Tag Archives: caterpillar

Winter survival

Hi all! Great to be back after a little hiatus.

Given the weirdly fluctuating outdoor temperatures so far this year, I have been contemplating the myriad of ways in which animals survive the winter. In pursuit of more knowledge, I pulled Bernd Heinrich’s Winter World: The Ingenuity of Animal Survival off of the shelf, and, even though I am only a couple of chapters into it so far, have already learned several interesting tidbits.

Snow fleas (Hypogastrura nivicolautilize) utilize anti-freeze to stay alive in the snow. Photo by Daniel Tompkins via Wikimedia Commons
Snow fleas (Hypogastrura nivicolautilize) utilize anti-freeze to stay alive in the snow. Photo by Daniel Tompkins via Wikimedia Commons.

For instance, some insects survive winter because their bodies contain substances, similar to antifreeze, that lower the freezing point of water. (As a side note, some types of deep water fish contain a similar type of “antifreeze”, the gene for which is now being used to prevent ice cream from getting freezer burn. Yoiks!)

Even more astonishing than having antifreeze-filled bodies is the fact that some insects have the ability to separate the freezing and melting points of water (!!) in a process called “thermal hysteresis”. Think about that for a minute: generally, the temperature at which water goes from a solid state (ice) to a liquid state (water) is 0 degrees Celsius/32 degrees Fahrenheit. However, the process of thermal hysteresis allows these insects to exist in a “supercooled” state (below 0 degrees C but without freezing) and thus survive cold winter temperatures without dying. This supercooled state, however, is highly unstable, and the introduction of any foreign molecule will cause the entire system to break down and freeze almost instantly. Life is so amazing, and so fragile!

Additionally, some insects can utilize a process called “diapause”, which could be loosely defined as a type of “arrested development”. Many moths, for instance, live as pupae through the winter in a diapausal state.  (A common example is the type of yellowish, fuzzy tent caterpillar cocoon that you sometimes find attached to the underside of a log in a woodpile.

by NobbiP via Wikimedia Commons
A woodpile is a great place to look for overwintering insects. Photo by NobbiP via Wikimedia Commons.

These pupae, which are waiting until spring to hatch into moths, are in a state of diapause. (Naturalist’s note: not all fuzzy, pale-colored cocoons are those of tent caterpillars; you may need to do further research if you wish to correctly identify any particular species.)

The phenomenon of diapause is not limited to winter months, however; some adult insects will enter a reproductive diapausal state in the summer when migrating or searching for host plants. In fact, some types of insects, in the adult phase, do not even have mouth parts, as they quickly breed and lay eggs before dying without eating anything at all. I am not sure if this evolutionary phenomenon counts as diapause or not; perhaps biologists refer to it as something else altogether.

By Stephen Lody via Wikimedia Commons
Adult polyphemous moths (Antheraea polyphemous) have only vestigal mouthparts. Photo by Stephen Lody via Wikimedia Commons.

Anyway, the next time you are outside this winter, check under logs, rocks, or dead leaves to see what kinds of insect life you can find, waiting until next spring to re-emerge. If you want to learn more about what kinds of creatures you are likely to discover, see here for what one biologist found in her woodpile in Ontario. (Note that the author of that blog is also a co-author of the new edition of the Peterson Field Guide to Moths of Northeastern North America Happy exploring!