ENHS Nature Trails Oct. 97 Article 2

President's Column: The Iceman Cometh: Where insects go in winter
by Nathan Tublitz

You're a ladybug, it's summertime and the living is easy. You spend your days languidly hanging out on your favorite plant, catching the rays, and feasting on those deliciously plump, juicy aphids. But the dog days of summer don't last forever. As autumn approaches, the days get shorter and you start to wonder how you're going to get through the frosty Oregon winter. Falling day and night time temperatures raise a cuticle-tingling chill in your blue-green blood as you realize that a lack of preparation for the coming winter means certain death. Oy vey, vhat to do?

This scenario, minus the eastern European accent, is enacted and re-enacted billions of times each fall by the insects inhabiting our wonderous Pacific Northwest. Except for a few unusually well adapted species, our local insects are unable to contend with winter's harshness, even in the relatively mild climate of the Willamette Valley. So what must a poor bug do to survive? (By the way, the word "bug" is used generically by non-experts as a synonym for all insects whereas professional entomologists use this word only in reference to a specific taxonomic group of insects, the order Hemiptera).

Contrary to the opinions of the bug-haters of this world, insects haven't survived on our fair planet for the last 500 million years because of a lack of flexibility. Their incredible adaptability is particularly pronounced in this instance where insects ave evolved not one but three different strategies to overwinter successfully. The majority of insects make it through winter by stopping their development and remaining in a particular stage for the entire winter season. This process, known as diapause, is an adaptation that enables an insect to survive regularly occurring adverse conditions. In temperate regions like here in the Pacific Northwest, diapause is a consequence of the need to last through cold winters when normal growth is impossible. Different insect species diapause at different stages during their life cycles: many moths and butterflies (order: Lepidoptera) diapause in the pupal stage while others overwinter as eggs, caterpillars (larvae) or even adults. Most beetles (order: Coleoptera) for example spend their winters underground as diapausing adults.

Diapause is not the only strategy used by insects to endure the long winter. Like the elderly of our own species, many insect species choose to avoid the cold by migrating to warmer and sunnier climes. Some species travel great distances each fall; the 1000+ mile migration of the Monarch butterflies is an amazing physiological and metabolic tour-de-force. How these lovely butterflies navigate over such distances and successfully find their winter nesting sites remains one of the great unexplained biological mysteries.

The third strategy employed by insects to circumvent the hazards of winter is group nesting. Most often employed by colonial insects such as bees, yellow jackets, and ants (order: Hymenoptera), this strategy consists of building nests, either above or below ground, to house large numbers of individuals. These nests serve as the primary base of operation during the winter and most often contain large food stores to allow the nest's inhabitants to avoid exposure to potentially fatal winter storms. The activity in a winter nest can be hot and heavy, as individuals tend to such housekeeping chores as nest repair, food distribution, and maintenance of the young. This activity keeps the nest buzzing and at a very pleasant temperature, often 75 degrees F or warmer.

But what about those lovely ladybugs (called ladybirds in Britain)? In mid autumn (right about now), ladybugs take flight from the fields and meadows they inhabited all spring and summer and literally head for the hills. The end point of this short migration is usually a cave or protected ledge where 10's of thousands of adult ladybugs form huge aggregations for the purpose of getting through the winter. Come spring, the ladybugs migrate back to lowland meadows and fields. It is interesting to note that ladybugs frequently use the same caves as their winter hideaway year after year. How they know which cave to use and where they are located remains another of life's intriguing mysteries. Especially intriguing is the fact that the adults who fly off to the caves in the fall are the grandchildren or great-grandchildren of the adults that left the same caves the previous spring. Who told the offspring where to go?? Food for thought. Maybe one of you will unravel these wonderful mysteries.

One final point and gardeners please take note: ladybugs purchased at your local garden shop in the spring undoubtably were collected at the overwintering site in the hills. These bugs when exposed to warmer spring temperatures have an innate urge to migrate, quite reasonable considering that they still think they're in the hills. However, instead of being in the hills they have been placed in your garden where you are hoping they will munch on those pesky aphids. Unfortunately, innate migratory urges override their hunger, forcing them to take off for places other than your garden. Thus, if you want ladybugs to stay at your place, convince your neighbors buy a whole bunch.

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