A super-sized bug

I’m not a big fan of insects. They have entirely too many legs for me to be comfortable with. Granted, there are exceptions. I like butterflies, big fuzzy bumblebees, dragonflies and grasshoppers. I don’t even mind certain kinds of ants (though not if they’re in my home). Oh, and of course I like the Katydid. But there are some bugs that I just cannot stand. Spiders, earwigs, centipedes, beetles, flies, mosquitoes, wasps, silverfish, termites, cockroaches, mites, ticks, weevils, scorpions, fleas… you get the idea. They make my skin crawl. Of course, I know it’s somewhat irrational. Even though some insects are poisonous, most have more reason to be scared of me than I do of them. And I’m easily many orders of magnitude larger than them – so it’s easy enough for me to squish them.

It’s this size difference that I want to talk about today – specifically in light of an article that I found which made me realize that bugs were not always the size they are today.

Paleontologists from the University of Bristol have recently discovered a fossil of the world’s largest bug – at a whopping 2.5 meters long. That’s 8 feet. That’s over 2 feet longer than I am tall! Whoa.
(To see a diagram comparing this insect to a human, you can see one at: http://www.msnbc.msn.com/id/21906979/)

The bug in question is an Eurypterid, or ancient sea scorpion. Eurypterids are believed to be aquatic ancestors of modern-day arachnids (which includes scorpions, spiders, and horseshoe crabs). They were predators of the ancient seas, from the Cambrian to the Permian periods (500 to 250 million years ago). Eurypterids had segmented bodies, a long, tapering, flexible tail, and claws protruding from their heads. They were ubiquitous in their day, and their fossils have been discovered all around the world. Most of the fossils are of small specimens – 1 to 15 inches long. However, the fossil announced this year was 18 inches long – and that was just one of its claws!

The finding was just published in the November edition of the Royal Society's Biology letters. However, the fossil itself was discovered several years ago in Germany by paleobiologist Dr. Markus Poschmann. Since then, Dr. Poschmann has worked with Dr. Simon Braddy to determine how big an animal would have to be to have a claw of that size. It turns out that sea scorpions have a constant ratio between claw size and body length. With that ratio, they calculated that a sea scorpion with an 18 inch claw would have a body 8 feet long – 11 feet if you include the reach of the claws.

Exactly how and why this creature grew so large is unknown. Scientists have long known that giant land-based bugs existed during the Carboniferous period, around 300 million years ago. At that time, there was a boost in atmospheric oxygen, which might have allowed creatures that use breathing systems that diffuse oxygen into tissues (like insects) to get bigger and bigger. However, two things argue against this being the reason for the giant sea scorpion. First, it predates this increase in atmospheric oxygen. And second, this beast was too big to come onto land, so it wouldn’t have even used atmospheric oxygen. So it is unlikely that this atmospheric oxygen boost is the cause of this giant bug. Dr. Braddy speculates that eurypterids grew increasingly large to be better able to prey on armoured fish. Moreover, there was not much competition from vertebrates at that time, and the sea scorpions themselves had no predators. So they could get as large as they wanted. However, eventually these giant bugs had to downsize due to competition from large fish with jaws and teeth. They eventually disappeared from the fossil record during the Permian extinction approximately 250 million years ago, which wiped out 95% of marine species.

Personally, I’m glad that we don’t have insects this large around anymore. If I get the creepy-crawlies from a spider less than an inch in diameter, imagine what I’d do if faced with a scorpion 8 feet long! (On second thought, let's not imagine that. It's too creepy.)