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As Americans try to plan for the future, animals are just trying to get through the winter, and they have several options. They can head south to a vacation home or timeshare in, say, Florida or Mexico, or they can bundle up and go about their business. Or they can hang a do-no-disturb sign on the door of their caves and hibernate until spring. And we all know that's what bears do. As NPR's Joe Palca reports, mosquitoes do it, too.

JOE PALCA: Technically speaking, mosquitoes don't hibernate, although if you really want to get technical about it, some scientists say bears don't hibernate, either. They just go into a kind of deep, winter sleep.

But getting back to mosquitoes, what they do do is go into a state called diapause. David Denlinger says it's a state where mosquitoes...

Professor DAVID DENLINGER (Entomologist, Ohio State University): ...essentially shut down their development and just hunker it out until spring comes.

PALCA: Denlinger is an entomologist at the Ohio State University in Columbus. He studies a common backyard mosquito called Culex pipiens. Not all Culex pipiens make it to spring.

Prof. DENLINGER: The males die, and only the females overwinter.

PALCA: And like bears, the females start storing fat as winter approaches.

Prof. DENLINGER: They have a structure we call the fat body that's much like the liver of mammals, and much of the fat ends up in that structure, although it's there in also in their blood and other tissues, as well.

PALCA: And we're not talking just a smidge of fat.

Prof. DENLINGER: Females that go into diapause probably have 10 times the fat accumulation that a non-diapausing mosquito has.

PALCA: That's a fat mosquito. Culex pipiens isn't the only insect Denlinger studies. He's interested in how all cold-blooded insects make it through harsh winters.

Prof. DENLINGER: We were sitting around one day and thought, you know, we really should push this to the limit sometime.

PALCA: So Denlinger and some colleagues mounted an expedition to Antarctica.

Professor RICK LEE (Miami University): There is one insect that is endemic to that continent, it's found only there: a wingless fly, of all things.

PALCA: That's Rick Lee from Miami University in Oxford, Ohio. He was on the Antarctic expedition. The wingless fly - or midge, as some call it - is the only insect species to survive in Antarctica through the ages. And it has some amazing strategies.

Prof. LEE: First, it retains its capacity to survive being frozen solid.

PALCA: Lee says it does this by making sugars and sugar alcohols that protect cell membranes.

Prof. LEE: They also produce something called heat-shock proteins.

PALCA: These are special molecules cells usually only make when they're under severe distress. The midges appear to make them all the time. And the midge has one more trick up its sleeve.

Prof. LEE: It can also tolerate severe dehydration.

PALCA: We're talking really severe dehydration. In the larval stage, it can lose most of its body water.

Prof. LEE: These little larvae look like raisins when you dry them out like this. They look terrible. They look for sure that they would be dead. You put them in water, they plump up, and they wiggle away.

PALCA: Of course, it's not much of a life, being a flightless midge in Antarctica. They spend two years in this raisin stage. Then in the summer...

Prof. LEE: ...the adults emerge. They mate and lay their eggs, and probably only live about 10 to 14 days.

PALCA: Seems like a lot of work for not much reward, but Lee says for any species, there's really only one requirement for success.

Prof. LEE: Whether you can reproduce and leave offspring. That's the bottom line.

PALCA: An appropriate thought as we head towards spring.

Joe Palca, NPR News, Washington.

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