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What Do Insects Do in Winter?

When winter comes, most bugs either migrate or time travel. But some get far more creative

The woolly arctic moth caterpillar produces alcohols that allow it to avoid freezing at temperatures reaching -70 degrees F. (Christina Rollo / Alamy Stock Photo)
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We humans survive the icy throes of winter with warm coats, space heaters and hot chocolate. Insects, however, have a few more creative strategies up their sleeves. Whether it’s special proteins that act like the antifreeze in your car, body fluids spiked with alcohol instead of water or gearing up for long-distance travel to warmer climes, it seems that these hardy bugs have developed their own answers to the biological problems winter poses.

You’ve likely heard of one the most common ways insects make it through this darkest and coldest season: time travel. "Either they escape in space, which means they migrate, or they escape in time, which means they become dormant," says Scott Hayward, an invertebrate biologist at the University of Birmingham. "The vast majority actually becomes dormant."

To survive the wintertime shortage of food and warmth, mammals like bears and chipmunks tend to hibernate. While hibernation is often thought of as a deep sleep, it’s actually a biologically distinct state of dormancy: Hibernating animals stock up on food and reduce their metabolisms through processes that aren’t still fully understood. NASA researchers are even looking into techniques that could induce hibernation in humans, to help astronauts make it through years-long space journeys.

Insects have their own version of this powerful tool: diapause. Similar to hibernation, insects preparing to enter diapause will usually try to seek some kind of shelter from the cold, says Hayward, who has done extensive research on insect dormancy and survival in extreme environments. That often means burrowing underground (consider the fact that, in winter, hundreds of insects might be lying dormant just inches beneath your feet), but can also mean finding shelter in trees trunks or under rocks.

Some insects, like the European corn borer, have managed to frustrate farmers and intrigue entomologists by finding ways to live aboveground in the winter. This notorious corn pest boasts an extreme tolerance for cold, even more so than hibernating species. Studies have found that borer larvae can even survive being supercooled for several minutes to -40 degrees F. The borer balls up within corn stalks or corn cobs, and is able to survive even when the water inside its body (though not within its cells) freezes.

Other insects stock up on the antifreeze. In Antarctica, the flightless Antarctic midge produces large amounts of sugars in its cells, which lower the freezing point of liquids. Simultaneously, the midge allows the freezing soil around it to draw out nearly every drop of water in its body. "The insect becomes completely dehydrated," Hayward says. "Then, it can't freeze." This helps the miniscule bug—which is both the only insect and the largest land animal on that continent—resist freezing altogether.

The arctic woolly bear moth spends roughly 90 percent of its life in a frozen state. The moth caterpillar also accomplishes this feat by producing sugar—specifically, the alcohol glycerol. In the same way that vodka can be stored in the freezer and remain liquid, these liquids don’t freeze, preserving the tissues of the moth larvae and allowing it to survive at temperatures dipping down to -70 degrees F. The Alaska Upis beetle can withstand temperatures reaching down to a shocking -100 degrees F, by producing a special “antifreeze molecule.”

But the majority of insects aren't so tenacious. Around - 30 degrees F is a typical limit for many species, Hayward says. That’s why many insects have ranges limited to more tropical areas of the world that never experience freezing temperatures, like the bug-ridden Amazon or mosquito-rich countries in Africa, South America and Asia.

European corn borer larvae can survive the winter frozen inside stalks of corn. (WILDLIFE GmbH / Alamy Stock Photo)

Global warming, however, may soon change that maxim and threaten insect populations around the world. As the Earth warms overall, insects are shifting toward the poles to colonize areas that are warmer than before in the summer months. Yet many of these insects lack the ability to survive the colder winters found in these regions.

"Where they can't do that, they can't become established," Hayward says. Meanwhile, toward the equator, warmer temperatures are disrupting other insects’ diapause cycles.

Though diapause is an adaptation to survive the winter, temperature is not the main factor that triggers it. Instead, shorter days in the lead-up to winter help signal to the insects' bodies that it's time to get ready for dormancy. As the days stay warmer later into the fall, insects' bodies get confused. Mistakenly thinking that it's spring or summer, they often end up aborting the diapause process to begin looking for food or mates—which leaves them unprepared for when winter actually strikes, Hayward says.

Why should humans care? Consider the well-known plight of bumblebees, a vital pollinator for many species of plants and agricultural crops. Already struggling against habitat loss and pesticides, bee populations are now also battling changing seasons. Warming temperatures cause not only later autumns, but also earlier springs, which can confuse one very important member of the hive: the queen.

Queen bees are the only hive inhabitants that typically enters diapause. They typically awaken once a year, in spring, and leave to forge a new colony. But with spring often starting earlier, however, hives are reaching the size at which a new queen will be born and attempt to found a new colony before the winter has begun, rather than at the start of spring. Their offspring are then left struggling to find flowers to feed on in the dead of winter, and must deal with temperatures they have not evolved to handle.

"You've got massive levels of mortality," Hayward says, "and you've [then] got fewer pollinators the following year."

There are myriad other ways that insects have developed to beat the cold. But when the going gets tough, some insects don’t get tougher—they just leave. The monarch butterfly, for instance, is well-known for its colorful and awe-inspiring wintering strategy: taking hundreds and hundreds of its best friends and heading thousands of miles toward the equator to avoid cold temperatures.

"There are really an unbelievably diverse number of ways they survive winter," Hayward says.

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