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Beetles And Wasps Vie For Title of Most Diverse Critter

There is a seemingly never-ending variety of beetles, about 400,000 known species!
There is a seemingly never-ending variety of beetles, about 400,000 known species!

It's unusual for a college student to discover even one new species. Rachel Smith discovered eighteen. All of them were beetles.

That means that the stupendous, ever-growing list of beetle species just got a little longer. About 400,000 beetle species are known to science—that's around a quarter of all known animals. It's little wonder that famous scientist J. B. S. Haldane reportedly once said that if there's a God, the Creator seems to have "an inordinate fondness for beetles."

But there's another contender out there that some scientists say should get the title of most diverse critter: parasitic wasps.

First, consider the case for beetles—insects that are known for their hard wing case, after all. Their mind-boggling variety is part of the fascination for Smith.

"It's kind of akin to early humans looking up into the sky and gazing at this vast unknown," says Smith, "but we have this vast unknown here on Earth with this crazy diversity of beetles that seemingly never ends."

Smith, who is about to graduate from the University of Kansas, recently had a research job on campus. She was handed a bunch of water beetles that had been collected in South America, and was told to see if any looked new to science.

"I had about 2,000 specimens that I sorted through," she says, noting that all were brown, oval shaped, and very small. "The average size of these beetles is probably about the size of a capital O, in size 12 font."

To tell the difference between them, she needed a microscope. "Really it came down to--this is going to sound funny--it came down to the morphology of the male genitalia," says Smith.

It takes a lot of devotion to patiently examine the genitalia of teeny tiny beetles, but beetles seem to inspire that kind of dedication. Charles Darwin loved them, and he had plenty of company. One of Napoleon's generals had one of the largest collections in the world.

"Collecting beetles was a hobby in the 1800's. People would go out and collect as many beetles as they could, and then get together and compare the size of their beetle collections," says Andrew Forbes, an evolutionary biologist at the University of Iowa.

"It's certainly true that there are more species of described beetles than any other kind of animal," he says. But maybe that's because people have spent so much time hunting for them and cataloging them.

Plus, beetles tend to be relatively easy to find and charismatic. At least, they're more charismatic than the kind of insect Forbes likes to study: parasitic wasps.

"These are these tiny little wasps that lay their eggs in other insects," he says, explaining that the larva consumes the host from the inside. "Eventually, it will kill the host and it bursts from the host's body kind of like Ridley Scott's Alien, you know, this horrible thing."

Around 100,000 parasitic wasp species are known, but way more are unknown. In fact, Forbes and some colleagues recently studied a variety of different insects and the wasps that parasitize them, to come up with an estimate of how many wasp species would be expected to be out there.

"Our numbers tell us that there are very likely more species of these wasps than any other type of insect," he says.

That's a bold challenge to beetle's claim to fame, but studies in the field support it.

Lynn Kimsey, an entomologist at the University of California, Davis, has spent years doing intensive studies of all the insects in different environments from desert dunes in California to an Indonesian rainforest. In each place, she says, parasitic wasps beat out beetles.

"You have to figure that for every species of beetle, there are at least one or two wasp parasites or parasitoids," she says.

Still, that can be a tough one for people who love beetles to accept. Dena Smith-Nufio of the University of Colorado has studied beetles, including fossilized beetles, to try to understand what drove their intense diversity.

"I just think they are fascinating and beautiful," she says, and then jokingly adds, "so I am going to be like the other people who root for their own little group of insects and say that, 'Of course, the beetles are fantastic and they're special and they probably are the most diverse group.' "

In all seriousness, she thinks a friendly wasp versus beetle smackdown is good for science. "I think it just keeps the whole endeavor rolling," says Smith-Nufio. "Personally, I find it a lot of fun."

There are other creatures out there, like mites and worms, that could be even more diverse. But they might not have as many fans as beetles--or even parasitic wasps.

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