In the Garden: Bugged by the Cold?
During some single-digit weather this winter season, a friend commented on how it was good because “at least the cold temperatures will kill some of the insects.” I didn’t have the heart to tell him 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, some head south for the winter. Those that don’t 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. Still others may lay eggs and die.
Some insects, however, have the ability to hibernate. They slow their functions down to the minimal amount of energy needed to maintain bodily functions. Hibernating insects need shelter, like leaf debris and plant material, to protect them from winter extremes.
Ticks, for example, begin to freeze at 7 to 14° F, depending to radiate heat as they huddle on the species, but they can offset this vulnerability by seeking refuge under leaf debris that can naturally maintain a temperature near 28°. Think about all those insects that lurk under the wood pile as they seek shelter from the cold … it may not be as cold there as you think, after all! Even more amazing is honey bees’ ability to warm their hive. The worker bees will shiver around their queen. Apparently, a healthy colony can warm the hive to 90° F even in cold weather. If you are not hiding in the wood pile or shivering in your colony you may be one of those insects considered “freeze tolerant,” a trait that depends on a process called diapause.
Diapause allows an insect to completely shut down during the winter. Like some spring flower bulbs, they also have to go through a period of dormancy triggered by cold temperatures before they can actually awaken again in spring. This survival mechanism was adapted by insects that live in certain climates that see extreme changes in temperature.
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 antifreeze to the car. Insects add antifreeze 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 antifreeze has glycol in it; insect antifreeze also contains glycerol. The compound effectively drops the freezing point of the liquid. This means that the insect’s little system is shut down for the winter with low moisture content so it won’t 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 of days if the weather is unseasonably warm. They will return once temperatures drop again. A walk in the Parklands on a warm winter day proved this to be true as the birds were chirping and the gnats were flying about on the trail in late December!
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 insect’s body starts to break down. 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.
Jeneen Wiche teaches at the University of Louisville and raises Kentucky-grazed lamb, poultry and eggs at Swallow Rail Farm in Shelby County with her husband, Andy Smart