Where do all the insects go in cold weather?

Ah, winter has arrived once more and with it comes piles of fallen leaves, colder temperatures, wetter weather and … no insects? Yes, indeed, you may have noticed a distinct lack of insect fauna outdoors during this time of year, but why? Where might these mostly miniature creatures go during the colder part of the year?

The main thing to understand when attempting to solve these questions are that insects are ectotherms, also known as being cold-blooded, which means that their internal body temperatures, much like reptiles, are dependent on the temperatures of their surrounding environment. Therefore, since insects live on every continent on Earth and must deal with a wide array of fluctuating temperatures, most insects have adopted at least one of a number of strategies with which to nullify the potentially debilitating effects of an onset of cold weather. These strategies include: built-in antifreeze, migration, diapause, burrowing and nesting.

Almost all insects come equipped with what can appropriately be termed “built-in antifreeze.” When the temperature surrounding an insect possessing this attribute becomes too cold for it to stand, the composition of its blood, or hemolymph, rather, changes so that the hemolymph keeps flowing and the insect keeps moving.

Another strategy for coping with cold weather is to simply avoid it altogether by migrating from a colder clime to a warmer one. Some species of beetles, dragonflies and moths migrate, but the best-known example of a migrating insect is the Monarch butterfly, /Danaus plexippus/, the brilliant orange and black butterfly that feeds solely on milkweed plants. Monarchs can be seen by many coastal Californians from fall through March on the first leg of a migration that will last four generations.

Diapause is a cold-coping strategy akin to hibernation in mammals. During diapause an insect is essentially metabolically inactive. In this state, which can last weeks to months, the insect does not eat, drink, move or grow. Put another way, the insect ceases to expend energy. An insect detects the onset of winter based on the ratio of sunlight to darkness and then processes this information in order to predict when it should safely enter diapause. Other triggers include dropping winter temperatures and the increasing scarcity of sustenance. An example of a well-known insect that enters diapause is the mosquito.

Two more strategies for fighting the effects of cold weather are burrowing and nesting. Both burrowing and nesting involve finding warm(er) areas in which to spend the winter. Insects that utilize the burrowing strategy, such as earwigs, will often either overwinter in leaf litter, the accumulated junk that covers the ground often around trees, or will burrow underground since the soil is often warmer than the air above. Some eggs and certain immature forms of insects (often larval forms) will do the latter and emerge as either immatures or adults when the above-ground temperatures warm again.

Nesting involves entering a structure of some type, either manmade or living, such as a plant, and spending the winter with its confines. Many insects do this, one example being the Argentine ant, /Linepithema humile/, a small black invasive ant species commonly found in California. In fact, a small army of Argentine ants is currently attempting to reside in my home – though I’m making a valiant, and chemical-free, effort to stop their nefarious overwintering plan.

So, although it may seem as if all the insects have vanished for the winter, as you now know, many are still out there, some far closer than you might wish them.

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Explorit Science Center has two exhibitions running: “Body Blueprints” and “Move It! Science in Action.” Admission is $4 general, free for age 3 and under. The museum is open from 2-4:30 p.m. Tuesday-Friday and 11 a.m. - 4:30 p.m. Saturday-Sunday. Explorit is at 2801 Second Street, Davis. For more information: (530) 756-0191 or www.explorit.org <http://www.explorit.org>