This is scientific American 60 second science. I'm Bob Vershahn.

Most animals are pretty good at avoiding the embarrassing faux-pah of having sex with the wrong species.

But what if you're a millipede under a cramped dark slippery rock

with a dozen or more species all scurrying about looking for love?

Fortunately, the critters evolved a solution, elaborate male gonopods,

literally genital feet, with all manner of branches, bumps, and bristles. And even with

12,000 species of millipedes, no two varieties of

gonopods are exactly the same. So the little arthropods can immediately

tell if they're consorting with the wrong species, convenient not only for the

millipedes but also for biologists. So you just have to pick it up and look at it and

you see up yes that's the species and you can identify it.

That's Milopede researcher Petra Seirvault at the Field Museum in Chicago.

The only problem is, no offense to any male millipedes, the gonopods are tiny. If you look at a millipede, it's not that big to begin with, so you

can imagine their modified legs are even smaller. Now before we go any further you might be wondering who cares

about millipedes let alone their genitals and the answer is not enough of us.

millipedes are believed to be the first land animals lured out of the water by tasty dead vegetable matter on Earth's

primeval shores.

They have been in the business of waste management for four hundred sixty million years,

and that means they are eating rotting vegetation.

That returns the nutrients to the soil and the healthy soil is what we need to grow our food.

But today there aren't enough millipede researchers to determine if

their populations are stable and healthy. In fact, Cyrval says there are thousands of

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