Do hard winters kill more insects? Eric Benson can tell you
Clemson Professor of Entomology Eric Benson writes:
This winter, we have had some pretty cold temperatures in South Carolina. We have had multiple days where nighttime temperatures have been well below freezing across the Palmetto State. On the morning of January 7, it was 9°F at my house, which caused a frozen water pipe in my kitchen. Many of you experienced similar situations. Beyond frozen pipes, freezing temperatures have also made my phone ring.
Invariably, reporters ask, “Will freezing temperatures kill all the insects?”
The short answer is: NO!
While a cold snap or “polar vortex” may kill some individuals and even large groups of insects, most cold-blooded insects will survive. Insects have been dealing with deep freezing temperatures from Mother Nature long before recorded history. In general, insects survive the cold by either 1) avoiding it, 2) making “antifreeze” or 3) by actually freezing.
Many insects can avoid freezing temperature by a variety of behaviors. For example, honey bees will cluster and shiver their bodies, making their hives warm and toasty on the coldest days. Many individual insects will seek shelter in our warm structures, burrow deep into the ground, or find just enough shelter in the natural areas to protect them from the cold. Fire ants and termites are classic examples of insects that will go down into the ground under any frost line, sometimes several feet deep, to survive.
Many insects overwinter in egg or pupal stages, which are more resistant to freezing temperatures than larval or adult stages. But even adult insects can change their blood composition to survive the winter. Many moths and beetles can change proteins in their blood composition during the fall that will lower the temperature at which their blood would freeze (essentially the same principle as antifreeze). For example, some pine beetle larvae can change the freezing temperature of their blood to minus 31°F!
Some insects can produce other proteins that don’t stop their blood from freezing, but instead help control any serious damage from the frosty blood. The woollybear caterpillar, a popular insect in folklore for predicting the severity of the coming winter, actually freezes – without dying – under several inches of leaf-litter or snow as it waits for the spring to pupate and become an adult Isabella tiger moth. The insects’ bodies don’t freeze uniformly; the proteins they produce basically protect essential body tissues.
If you grabbed an insect on a summer’s day in South Carolina and threw it into a freezer, you would probably kill it pretty quickly. However, nature is more gradual and diverse. Insects are survivors and know how to deal with winter temperatures.
Eric Benson is a professor of entomology specializing in integrated pest management and training programs at Clemson University. Benson also teaches general entomology and for over ten years, has hosted a live, call-in program on public radio where listeners can call to ask questions about insects and related arthropods. Benson has research projects on ants, termites, bed bugs and cockroaches.