During our single digit weather a couple of weeks ago my mom commented on how it was good because it would kill some of our least favorite garden pests, she said "at least the cold temperatures will kill some of the insects." I didnt have the heart to tell her that most insects are well-equipped to withstand a deep freeze.
Because insects are generally considered "cold-blooded" and maintain a body temperature that reflects their surrounding temperature many head south for the winter. Those that dont head south may try to get in your house, like the Asian lady beetle (one of which is now crawling up the inside of my kitchen window); or if you are a flea you may spend the winter on a warm-bodied animal like the family pet; and still others may lay eggs and die. Some insects have the ability to hibernate, where they slow their functions down so a minimal amount of energy is needed to maintain bodily functions. Hibernating insects need shelter, like leaf debris and plant material to protect them from winter extremes.
Other insects practice what is called diapause where they completely shut down during the winter. Like some spring bulbs, they also have to go through a period of dormancy triggered by cold temperatures before they can actually awaken again once spring arrives. This survival mechanism, then, would only work for insects that live in certain climates.
Insects need to find appropriate protection for the winter, wherever that may be, but in order to survive around here they still need to lower the water content of their little insect bodies. Purdue entomologist, Tom Turpin explains, "Winterizing for an insect is much like the process we go through to winterize a car. We add anti-freeze to the car. Insects add anti-freeze to themselves. If the liquid in the cooling system of a motor is allowed to freeze, the expansion during the process will break the radiator and hoses. The same is true of the liquid in insects. If it is allowed to freeze, the crystals that form will destroy the cells and tissues of the insect and cause death."
In fact, the compounds that make up car antifreeze and insect antifreeze are very similar. Automobile anti-freeze has glycol in it; insect anti-freeze has glycerol. The compound effectively drops the freezing point of the liquid. This means that the insects little system is shut down for the winter with low moisture content so it wont burst like a frozen pipe. Once an insect has converted its liquid to glycerol it can withstand temperatures below freezing but severe winters will still see a higher insect mortality rate.
If nature allows some insects a little thaw time they can actually snap back into action while the weather permits. Ants, for example, may periodically emerge from their underground abode for a couple a days if the weather is unseasonably warm. They will return once temperatures drop again.
Consistent cold temperatures are actually better for an insect in hibernation or diapause because there is no confusion about the season. The hardest on over-wintering insects (and plants) is the freezing and thawing that often accompanies our inconsistent winter season. Too much fluctuation makes them use up their glycerol reserves so they potentially have a harder time making it until spring.
Once spring rolls around and the air and soil temperatures warm the glycerol in the insects body starts to break down, and as it does it gets replaced with water. Just about the time we head for the garden for spring chores the insects are stretching their legs and reemerging to delight or frustrate us for another season.