Some insects have quite the sweat tooth

SCOTT SIMON, HOST:

This summer, NPR Science Desk is celebrating sweat. Boy, do they know how to have a good time. Perspiration is vital. It keeps humans cool and comfortable, including B.J. Leiderman, who writes our theme music. But it turns out our sweat is essential to other animals, too. NPR's Geoff Brumfiel has more on little critters that seek out our sweat.

GEOFF BRUMFIEL, BYLINE: Many insects survive by pollinating flowers, but there's one thing flowers can't give them - sodium.

SAMUEL RAMSEY: Sodium is really important for reproduction in insects. But when you're feeding constantly on only nectar, you don't have a lot of options.

BRUMFIEL: Samuel Ramsey is an entomologist at the University of Colorado at Boulder. Sodium is a component of salt, and salt is found in animals' body fluids including human sweat. All over the world, there are species of bees and butterflies that go for sweat. If one of them pays you a visit, well, don't be scared. They're gentle creatures.

RAMSEY: It behooves them to be as nice about this as possible.

BRUMFIEL: In fact, many bees that feed off sweat don't even have stingers. They just want to lap up a tiny bit of salty perspiration without bugging you too much. Ramsey says, let them.

RAMSEY: I mean, what are you going to do with your sweat? You're getting rid of the stuff. I mean, at the end of the day, they're just trying to take care of something that you're not going to use anyway.

BRUMFIEL: It's one of those cases in nature where it doesn't hurt to help out a stranger.

RAMSEY: The relationship that they currently have when they're feeding on your sweat is called a commensal relationship. You don't lose anything in the process, but the organism initiating this is gaining in the process.

BRUMFIEL: But here's the thing about evolution. You give it even a tiny inch, and they'll find a way to take advantage of you. So I've just come back from a jog. I'm completely covered in sweat and mosquitoes.

RAMSEY: Mosquitoes are very attracted to human sweat.

BRUMFIEL: It turns out that it's probably not a coincidence. In fact, Ramsey says some entomologists believe mosquitoes could have evolved from sweat-eating insects.

RAMSEY: We think that it's very possible that they were from a group of flies that were interested in consuming some of the sweat and, as they evolved, were able to eventually pierce through the skin and get at this resource that has a lot more nutrients than the sweat itself.

BRUMFIEL: That resource being your blood. So to sum up, your sweat is essential not just to you, but to a host of little insects that needed to do cute, little insect things like pollinate flowers. Be nice. Except for mosquitoes; you can keep killing them. Son of a - ugh.

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BRUMFIEL: Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.