Insects emerged 480 million years ago and developed flight 400 million years ago. With 90% of life forms on Earth being insects, they must have gone through numerous adjustments and transformations so far.
Another class of animals that have developed flight are the birds. Flightless birds are not out of the common, especially among island birds. When birds relocate to an island, it may be turn out beneficial to redirect the energy necessary for flight toward other functions or to avoid being blow away during storms.
Insects, however, do not seem to have lost their ability to fly once they have acquired it.
Are there flightless insects stemming from insects that have lost their ability to fly? And if not, why?
There is a great diversity among insects, which suggests a dynamic adaptability.
But they don’t seem to lose flight, do they?
There are many flightless insects on islands, for the same reasons that birds become flightless on islands. First, although flight was necessary to reach the island in the first place, once there individuals that fly risk being blown out to sea and dying. Second is the energy saving resulting from not having to develop and maintain wings and wing muscles. In the case of birds, one of the factors is the absence of mammalian predators on oceanic islands. This is less important for insects, since there will be birds and predatory insects there.
I found the arizona.edu page interesting because it emphasizes the importance of a stable, secure environment for insect species to experience flight loss. If insects do not need to travel far, they will not need to fly. On the other hand, island birds do not need to travel far either - so the stable, secure environment may play a role in a bird’s flight loss as well. But when you compare the two classes of animals, they seem so unlike each other. The advantages of flight appear to spell differently for insects and birds as life cycles in birds and insects are so different after all…
It may be as simple as the differing scale. Any given insect individual can thrive in a territory maybe 30 feet on a side. Any given bird individual may need more like 1/4 square mile ~= 1200 feet on a side.
Islands big enough to seem as spacious as a continent to a cohort of insects will seem very confining to a cohort of birds.
The only large flightless land birds are the ratites, the Ostrich, rheas, emus, cassowaries, and kiwis. The ones that live in continental areas with mammalian predators are large, swift, and feisty enough to protect themselves. Interestingly, each of the major branches seems to be descended separately from flying ancestors, and acquired flightlessness independently.
Although bats have reached many isolated islands, none have become flightless, perhaps because unlike birds their hind legs are too modified for them to easily become bipedal. However, the New Zealand Short-tailed Bat is semi-terrestrial, scrambling about on the forest floor to hunt insects.
Certain insects are primitively flightless, never having evolved wings. These include silverfish and some less well known groups. There are also some groups previously classified as insects like springtails that are primitively flightless.