Wilderness Underfoot: First flying animals

StoryImage( ‘/Images/Story//Auto-img-114850059122120.jpg’, ”, ‘Early flying insects of the coal forest –About the size of a hornet, Eubleptus (on the leaf) is one of the smaller insects of the Carboniferous Period, 300 million years ago. Giant dragonflies of that time (inset picture), with wingspans reaching 3 feet across, were capable of preying on small reptiles and amphibians.’);
StoryImage( ‘/Images/Story//Auto-img-114850060322120.jpg’, ”, ‘Largest modern flying insect – The atlas moth of Southeast Asia has a 1-foot wingspan.’);
StoryImage( ‘/Images/Story//Auto-img-114850080322120.jpg’, ”, ‘Smallest modern flying insect – Dicopomorpha echmepterygis, a parasitic wasp, is just more than a tenth of a millimeter long!’);

By the time bony creatures took to the land on legs, slogging around in ancient swamps, the insects had already mastered flight.

Insects have ruled the skies for 360 million years—long before the pterosaurs, the birds and the bats. With a wing up on all the other flyers, insects have dominated the air in skill, diversity and sheer numbers. Amazingly, they’re the only flying animals that didn’t have to give up a pair of walking limbs to gain wings.

Just where insects’ wings came from is a matter of much debate. It was Jarmila Kukalova-Peck, the foremost expert on fossil insects, who first proposed a now widely accepted view that wings evolved from branches extending from legs. Over time, these branches developed into small flaps that allowed insects to jump a little farther or to quickly skim across the surface of ponds like modern stoneflies. As the flaps evolved, insects gained speed and maneuverability.

Today, flying insects use an assortment of flapping and gliding techniques, with added tricks that help in their effort to defy gravity. The wings beat slower in larger insects, such as butterflies and moths (at four to 20 beats per second), and faster in smaller insects such as flies and mosquitoes (at more than 1,000 beats per second). Because the wing muscles don’t actually have a fast enough “firing rate” to beat so rapidly, small insects rely on tiny springs within the muscles to bounce the carapace itself, causing it to vibrate at higher and higher frequencies with only intermittent nerve firings. Flies have further adapted by converting their hind wings into gyroscopes, allowing these pests to annoy us with uncanny deftness!

Flight gave insects an enormous early advantage over other animals. Initially, the air was merely a safe place to retreat from land-bound predators, but it also gave insects more opportunities to find food and new habitats. These same advantages ultimately helped other flying animals as well, but because of insects’ fast lifespan and tendency to produce lots of offspring, they maintained evolutionary dominance. Arguably, the only creatures that are better at the evolution game are microbes, and even microbes can’t match insect diversity. At least a million insect species have been identified, and some entomologists estimate that as many as 30 million species may exist.

From the May 24-30, 2006, issue

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