Of Arachnids and Insects

Posted: March 7, 2010 in Nature
Tags: , , , ,

I’ve been watching insects and arachnids for nearly all my life.  In the Philippines, there is such a large variety of insects, even in one’s own backyard. I remember catching dragonflies by the tips of their slender wings, picking up beetles and Goliaths, and netting butterflies for science classes – all just to set them free a day later. This is a far cry from the bugphobic culture in the West. While I don’t go out of my way to catch bugs, I still get to appreciate them in whatever shape or form they are crawling or flying in (as long as they are outside the house, where they belong).

Lately, I have been pondering the evolution of insects and arachnids. While I am a demi-scientist (that is, one in nature, if not by designation since I have yet to earn a master’s), I specialize in physics and inanimate objects, not living creatures. So I am neither a biologist or entomologist. However, I am curious all the same, and will pose these questions for posterity.

Here’s what has been bugging me lately (no pun intended): Was it a fluke that, on the scales of Nature, the bug-sized predators are predominantly arachnids, and everything else is an insect? It’s often been taken for granted that both insects (subphylum Hexapoda) and arachnids (subphylum chelicerata, class Arachnada) both have the same phylum as Arthropods, according to the rigid taxonomic structure of animal classification. The similarities supposedly end there, and any other mention of comparisons are barely made in textbooks or scientific journals.

Yet, the lives of spiders, ticks, and most of the smaller four-legged creatures, are so closely intertwined with that of their twice-removed and distant four-legged relatives, that it pleads for a story to explain why they are such.  The first obvious difference, of course, is the number of legs: Insects have six, arachnids have eight. But if we consider the wings as an extra pair of appendages, then insects are on par with arachnids.

I have yet to learn about the success ratio of a spider on the hunt. However, I was fortunate enough to observe a few spiders in my old apartment. Depending on their location and proximity to sources of insects, a spider could be lucky and nab a meal, one out of six or even five times. However, being able to fly would be a serious game-changer for a hungry critter.

The wings are a propelling mechanism that allow an insect to cover large distances in a split second, in any direction. Arachnids, on the other hand, use the hind legs of their four pairs as a spring to propel them, but usually only in one direction. For any creature, freedom of movement and latitude may be just as important, if not more so, than range of motion, especially when it comes to fighting or fleeing.

Here is my semi-mythological arc. When some of the arthropods mutated away from the compound-eyes of insects, to the simple and multiple eye structure of arachnids, they saw how their brethren looked like… and some of them looked good enough to eat! Lo and behold, a breed of carnivores was born, that loved the flesh of bugs. Mother Nature was upset at how the new creatures, who called themselves spiders, took unfair advantage of the situation. If they kept chowing down on their winged relatives, there would hardly be any insects left.

So, to even the score, Mother Nature said, “Very well, you can have your insects and eat them, too.  BUT… you will give up your wings.  In return and just to sweeten the deal, you get an extra pair of legs.” The spiders snickered and said, “Fair enough. We hardly use those things anyway…”  POOF! Gone were the wings, and then the spiders realized, “This was harder than we thought.” And that’s how insects kept their wings, but the spiders were out of luck. Thank goodness, too. Spiders are best appreciated from a distance – and as long as they’re not flying.

Copyright Anabasius 2010


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