Every once in a while, an insect surprises us by flying or crawling in our houses in the middle of winter.
We always seem to ask where did he come from? What do Insects do in the winter?
I turned to, Winter: An Ecological Handbook by James C. Halfpenny and Roy Douglas Ozanne to find the answers. There I learned about the amazing abilities of insects to survive the cold.
Insects are essentially, little bags of water. The fluid that fills that bag is called “hemolymph”. Hemolymph is mainly water and transports nutrients for the body, gives support for the organs, maintains pressure and sometimes functions as a defense aid (p.177, Halfpenny and Ozanne).
Insects use migration like mammals and birds but also supercooling like plants. Since insects can not internally heat their bodies (they are “cold-blood”) and their bodies aren’t insulated, other amazing methods are relied on to protect insects from dying due to cold.
Insects have five main strategies to make it through the winter: migration, dormancy, communal behavior, winter activity, and cold-hardiness (physiological escape).
Some insects migrate horizontally, across the face of the Earth. Monarchs migrate horizontally when they fly from North America to Mexico to escape the cold. Some insects migrate vertically moving into high altitudes or down into the ground past the frost line of frozen Earth. Some migrate to the spaces between and beneath the bark of trees or to local protected spots.
Some insects simply stop functioning in the cold, they go dormant and stop all activity. These insects stop their growth and development at a certain life stage. Insects may spend the cold winter as eggs, larvae or pupae depending on the species.They remain in that state until warmer weather and better conditions give them a fighting chance to survive. These insects shelter in leaf litter or out in the open. Galls and Bagworm moth pouches are examples of dormant insects out in the open.
Hives and anthills are busy with activity throughout the winter. The high activity of bees and ants raises the temperature of their communal living space. Thus, they are able to survive deep in a warm space in the Earth with homemade central heating.
Snow fleas, black flies, caddis flies, crane flies, springtails and snow fleas all remain active throughout the winter. The aquatic insects move in the streams that remain open and not frozen. The springtails and snow fleas live in the snow. How do they survive the cold, I couldn’t find out. I don’t know it scientists have figured it out yet. Perhaps, they survive by some form of rapid cold-hardiness (see below).
Cold-hardiness (Physiological escape – body functions)
Lastly, we reach the ability of cold-hardiness. I think this is the most fascinating method of all. It isn’t easy to completely explain in a few short sentences, but the basics center on cooling and chemicals. There are two types supercooling: cold-hardiness and rapid cold-hardiness.
Some insects can super-cool. Insects being small bags of water, they are able drop the temperature of that water, to very low temperatures without the water freezing. This process is called supercooling and has to do with freezing points of impurity-free water. To create impurity-free water, insects rid themselves of waste in their intestinal tract.
Rapid cold-hardiness is the other cold-hardiness method. The way I understand it, this is the method used when temperatures fall rapidly, like overnight. An example would be in polar and Arctic regions where the sun doesn’t set but the temperature decreases quickly as the sun sinks in sky, but not disappearing for the night. The next day the sun rises, air temperature warms and the insects warm up and become active again. Rapid-cooling is triggered by chemicals in the body.
Complexity and Ingenuity
I found the method insects use to survive the cold far more complicated and varied that I had previously thought. Just as hibernation among mammals, reptiles and amphibians is more of a continuum of behavior, insect species could use more than one type of strategy to survive.
See also hibernation