Science For Everyone - Spiders, Insects, and Wings

Copyright © Karl Dahlke, 2022

Have you thought about spiders lately? 🕷 45 thousand species, and none of them have wings. In contrast, wings are central to the insect world. Some insects, like fleas, have lost their wings through evolution, because wings are disadvantageous, as they crawl through and live in dense fur - but their ancestors, mecoptera, possess wings.

Spiders and insects are similar in many ways, and live in so many of the same environments, you would think some spider would have developed wings, yet no wings for the arachnids. This suggests wing development is not a trivial matter - a miracle that evolution stumbled upon once, at the top of the insect line.

Let's step back and look. Spiders and insects have a common body plan: head, thorax, abdomen. The spider thorax has two segments, each segment with two pair of legs, thus 8 legs. The insect thorax has three segments, each with a pair of legs, thus 6 legs. Of course there are centipedes and millipedes with many segments and many legs, but that's another story.

Most insects have wings on the back two segments, thus 4 wings. Why the back two? Perhaps because the abdomen is larger and heavier than the head. So important are the wings, that insect orders are often named for the structure of wings. ptera is latin for wing, and we have: lepidoptera (butterflies and moths), phthiraptera (biting lice), siphonaptera (fleas), hemiptera (true bugs), dermaptera (earwigs), orthoptera (grasshoppers, crickets, and locusts), ephemeroptera (mayflies), hymenoptera (bees, ants, and wasps), diptera (flies and mosquitoes), coleoptera (beetles), plecoptera (stoneflies), and many other orders.

di is latin for two, and thus, diptera have only two wings, on the middle segment. The back wings are replaced with halters, sensing organs that help with flight. Thus flies, and unfortunately mosquitoes, can do amazing acrobatics that would make a hummingbird jealous. Think about the way they can hover, dart about, and change direction at a moment's notice. You'll have a harder time swatting a fly than a bee.

Despite its name, a firefly is not a fly, but rather, a beetle, with four wings. There are about 2,000 species of fireflies, contributing to the 400,000 species of beetles, that constitute nearly a quarter of all animal species on Earth. biologists often remark that if a Creator fashioned each animal "after his kind", as suggested by Genesis 1:24, then he has an inordinate fondness for beetles.

A firefly generates flashes of light through a process called bioluminescence, primarily to attract a mate. Why then doesn't the firefly get eaten? Whenever an animal advertises itself, through bright colors or flashing lights or other signals, it is often poisonous or harmful in some fashion. The signal doesn't mean, “Hey, come over here and eat me”, that wouldn't make evolutionary sense. It usually means, “Stay away from me, I'm dangerous, or at least not worth your time.” This is illustrated by the stripes on a skunk, or the bright colors on the poison dart frogs of Central and South America. As it turns out, many species of firefly contain steroid poisons similar to these frogs. They can flash away without being eaten, because they taste bad, and if enough fireflies are ingested, the predator could become ill.

Even larvae can emit light, and these are sometimes called glowworms. In 1902, Paul Lincke wrote an operetta, Lysistrata, that contained the song Glow-Worm. Johnny Mercer modified the lyrics for a 1952 recording by the Mills Brothers, which spent 21 weeks on the charts, including 3 weeks at number 1.

Hemi is Greek for half, as in hemisphere, thus hemiptera are the half-wing bugs, including cicadas, aphids, and leafhoppers. The name refers to the insect's forewings, which are hardened near the base, and thin and membranous near the ends. This gives them the appearance of being a half wing.

Lepidoptera means scaled wings, as many butterflies have tiny scales on their wings. These scales produce the beautiful colors that collectors admire.

Fleas have no wings, so what's up with their name? In Greek, the prefix a means not. We see this in a few English words: amoral, asexual, atypical, apolitical. Thus siphonaptera means a tube like mouth part for sucking blood, and no wings.

The other orders also have names consistent with their morphology, if you happen to speak Greek.

Meantime, none of the spiders, or scorpions or other arachnids, have wings. Some can spin a web of thin silk and put it up like a sail and ride the wind, but (in your best Tom Hanks voice), “that's not flying, that's falling with style.”

Speaking of spiders, if you're a Star Trek fan, then you want to get Kingdom of the Spiders, starring William Shatner. He does his overacting thing, but you'd be disappointed if he didn't. It's a decent movie, and fun to watch, especially if you're afraid of spiders. At least they don't have wings, so they can't fly up and swarm around your face.

There is a great deal of information about insect wings here.