Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
12/14/98
Contacts:
Donald Lewis, Extension Entomology, (515) 294-1101
Elaine Edwards, Extension Communication Systems, (515)
294-5168
Yard and Garden Column for the Week Beginning Dec. 18.
Butterflies in Winter
By Donald Lewis
Extension entomologist
Iowa State University
It's a cold, cruel world out there in the landscape this time of the year. And delicate, cold-blooded creatures such as butterflies face a formidable challenge just to stay alive through one of nature's most inhospitable periods, winter on the Great Plains.
But butterflies and other insects do survive, and have been doing so for a long, long time. In fact, it is not too difficult to believe that insects are better equipped for this frigid time of year than our own species.
Insects, like snakes, frogs and turtles, are cold-blooded. Their body temperature rises and falls with the temperature surrounding them. This is the opposite of what people and other warm-blooded animals do. We maintain a constant, warm body temperature through all extremes with elaborate energy-using tricks to warm us when the world is cold, and to cool us off when it is hot.
Cold-blooded animals such as insects fight no such temperature-regulating battles. Their body temperature is hot in the summer and cold in the winter. This adaptation (go with the temperature flow) allows them to survive the winter with seeming ease.
There is a down-side to the cold-blooded lifestyle. At cold temperatures insects become inactive and exist in a state of dormancy similar to "suspended animation." During the cold-induced dormancy period, an insect cannot eat, grow, develop, reproduce or even move around. Dormancy is an adaptation that improves the chances of surviving until warm temperatures return.
Each insect species has a range of temperatures suitable for activity. When an insect is either too hot or too cold it becomes dormant. It is active only at temperatures between the two extremes. As a rough rule-of-thumb, insects are active between 45 and 100 degrees F.
Where Do Butterflies Go?
To understand how an insect such as a specific kind of
butterfly survives the winter, it is necessary to think
about the life cycle. Butterflies have a complete life cycle
of four stages: egg, caterpillar, chrysalis and
adult.
For most species of butterflies, only one stage is adequately equipped (that is, programmed or prepared) to last through the winter, although it can be a different stage for different species. For example, swallowtail butterflies overwinter in the chrysalis stage attached to the plant foliage where the caterpillar fed. The white cabbageworm butterfly and the related orange sulphur butterflies also winter as a chrysalis. The viceroy and the checkerspot, on the other hand, survive as partly grown caterpillars.
Only a few butterflies can make it through an Iowa winter in the adult stage. These include the fritillary, the mourningcloak, the painted lady and the red admiral.
The most famous butterfly, the monarch, doesn't stay in Iowa for the winter at all. Monarchs leave in the fall and migrate to central Mexico to spend the winter. The monarch must be re-introduced into the state every spring by north-bound dispersal of last year's butterflies and their offspring.
Why Don't They Freeze to Death?
The overwintering stages of insects are equipped with
one or more "tricks" that increase the chances of survival.
One is the hiding behavior seen in the fall. Insects that
were active just a few short weeks ago didn't all die. Some
went into hiding and are concealed under loose bark, leaf
litter, rocks or debris. Others are a few to several inches
deep in the soil.
A more important preparation that takes place in the fall involves subtle changes in body chemistry. Many insects reduce the water content of their bodies and produce glycerol and other protective compounds that lower the freezing point of the body fluids. These natural antifreeze compounds essentially "winterize" the insect in preparation for below-freezing temperatures.
So, Do Butterfly Boxes Work?
Butterfly boxes also are known as butterfly roosts and
hibernation houses. Advertisements claim these bird
house-sized structures will encourage butterflies to stay in
your garden by providing necessary shelter. It is tempting
to dismiss these well-intentioned accessories as worthless,
but that's not quite true. They can be an attractive and
artistic addition to the garden and they also announce to
visitors (that is, people) your intentions to have a
butterfly-friendly place.
But the butterflies couldn't care less. Several studies show that the boxes are virtually never used except by spiders, wasps and mice. The few butterflies that do remain for the winter appear to find sufficient natural hiding places under dead leaves, twigs and wood piles, where they hang upside down with their wings folded together.
The best encouragement for butterflies is to diversify your landscape. Plant a wide variety of flowers and plants that are attractive to butterflies and that will feed the hungry caterpillars. And remember to reduce insecticide use as much as possible.
ml: isugarden
Extension programs are available to all without regard to race, color, national origin, religion, sex, age, or disability.