Warm and woolly: Some insects thrive in cold temperatures

As temperatures decrease across North Carolina, you’ve probably noticed that insect activity has also decreased. Insects are not warm-blooded like we are; rather, their bodies fluctuate with the temperatures surrounding them. This is why on sunny days you see more insects flying around or sunning themselves and on cold winter nights you see less and less insects flocking to your porch light. Generally, insects are not active when the temperature drops below 40 degrees. Most insects go into diapause, the insect equivalent of hibernation, during the winter. But when you’re talking about insects, there’s always an exception or two to the rule.

The banded woollybear can freeze and thaw to survive freezing temperatures.Image: Whitney Cranshaw, Colorado State University, Bugwood.org.

Perhaps one of the more amazing stories of insect survival in freezing temperatures lies with the banded woollybear caterpillar. The larvae of the Isabella tiger moth, these caterpillars survive the arctic temperatures by freezing, thawing and eating. They repeat this process over and over until they reach the size and maturity to pupate and change into a moth, a process that can take more than 10 years. While most insects cannot survive freezing temperatures because ice crystals form within the body and cause irreparable internal damages, the banded woollybear has a cryoprotectant in their tissues. That’s basically insect antifreeze!

Another insect that thrives in colder temperatures is the hemlock woolly adelgid. This insect is a major forest pest in North Carolina and has caused the demise of countless hemlocks in our state. It uses straw-like mouthparts to feed on the internal starches of hemlock, slowly killing its host over a span of four to 10 years.

Rather than experiencing diapause like most insects, the hemlock woolly adelgid goes through aestivation, a summer hibernation period. During the dog days of summer, the adelgid remains inactive, attached to its host hemlock tree. It’s not until temperatures begin to drop, usually around October or November, that they awaken, hungry and ready to eat.

The hemlock woolly adelgid begins producing a white, woolly, mass that will eventually surround its body. Image: Kelly Oten, NCSU

Throughout the winter, the hemlock woolly adelgid eats and lays eggs. They produce a waxy, woolly mass that covers their body. Scientists aren’t sure what the purpose of this woolly mass actually is – does it protect them from harsh winter weather? Does it protect them from pathogens that might cause disease? Does it provide a moisture barrier or serve as camouflage? Whatever it serves to do, it does it well. By early summer, the adelgid again goes into aestivation, resting and waiting for the cooler temperatures as a sign for their feast to continue.

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