What happens to insects during the winter months?
Our weather is a common topic of conversation here in Atlantic Canada. If you don’t like the weather, wait a few minutes and it will change, has been a constant joke for generations. This winter is another unusually warm one overall with less snow-cover than usual. The recent arctic vortex brought historic low temperatures over a weekend.
A common question was regarding the possible impact of the frigid temperatures of less than -40 Celsius, including wind chill factor, on plants and animals. Sadly, it seems the extreme cold will cause negative impacts with many Nova Scotia fruit crops such as grapes.
Many folks wonder if the tick population will be affected. Ticks are one of the toughest critters in North America. Ticks overwinter under layers of leaves and forest floor litter. They count on snow during the winter to protect them during cold spells. If there is no snow during cold spells, ticks are more at risk. As the thermometer decreases below -10 C, tick mortality increases, especially so for those unprotected by snow. During our recent arctic blast of cold, we had a small amount of snow, so there would not have been as much insulation protecting the bloodthirsty critters as is traditionally the case in mid-winter. Let’s hope the tick population decreases for the future.
INSECTS OF WINTER
One of the joys of winter is the absence of biting mosquitoes and black flies, stinging wasps, and gardening banes such as aphids. With the exception of a few insects, such as some dragonflies and butterflies, very few insects migrate to escape the cold. Insects survive the winter using one of two strategies: dormant or active overwintering.
DORMANT OVERWINTERING
Most insects wait out the winter by hiding out in a cozy little space under bark or in the soil until spring sunshine and longer days signal them to emerge. One way to do this is as an adult. A lot of beetles use this strategy. Whirligig beetles, for example, can be found in the warmer months, spinning dizzily on the surfaces of ponds as they swarm in groups in their search for food. As winter threatens, they climb onto the shore, burrow under the leaf litter, and wait for their pond to thaw again. Blow flies (commonly called ‘houseflies’) also lay low as adults; to our annoyance, they often do so in our homes, resulting in a buzz of activity on our windows on sunny, winter days.
Other insects overwinter as pupae, the intermediate stage preceding adulthood, or as larvae. Giant silkworm moths, such as the large luna moths, remain as pupae, bundled up in fist-sized cocoons in the woods. Some moths survive as larvae in the caterpillars stage. Most horse flies and deer flies live underwater during their larval stage.
Finally, some insects leave their eggs behind to tough out the weather. Many bugs lay eggs in the summer, and the eggs do not hatch until the following spring.
ACTIVE OVERWINTERING
A few insects do not avoid the cold weather but actually remain active while snow blankets the land. Many aquatic insects, such as predaceous diving beetles and dragonfly nymphs, search for other insects and crustaceans to eat while ice covers the pond or stream. They are fine as long as the ice does not freeze to the bottom.
Parasitic insects such as lice, never experience cold weather, since they are protected from the elements by the warm climate provided by the fur, down feathers, and hats of their hosts.
There are a few hardy insects in the Maritimes that can be found flying and crawling about during winter. Like fine-weather skiers, they are most likely to be out on warmer, sunny days as spring approaches. Snow fleas are amongst the smallest lovers of winter. They are springtails, not fleas, but true to their namesake, they do jump. In an around wooded areas, they appear as black specks jumping on the surface of the snow - especially in footprints - as they forage for the spores of fungi and lichen.
The chief advantage to being out and about during winter is that there are fewer predators around. Most insectivorous birds are not yet back. The amphibians are still snoozing. However, the insects are not totally safe. Shrews and moles are still foraging around and under the snow.