Wingless Insects

Flight among insects are varied. Some fly, some do not and some have forgotten it. There are numerous different groups of insects who have lost their wings or greatly reduced them. Unlike primitively wingless insects such as silverfish, fleas and lice have lost the wings their ancestors once had.

From left to right: silverfish, flea and lice

Female gypsy moths have underdeveloped wing muscles and don't fly. They don't need to, for the males fly to them, attracted by a chemical lure which they can detect at astounding dilutions. If the females were to move as well as the males, the system probably wouldn't work, for by the time the male had flown up the slowly drifting chemical gradient, its source would have moved on.

The female of the dreaded gypsy moth

Unlike most insects, which have four wings, the flies, as their latin name Diptera suggests, have only two. The second pair of wings has become reduced to halteres.

Diptera

The second pair of wings have become reduced to a pair of halteres. These swing about like very high speed Indian clubs, which they resemble, functioning as tiny gyroscopes. We know these halteres are vestigial remains of wings for several reasons
- they occupy exactly the same place in the third segment of the thorax as the flying wing occupies in the second thoracic segment (and the third too in other insects).
- they move in a figure of eight pattern as the wings of flies.
- they have the same embryology as wings and, although they are tiny, if you look at them carefully, especially during development, you can see that they are stunted wings, clearly modified.
- all insect wings have tiny sense organs in the base, which detect twisting and other forces. The sense organs at the base of halteres are very similar.

Halteres on a cranefly

Halteres are what makes between stable and unstable fliers. In any flying machine, there is a trade-off between stability and maneuverability. John Maynard Smith pointed out that animals lose inherent stability in the interests of increased maneuverability, but paying for it in the form of increased instrumentation and computation capability - brain power. The four winged ancestors of flies probably had long abdomens which would make them stable. All four wings would have acted as rudimentary gyroscopes. The ancestors of flies started to move along the stability continuum becoming more maneuverable and less stable as the abdomen got shorter. The hind wings started to shift more towards the gyroscopic function (which they had always performed, in a small way, as wings), becoming smaller, and heavier for their size, while the forewings enlarged to take over more of the flying. There would have been a gradual continuum of change, as the forewings assumed ever more of the burden of aviation, while the hind wings shrank to take over the avionics.

Worker ants have lost their wings, but not the capacity to grow wings. They lost their wings in evolution because they are a nuisance and get in the way underground. Queen ants and male ants have wings and worker ants are females who could have become queens but for environmental reasons (not genetic) failed to become queens. Queen ants use their wings only once, to fly out of the natal nest, find a mate and then settle down to dig a hole for a new nest. As they begin their new life underground the first thing they do is lose their wings, in some cases by literally biting them off.

An additional reason for winglessness is an evolutionary defense mechanism of assuming a protective resemblance to ants, either (or both) to fool the ants or to fool would-be predators who might otherwise pick them out from among the less palatable and better protected ants.

Wingless Birds

Not all birds fly. Ostriches and Emus are fast runners that never fly. But all birds carry at least relics of the apparatus of flight.

Ostrich Wing Stubs are only used for balancing and steering while running and when they enter into social and sexual displays.

Kiwi wings are too small to be seen outside the birds fine coat of feathers, but vestiges of wing bones are there.

Moas (which got extinct 1500AD)

Moas have lost their wings entirely. Their home country of New Zealand has more than its fair share of flightless birds, probably because the absence of mammals left wide open niches to be filled by any creature that could get there by flying. But those flying pioneers, having arrived on wings, later lost them as they filled the vacant mammal roles on the ground. This probably doesnt apply to the moas themselves, whose ancestors, as it happened, were already flightless before the great southern continent of Gondwana broke up into fragments, New Zealand among them, each bearing its own cargo of Gondwanan animals. But it sure does apply to kakapos, New Zealand's flightless parrots, whose flying ancestors lived so recently that kakapos still try to fly although they lack the equipment to succeed.

Kakapos, the heavyweight champion of all parrots

Penguins and Galapagos Cormorants are another two birds who use their wings for other purposes than flight. Ostriches, emus and rheas are great runners, but penguins and Galapagos flightless cormorants are great swimmers. But unlike penguins, who use their short wings to fly underwater, Galapagos cormorants propel themselves with their powerful legs and huge webbed feet, using their wings only as stablizers.

Galapagos Cormorants

But all flightless birds, including ostriches and their kind, which lost their wings a very long time ago, are clearly descended from ancestors that used them to fly.

Whales

Whales and Dolphins (which are actually smaller whales) evolved from land creatures. You don't have to dig very deep inside a dolphin to uncover its history of life on dry land. Despite its streamlined, fish-like exterior, and despite the fact that it now makes its entire living in the sea and would soon die if beached, a dolphin has land mammal written all over it.

blowhole of a dolphin

Firstly, it has lungs not gills, and will drown like any land animal if prevented from coming up for air, although it can hold its breath for much longer than a land mammal. Instead of breathing through two little nostrils at the end of its nose, it has a single nostril in the top of its head, which enables it to breathe while only just breaking the surface (see blowhole in the picture). This blowhole has a tight sealing valve to keep water out, and a wide bore to minimize the time needed for breathing.

The dolphins blowhole goes to great lengths to correct a problem that would never have arisen at all if only it breathed with gills, like a fish. And many of the details of the blowhole can be seen as corrections to secondary problems that arose when the air intake migrated from the nostrils to the top of the head.

Another indication of its land origins is that although whales have no hind legs, there are tiny bones, buried deep inside them, which are the remnants of the pelvic girdle and hind legs of their long-gone walking ancestors. The same is true of the sirenians or sea cows.

The skeleton of a whale. Notice (c) the hind legs that have no utility otherwise

Sirenians are very different from whales and dolphins but they are the only other group of wholly marine mammals that never come ashore. Where dolphins are fast, actively intelligent carnivores, manatees and dungogs are slow, dreamy herbivores. Manatees and Dungongs achieve hydrostatic equilibrium without the swim bladder that fishes have but with the use of heavy bones as a counterweight to the natural buyoancy of their blubber. Their specific gravity is therefore very close to that of water and they can make fine adjustments to it by pulling in or expanding the rib cage. The precision of their buoyancy control is enhanced by the possession of a seperate cavity for each lung: they have two independant diaphragms.

Dolphins and whales, dungongs and manatees give birth to live babies, like all mammals. That habit is not actually peculiar to mammals. Many fish are livebearers, but they do in a very different way. The dolpins placenta is unmistakably mammalian, and so is its habit of suckling the young with milk. Its brain, is also beyond question the brain of a mammal, and a very advanced mammal at that. The cerebral cortex of a mammal is a sheet of grey matter, wrapped around the outside of the brain. Getting brainier partly consists in increasing the area of the sheet. This could be done by increasing the total size of the brain, and of the skull that houses it. But there are downsides to having a big skull. It makes it harder to be born, for one thing. As a result, brainy mammals contrive to increase the area of the sheet while staying within limits set by the skull, and they do it by throwing the whole sheet into deep folds and fissures. This is why the human brain looks like a wrinkled walnut; and the brains of dolpins and whales are the only ones to rival those of us apes for wrinkliness.

whale brain

human brain

fish brain

Fish brains don't have wrinkles at all. Indeed, they don't have a cerebral cortex, and the whole brain is tiny compared to a dolpins or humans. This is another of dolphins mammalian history, along with the placenta, milk, a four-chambered heart, a lower jaw having only a single bone, warm-bloodedness and many other specifically mammalian features.

Fish

When we say fish, we generally imply anything that lives in water. But the dictionary defines fish as - any of various cold-blooded aquatic vertebrates having gills, commonly fins and typically an elongated body covered with scales. Now this definition excludes a lot of sea animals.

Dungongs

whales

Whales and dungongs come from a lineage of land animals. So there were some creatures that emerged from the sea to land, which was a major evolutionary step, and some who went back to the sea after their shortlived land habitation. Seals and Sea lions have only gone part-way back. But whales (including the small whales we call dolphins) and dungongs with their close cousins the manatees, ceased to be land creatures altogether and reverted to the full marine habits of their remote ancestors. But they do, however, still breathe air, having never developed anything equivalent to the gills of their earlier marine progenitors. Other animals that have returned from land to water, at least some of the time, are pond snails, water spiders, water beetles, crocodiles, otters, sea snakes, water shrews, Galapagos flightless cormorants, Galapagos marine iguanas, yapoks, platypuses, penguins and turtles.

Instead of spinning regular silk webs, they form platicy, silky air bubbles on the surface of water