swimming worms and plankton crustaceans, and also its own smaller
relatives.
Adult damselflies of this species breed by disseminating their eggs above water.
One damselfly may lay up to 100 tiny eggs. They ripen in female’s oviducts for
a long time and after their appearing in water from them at once tiny nymphs
burst, which hide in thickets of aquatic moss. Having reached the size of 1.5-2
cm, they gather in schools and spend more and more time in thickness of water,
turning to pelagic animals.
“Queen
of hearts” damselfly (Titanagrion rubra)
Order: Dragonflies (Odonata)
Family: Narrow-winged damselflies (Coenagrionidae)
Habitat: Antarctica, slowly flowing rivers and lakes.
Picture by Alexey Tatarinov
Among dragonflies amazingly beautiful species may be seen frequently.
Some of them amaze with brightness and metal shine, others with refinement of
their shapes. Among dragonflies of Antarctica one large damselfly having wingspan
of up to 20 cm is especially remarkable in its beauty. It has got a name “queen
of hearts” quite reasonably – only few insects of such size and such bright
colouring may be found in the world. Imago of this species has transparent wings,
and the whole its body is red with brownish shade. The damselfly has the right
to have such bright colouring: it is supported with unpleasant taste and warns
predators that the insect is protected. “Queens of hearts” fly only in the hottest
weeks of Antarctic summer.
Nymph of this species takes very important place in ecosystem of Antarctic freshwater
bodies. It leads pelagic way of life and is very large (it reaches length of
10 cm and more). Legs of nymph are covered with hairs and are rather long (about
one third of the general length of an animal). Their basic function is to promote
hover of the nymph in water thickness. Usually they are simply spread wide in
sides. But in case of danger “queen of hearts” nymphs can swim quickly, moving
their legs like a larva of predatory water beetle.
Mask of “queen of hearts” nymph is wide; along the edge it is supplemented with
a plenty of hook-like bristles. Nymph eats small planktonic crustaceans, filtering
them with its labial mask. Thus the mask makes “raking” movements, at the same
time helping the nymph to swim forward. After every “rake” mandibles accurately
remove from mask crustaceans got stuck between bristles.
Voracious
insectfish (Macrocryodryas vorax)
Order: Dragonflies (Odonata)
Family: Demoiselles (Calopterygidae)
Habitat: Antarctica, rivers and lakes.
Picture by Biolog
At the Antarctic continent which had released in part from
an ice cover in Neocene, the same situation, as at the islands, but in scale
of the whole continent had repeated: actually uninhabited land had been occupied
by few animals able to fly, or by natives of the sea. Isolation of Antarctica
from other continents appeared reliable enough: not all possible migrants managed
to cross ocean even to reach this ground only. But those ones which had made
it faced the conditions far from being the best: the continent is located mostly
within Antarctic circle, and in winter here is the polar night, and the ground
is covered with thick layer of snow. But nevertheless the population of this
territory is rather diverse.
In Antarctica of Neocene epoch birds are found, and also there are numerous
insects.
Among insects in Antarctic Region dragonflies are especially widespread. These
winged predators occupy top levels of food pyramid in reservoirs, and in a biomass
they are comparable to migrating birds spending summer at this continent.
One reason of high variety of the Antarctic dragonflies is the absence of competitors
in fresh waters. Fishes of Antarctic Region are mainly marine ones spending
in fresh water only a part of their life and not rising in rivers far from sea.
And cold mountain streams and lakes having no connection to the ocean represent
an empire of insects. In water thousands of small damselfly nymphs slide, wriggling
their bodies. Here they substitute fishes. Microscopic worms, crustaceans and
other inhabitants of water turn to their food. At the bottom mosquito and fly
larvae swarm, on stones and the rests of plants midge larvae form true live
“carpets”. But, though here there are no fishes like a trout, in this world
there is a king of predators – it is a large (up to 10 cm long) gluttonous nymph
of voracious insectfish.
This species feeds on large insects, preying them one by one. Its basic hunting
device is its labial mask (the modified labium). Palps on mask form some kind
of “spear” piercing prey’s covers. Nymph stabs its prey, sharply darting mask
in it (the length of mask in straightened position makes up to half of length
of the whole body of nymph). Stab is put by palps nestled against each other
that penetrates through prey’s covers. Having pierced an armor of prey, palps
spread apart, having “anchored” inside and holding prey.
For predatory behavior and a mode of nymph movements this species of animals
has a specific epithet “voracious”. It is a relative of smaller species of insectfishes
and one of large species of damselflies of Neocene epoch.
After two years of “piracy” life nymph undergoes metamorphosis and turns to
adult insect. An adult damselfly is about 12 cm long, its wingspan is up to
15 cm. Wings are transparent; males have narrow cross stripe of green color
closer to the tips of wings. Abdomen of adult damselfly is colored metal green,
and abdomen tip is yellow, separated from the background coloration by black
cross strip.
Imago lives not for long – about one week only. Insects of this species emerge
in strictly limited period: in two warmest weeks of Antarctic summer. At this
time they continuously fly above lakes, searching for the partner for pairing.
The specific epithet “voracious” does not fit absolutely to adult damselfly
of this species. Imago has a digestive path and the mouthparts, but it eats
much less than adult damselflies of other species.
Imago only lays eggs, landing on floating plants. After that its organism promptly
grows old, and it perishes. Nymphs live among floating plants, avoiding in such
a way a competition to benthonic forms. For wintering nymphs leave floating
plants, hiding in thickets of coastal plants. Spring is the most difficult time
for them: floating plants have not grown up yet, and nymphs, having flocked
in thickets, begin to attack against each other. But when floating plants form
a mat on surface of water, the survived nymphs feel like in full safety: they
will not be found by gluttonous benthonic nymphs of other dragonflies, and the
casual bird will not peck them up from surface of water – leaves of plants cover
them from aerial predators.
Flattened
stream dragonfly (Cryolibella platyglossa)
Order: Dragonflies (Odonata)
Family: Skimmers (Libellulidae)
Habitat: Antarctica, fast-flowing streams and rivers.
Picture by Lambert
The rivers of Antarctica originate in glaciers and are remarkable
in crystal-clear and cold water. They hadn’t been settled by insects like day-flies
or caddisflies though at the other continents they prefer such habitats: it
is very difficult for these species to cross the seas separating Antarctica
from the world around. But other insects have easily made it, having filled
with life rivers of Antarctica.
Stones in channels of Antarctic streams are densely covered with “live moss”
– colonies of pearlworts and other sedentary animals. Here diverse midges which
have got to this continent with winds have found the new house. Midge larvae
settle on stones and plants plentifully. But here they have an enemy – the nymph
of one local dragonfly species, flattened stream dragonfly.
Dragonfly nymph of about 7 cm long with the wide flat body covered with rudiments
of wings slowly creeps on stones. It lives in streams with fast current, but
is not afraid to be washed away by water. Nymph is perfectly equipped to life
in the world of current water: on all its legs strong suckers are advanced.
To make a step, nymph lifts legs one by one and by turns stand them on new place.
In addition its body shape is those, that water itself presses this nymph to
the stone. Of course, this mode of movement is very slow, but prey of this nymph
is even slower: midge larvae spend almost the entire their life, being attached
to the same place.
Labial mask at this nymph is short, wide and flat, with cutting front edge.
Palps growing at the edges of mask are mobile and work as thumbs. When feeding,
nymph grasps sedentary midge larva with palps and simultaneously cuts it off
from substratum by edge of mask.
The development of nymph lasts for 2 years. Having reached the maximal length,
it creeps to the riverbank and sheds skin, turning to adult dragonfly. Adult
flattened stream dragonfly has transparent net-patterned wings and flattened
brightly colored shining abdomen seen from apart. At male abdomen is silvery
with bluish shine, reflecting a plenty of ultra-violet rays. At female abdomen
has metallic-blue color, but on each segment there is cross belt of hair, also
reflecting ultra-violet light. Therefore insects can distinguish representatives
of another gender from afar: they see the “ultra-violet” colouring hidden from
the naked eye.
But in the morning it is important to be warmed and to fly up in proper time,
and shining abdomen obviously does not promote it. But the head and thorax of
this insect are colored velvety black and quickly get warm in the morning. Adult
flattened stream dragonfly keeps an orientation of diet characteristic for its
nymph: it also eats midges, but adult ones in this case. Its legs are covered
from the inside with hairs forming true “plankton net” for smaller flying insects.
Darting through swarms of midges, this dragonfly catches some midges for one
rush and eats them in flight.
During the summer female lays eggs for some times. For this purpose it lands
on thickets of aquatic moss protruding from water, and puts its abdomen into
the tangle of stalks, pasting eggs to moss shoots. Soon nymphs hatch from eggs.
They eat the animals living in vegetation, and frequently larger nymphs eat
smaller ones. Having got stronger, nymphs leave moss and begin hunting midge
larvae in stream channels.
“Black
emperor” (Aeschnomima imperialis)
Order: Dragonflies (Odonata)
Family: Hawkers (Aeschnidae)
Habitat: Antarctica, slowly flowing rivers and lakes.
Picture by Alexey Tatarinov
In the world of insects there is as eager struggle for existence,
as among large animals. Here there are predators and prey also. A difference
is only in the number of participants of this struggle.
Because of its isolation from other continents Antarctica had been populated
only by few founder species. Not all settlers got accustomed to extreme conditions
of this continent, but those ones who managed to adapt, became the true owners
of the continent. Among the Antarctic insects there are species comparable in
ferocity and force to the most dangerous predators among vertebrates (of course,
adjusted for the size).
Throughout the summer above the wetlands of Antarctica swarms of mosquitoes
and midges hover. Small graceful damselflies dart through clouds of these insects,
hunting them. But these thin-bodies damselflies may fall prey to a predator.
They are hunted by birds, but it is rather easily to hide from chase of feathery
predator: damselflies are much faster and nimbler than they are, and besides
even from afar notice the birds flying by above endless thickets of graminoids
and sedges. And the most terrible enemies of insects are other insects. And
the top six-legged predator of Antarctica is furious “black emperor”.
“Black emperor” is a large dragonfly species, one of the largest insects of
Antarctica. Wingspan of this species is about 18 cm. The body has metallic dark
blue color with silvery cross strips. At male silvery strip on back third of
abdomen is very wide. Shine of these strips allows insects to distinguish congeners
during the prompt flight and to search for the breeding partner.
Black wings are of great importance in life of this insect: this adaptation
allows to be warmed quickly in rays of the morning sun. During the sunrise this
insect turns back to the sun, and its wings act as heat stores. Gradually the
whole dragonfly is warmed up, moves its wings actively and flies up. It’s possible
victims – dragonflies of other species – most likely still hang on grass leaves,
relying on their inconspicuousity. But frequently shine of wings gives out their
presence, and the predator gets breakfast almost for nothing.
At dragonflies not only adult insects, but also nymphs are predators. Nymph
of “black emperor” is an active aquatic predator partly replacing small predatory
fishes absent in rivers of Antarctica. Nymph is able not only to creep. It swims
quickly, bending its body in vertical plane. It eats larvae of other insects,
but prefers not to pursue them, but to attack from an ambush at the bottom.
Nymph traps its prey, being dug in silt or under the rests of plants. The length
of “black emperor” nymph may reach up to 10 cm – corresponding with an adult
insect. Its colouring varies from brown up to pale yellow depending on color
of bottom.
Its labial mask (lower lip) is very large, palpal lobes are saber-like and serrated
on internal edge. They seize prey strongly, not giving it of chances to escape.
“Black emperor” nymph attacks prey, using some kind of the “rocket engine”:
it sprays a powerful jet of water from rectum. Such way of movement is characteristic
for nymphs of large dragonflies in general. At this species it has considerably
amplified: due to elastic joints of segments its abdomen can stretch strongly,
taking a fair portion of water. Attacking its prey, nymph sharply contracts
muscles and literally “shoots” itself from the shelter to its prey.
“Childhood” at “black emperor” lasts for about three years – winters in Antarctica
are cold, and the period of active growth proceeds for some weeks only. Metamorphosis
takes place more often at the fourth year of life though some nymphs turn to
adult dragonflies already at the end of the third year of life. Thus, adults
of “black emperor” may be met throughout the duration of almost all polar summer.
“Black emperor” is an insect with the serious claim for a rank of “super-predator”
in the lightweight category. Sometimes this insect enters an antagonism even
with birds. The seized dragonfly of this species protects itself actively: it
bites, trying to get right to bird’s eye. Because of the bellicose behaviour
it feels like in safety even at the presence of large birds, and smaller ones
try to fly by this magnificent predator.
The interesting feature of this insect species is the adaptation of imago to
feeding on carrion: it is frequently possible to find adult insects on corpses
of sea birds or fishes cast ashore by storm. Sometimes adult dragonflies even
pursue the predatory birds which have caught prey: this dragonfly has good sense
of smell, and it sharply reacts to the smell of blood. Not being afraid of a
bird, the dragonfly can land on its prey and be fed. If the bird will try to
drive away the importunate messmate, the dragonfly attacks it itself, aiming
to bird’s eyes. It can even frighten the bird off and take advantage of results
of its hunt.
Halcyon
tern (Alcyosterna acutiptera)
Order: Charadriiforms (Charadriiformes)
Family: Dwarf, or Halcyon terns (Alcyosternidae)
Habitat: rivers and lakes of Antarctica, wintering in South America.
Picture by Pavel Volkov
In Cenozoic Antarctica was separated from other world by wide sea passages.
And the native fauna of this continent had been destroyed by glaciers. In Neocene,
when the glacier began to release edges of the continent gradually, at inhabitants
of other continents the opportunity to occupy free from ice areas of Antarctica
had appeared. Among them there were only those creatures that could fly. And
even among them only few managed to cross the sea and to reach Antarctica. But
at these lucky beggars the opportunity to evolve actively, occupying new and
atypical habitats had appeared. It had taken place so, for example, at terns
(Sterna): these sea birds have developed a source of food new to them – the
insects inhabiting Antarctica plentifully. Large birds became smaller and turned
similar to swallows both externally and in habit of life. So in Antarctica the
new species of birds had appeared – halcyon tern.
This species is a small bird: in size it exceeds sparrow slightly though it
seems larger because of long tail. Wings at this tern are pointed, and tail
is forked. But instead of short bill characteristic for swallows or swifts this
bird is equipped with the strong pointed beak making more than half of total
length of its head. Legs of halcyon tern had partly lost ancestral features:
the palama does not reach even the half of toe length, but on toes pointed claws
had developed. Halcyon tern is able to swarm up stalks of cane dexterously,
and it is capable to perch on wavering plant stalk precisely at full speed.
The plumage of these birds gives out their relationship with sea birds: it is
white, and only on head there is a black “cap”. Beak is yellow, and in mouth
cut it is red. Legs are also red.
This bird eats small live creatures, catching them in water or in air. The basic
prey of this bird includes dragonflies. They are eaten by halcyon tern at any
stage of life cycle. It catches adult dragonflies, easily chasing them in flight,
or gathering in the morning time from grass, while insects are not warmed up
yet to fly up. In addition it dexterously snatches swimming nymphs of damselflies
out from water. Probably, because of it this bird did not become an exact copy
of a swallow, but combines in its appearance features of swallows and halcyons.
Halcyon tern is a migrating bird. It spends winter in South America though sometimes
separate individuals, being obviously blown by winds, fly for wintering to Africa
or to Madagascar. During the migrations this bird safely lands on water and
can catch plankton organisms from sea surface. This bird flies to Antarctica
in the middle of spring and flies out in the beginning of an autumn, when the
number of dragonflies (their basic food) decreases.
As against other relatives, this bird does not form numerous congestions, nesting
at the riverbanks at the distance of several meters between their nests. However,
features of collective behaviour have still remained at them: birds drive predator
away together, operating bravely and consistently.
Nesting takes place once a season and is dated to the beginning of warm summer
days. Terns have no outstanding building talents and at times their building
skill is limited only to the choice by the bird of a place where it will lay
eggs, and this place simple becomes its native house without any preparations.
Other species of terns build friable nests of vegetation on trees or on the
ground. Perhaps, halcyon tern has reached the top of building skills, having
surpassed in it of all its relatives. It nests in canes similarly to small songbirds
of Holocene epoch, and builds nest in reeds by itself. The basis of its nest
is made of some cane stalks meshed to each other, the part from which is broken.
On such unsteady basis it makes nest looking like friable basket with low walls.
In clutch there may be up to 5 eggs. Female hatches chicks mainly. Chicks hatch
with opened eyes and covered with grey down with black longitudinal strips.
Chicks dried after hatching at once seize nest by claws; they would not drop
out of it even at high wind.
Development of chicks takes about five weeks. Young birds find the way to wintering
areas independently. Sexual maturity comes at them at one-year-old age, and
life expectancy makes about 8 years.
This species of birds is discovered by Simon, the forum member.
Thick-billed
penguigull (Sphenicilarus crassirostris)
Order: Charadriifoorms (Charadriiformes)
Family: Penguigulls (Sphenicilariidae)
Habitat: sea coast of Antarctica.
The majority of species of inhabitants of Antarctica avoids meetings with winter.
Small animals like insects simply go into hibernation, having hidden in secluded
places under vegetative dust. Other ones like the majority of birds simply fly
out to the north, to warmer areas. Some of them hasten to South America, others
winter in Africa. But some birds keep activity the year round, not leaving the
native land. Those, for example, are small mousebirds digging holes in thickness
of snow during the whole winter. But there are also larger inhabitants in Antarctica.
They may be found out at the coast of ocean – trumpet voices of these birds
are audible from far.
After the ecological accidents which had taken place at the boundary of Holocene
and Neocene, the number of sea birds like penguins had greatly decreased, and
they had died out soon. But to change them the strange birds evolved, being
also not able to fly. They were descendants of gulls, flightless penguigulls,
birds with flipper-like wings, searching for food in the ocean. At Subantarctic
islands rather small common penguigull (Sphenicilarus apterus) lives, but in
continental Antarctic its larger relative – thick-billed penguigull – lives.
Like its smaller relative it forms the colonies numbering up to two or three
hundreds of birds.
Thick-billed penguigull is sea-dwelling flightless bird similar in constitution
to penguins and auks. Growth of this bird reaches almost one meter. Legs are
shifted back, therefore during the movement on the ground bird keeps its body
in vertical position. But in water it feels like as freely, as a fish, propelling
itself with wide paws equipped with palamae. During the swiming bird also uses
the reduced wings covered with very dense feathers. It swims in a manner of
penguins and sea lions, making by wings the same movements, as at flight. It
is able to dive deep (up to 60 meters), eats schooling fish and invertebrates
– krill and small squids.
The body is colored bluish-grey from above; head and stomach are white. Beak
is very deep, of yellowish-white color. On edge of lower jaw bright red strip
stretches – it is a signal for chicks during their feeding. Giving food to chicks,
the parent regurgitates the caught animals so that they appear as close as possible
to this strip, and the chick instinctively pecks this strip to find food.
Thick-billed penguigull spends the year round at the coast of Antarctica, preferring
stony beaches. When at the end of spring the ocean will get warmer and numerous
small animals appear there, the courtship season begins. Pairs are formed only
for one summer. Courtship displays are accompanied by loud calls and sometimes
males even combat, seizing each other by powerful beaks against wing or nape.
Courting for the female, male feeds her with fish. The pair of birds arranges
the nest (they dig simple pit among stones) and female lays two or three motley
eggs. Mainly female is engaged in incubation, and male is busy in food getting
for the most part of time. Chicks hatch covered with brown down with small black
spots. They have opened eyes and are mobile, are able to walk, but prefer to
remain in nest for the sake of their own safety. From all sides each chick is
surrounded by neighbours which strive to peck another’s posterity every time.
Young birds differ from adults in one-colour beak lack of red strip. It will
appear at the third year of life, and it will mean that the bird became adult
and is ready to get its own posterity.
In winter birds of this species frequently appear on ice. Sometimes ice floes,
breaking away from the main ice mass, carry away birds to more northern latitudes.
But thick-billed penguigulls always can return home after such incident: they
are able to swim for some days in succession, having an occasional rest on small
ice floes or on other floating objects.
Next |