NOVEMBER
2002

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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Check out these books by Tom Turpin:

Flies in the face of fashion

What's Buggin You Now?

 

 

 

11-27-02

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Winter is Nap Time for Insects


Insects don't do winter. The insects that buzzed, flapped and crawled through spring, summer and fall have disappeared. Out of sight, but not gone forever. When warmer temperatures herald the arrival of spring, insects--like the miraculous phoenix--shall rise again!

Insects aren't the only animals that find the winter season difficult in northern latitudes. Many birds just leave and fly south. One insect, the famous monarch, uses this approach to deal with the northern winters. So do some humans, come to think of it.

Other animals prepare for the lean times during the short days and cold temperatures of winter by stocking up on food reserves, mostly by laying on extra fat. While humans don't consciously lay on extra fat, we do sometimes store extra food by canning and freezing produce from summer.

Insects are cold-blooded. That means that their body temperature is roughly the temperature of their surroundings. In general, insects can't function very well in temperatures below 50 F. And temperatures around freezing are lethal to most insects. So winter temperatures generally are impossible for insects.

But with insects, there is a way to survive winter. A few live in close association with warm-blooded animals. Fleas and lice that live on the skin of birds and mammals find the winter temperatures downright cozy on the animal heaters that they call home.

Some insects live in our buildings. These insects, like cockroaches, while away the frigid months of winter in tropical luxury, courtesy of our kitchens, bathrooms and steam tunnels.

Insects survive cold temperatures by changes in their biology. This can be one of two types: hibernation or diapause. Hibernation is also practiced by some other animals and is similar to that in insects. In hibernation, the animal just slows down and goes to sleep. Biological functions are reduced to a minimum, just enough to keep the animal alive. Hibernating animals seek shelter to reduce exposure to the cold temperatures.

One well-known insect that hibernates is the ladybug. While there are many species of ladybugs, almost all of them seek sheltered sites in which to spend the winter. Sometimes such a site is our homes. The ladybugs get into the wall voids and attic spaces hoping for a peaceful winter sleep.

Most animals go into hibernation when the temperatures decline and wake up when the temperatures rise. Unfortunately for those of us who find ladybugs hibernating in our attics, that warm-up tends to be all winter long. Heat from the living quarters seeps into the places where the ladybugs are snug as bugs in rugs and suggests the arrival of spring.

Many insects spend the winter in diapause. Diapause is similar to hibernation except that the insect that goes into diapause will stay in that condition until it is subjected to a period of very cold temperatures. Following such a period, warming temperatures will cause the insect to become active and continue development.

Most insects that hibernate do so as adults. Insect diapause, though, shows up in several stages. Some insects are in diapause in the egg stage. The eggs hatch when spring comes. Other insects show diapause in the pupa stage and emerge as adults when winter is over. Still other insects spend the winter as diapausing larvae. They then form the pupal stage when the winds of winter blow over.

In all cases, when the insect is in an overwintering state, it must keep from freezing. The secret is antifreeze. Just like humans use antifreeze to winterize the car radiator, insects use it to keep their tissues from freezing. After all, it doesn't do any good to take a long winter's nap if you don't wake up to smell the spring flowers.

 

 

Writer: Tom Turpin
Editor: Olivia Maddox