OCTOBER
2007

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

10-11-07

Where Have the Insects of Summer Gone?

In his poem "On the Grasshopper and Cricket," British poet John Keats wrote, "when the frost has wrought a silence." Keats was referring to the time of year when insect activity comes to a screeching halt in temperate regions of the world. The arrival of winter.

Cold-blooded insects don't do winter. In an active state anyway. Unless they manage to live or find their way into our homes. Or schools. Or factories. Places where we keep the temperature artificially warm during the cold days of winter. Keats put it this way, "from the stove there shrills the cricket's song."

Most insects face the winter outdoors. American poet Aileen Fisher says:

"None has the least little

urge to know

what the world is like

when the sky says, 'Snow.'"

We do know that insects somehow survive the winter. After all, when the weather warms up next spring, the teeming hoards of these six-legged creatures will show up again. As they have for millions of years. So how do they manage to survive the cold?

Some don't. These species are generally known as spring invaders. Populations of these insects survive the winter months in climates in the south and return next spring when temperatures are suitable for their survival. Generally, they come into temperate regions, carried by weather fronts that bring our spring rains.

One well-known insect, the monarch butterfly, migrates to a suitable location in the mountains of Mexico where it spends the winter. As the temperatures warm in spring, these butterflies head north. Along the way, the butterflies lay eggs on milkweed plants where their caterpillars feed. Some make it into Canada. First or second-generation offspring of the northward-bound monarchs do the south-of-the-border trip to Mexico for the species annual winter siesta.

Most insects though just batten down the biological hatches and endure the cold and freezing days of winter. These insects have ways to avoid freezing to death. In general, the process is known as winterizing. The process is very similar to what we do with our cars to keep the cooling system from freezing during the winter. We add antifreeze, a chemical that functions to lower the freezing point of the liquid coolant.

Scientists divide the approaches used by insects for winter survival into two categories. The first is hibernation. Much like the hibernation process of other animals, adult insects just slow down biological processes in the body and enter into a sleep-like state. Like hibernating mammals, hibernating insects seek some shelter to provide some protection from the cold. That is why ladybird beetles, boxelder bugs, and some types of flies and wasps end up in our homes as winter approaches.

In general, hibernating animals wake up and begin moving around when the temperature warms up. For that reason, hibernating ladybird beetles become active when temperatures in their hiding places warm up. Consequently, these insects are likely to be seen crawling around on cold winter days in the warmth of our homes. Sometimes to the dismay of a homeowner who was expecting a long winter nap free of insects!

Many insects enter into what is known as diapause. Diapause is defined as a state of arrested development in which an insect is able to survive a period of unfavorable conditions. Such as winter. Like in hibernation, the tissues are protected with antifreeze. Unlike hibernation, diapause exists for a period of time regardless of temperatures that may occur. So insects can't just come out of diapause when temperatures warm up.

Hibernation occurs with adult insects. Diapause occurs in different insect stages. For instance, corn rootworms spend the winter in diapause in the egg stage and corn borers in the pupa stage. When spring comes, both will continue development for another year.

So during the winter, the insects are there. They are just snoozing away the cold days of winter. Sounds like a good plan to me!

 

Writer: Tom Turpin
Editor: Olivia Maddox