Parasitic Wasp Species May Outnumber Beetle Species Beetles make up around 40% of all insect species ever described and around 25% of all animals. Are there really that many different kinds of beetles, or do scientists have a strong pro-beetle bias?

Beetles And Wasps Vie For Title of Most Diverse Critter

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LEILA FADEL, HOST:

When a famous biologist named J. B. S. Haldane was asked what science had revealed about God, he said that the creator apparently had an inordinate fondness for beetles. That's because there are just so many different kinds of beetles. Named species make up about a quarter of all known animals, and new ones are being discovered all the time. But as NPR's Nell Greenfieldboyce reports, there's another contender competing for the title of most diverse critter. First, the case for the beetle.

NELL GREENFIELDBOYCE, BYLINE: A beetle is an insect with a hard wing case. There's ladybugs and scarabs and stag beetles and jewel beetles and whirligig beetles and on and on and on. Don't even get me started on the beetles known as weevils. There's around 400,000 known species. That's like 40 times the number of bird species. And this mind-boggling variety is part of the fascination for Rachel Smith.

RACHEL SMITH: It's kind of akin to, like, early humans looking up into the sky and, like, gazing at this, like, vast unknown. But we have this vast unknown here on Earth with, like, this crazy diversity of beetles that seemingly never ends.

GREENFIELDBOYCE: Smith is about to graduate from the University of Kansas, and she recently had a research job on campus. She was handed a bunch of water beetles that had been collected in South America, and she was told, sort through them, see if there's anything new.

SMITH: I had about 2,000 specimens that I sorted through and came up with these 18 new species.

GREENFIELDBOYCE: Eighteen new species, all brown, oval-shaped and very small.

SMITH: The average size of these beetles is probably about the size of a capital O in size-12 font.

GREENFIELDBOYCE: So teeny-tiny. To tell the difference between them, you need a microscope.

SMITH: And really, it came down to - this is going to sound funny, but it came down to the morphology of the male genitalia.

GREENFIELDBOYCE: Plus genetic differences. Now, it takes a lot of devotion to patiently examine the genitalia of tiny brown beetles. And beetles seem to inspire that kind of dedication. Charles Darwin loved beetles, and he had plenty of company. One of Napoleon's generals had one of the largest collections in the world.

ANDREW FORBES: Collecting beetles was a hobby in the 1800s. People would go out and collect as many beetles as they could and then, you know, get together and compare the size of their beetle collections.

GREENFIELDBOYCE: Andrew Forbes is an evolutionary biologist at the University of Iowa. He says, OK...

FORBES: And it's certainly true that there are more species of described beetles than any other kind of animal.

GREENFIELDBOYCE: He says maybe that's because 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.

FORBES: These are these tiny, little wasps that lay their eggs in other insects.

GREENFIELDBOYCE: He says the larva consumes the host from the inside.

FORBES: Eventually, it will kill the host, and it bursts from the host's body kind of like Ridley Scott's "Alien" - you know, like this horrible thing.

GREENFIELDBOYCE: He says these wasps are incredibly diverse with around 100,000 known species, but way more species are unknown. In fact, Forbes and some colleagues recently looked at 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.

FORBES: Our numbers tell us that there are very likely more species of these wasps than any other type of insect.

GREENFIELDBOYCE: Including beetles. Oh, that's a bold claim, but studies in the field support it. Lynn Kimsey is an entomologist at the University of California, Davis. She spent years doing intensive studies of all the insects in different environments, like, say, some desert dunes in California and in Indonesian rainforests. She says, in each place, parasitic wasps beat out beetles.

LYNN KIMSEY: So you have to figure that for every species of beetle, there are probably at least one or two wasp parasites or parasitoids.

GREENFIELDBOYCE: That is 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.

DENA SMITH-NUFIO: I just think they're fascinating and beautiful (laughter). So I'm going to be like the other people who root for their own little group of insect and say, well, of course the beetles are fantastic, and they're special and they probably are the most diverse group (laughter).

GREENFIELDBOYCE: In all seriousness, she thinks a friendly wasp-versus-beetle smackdown is good for science.

SMITH-NUFIO: I think it just keeps the whole endeavor rolling. Personally, I find it a lot of fun.

GREENFIELDBOYCE: And, of course, there are other critters out there, like mites and worms, that could be even more diverse, but they might not have as many fans as beetles or even wasps.

Nell Greenfieldboyce, NPR News.

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