Any discussion of insects over the winter is likely to elicit the term "overwintering." While its meaning can be as simple as indicating how an insect (or other animal or plant) spends its time over the winter, it more frequently is used to refer to a sort of hibernation undertaken by insects in order to survive the cold temperatures.
How Insects Overwinter
Insects can overwinter as:
- adults - When an insect overwinters as an adult, it is very similar to that of a bear hibernating in a cave.
Examples: ladybeetles, boxelder bug, stink bugs, cluster flies
- larvae - this "immature, wingless, feeding stage of an insect" will burrow deep into shelters, such as leaves, mulch or soil to keep itself warm. Some of these literally add an antifreeze (glycerol) to their system to enable
Examples: caterpillars, woodborers
- nymphs - the youth of the insect world are generally fairly inactive during overwintering, but some will live in ponds and streams beneath the surface ice.
Examples: dragonflies, crickets
- pupae - when an insect overwinters in this non-feeding, transitional stage, it will emerge from its harborage in the spring, as an adult.
Examples: moths, house flies
- eggs - some insects lay eggs in the fall for emergence in the spring.
Examples: mosquitoes, grasshoppers
Why Insects Overwinter
The purpose of overwintering is to create or find warmth in order to survive the cold. In overwintering, the insect goes into diapause, in which its development and growth is halted. The insect either has means of avoiding the cold or it undergoes physiological or biochemical changes to survive it, until a specific period passes or the insect begins to sense the lengthening days of spring.
Instead of surviving the winter winds in place, however, some insects head to more conducive lands through
migration - Some insects, such as the Monarch butterfly, cannot survive the harshness of winter, thus it makes its annual migration south to spend the winter in warmer temperatures, then return to its northern homeland when the weather eases in the spring.
Although most insect remain in their shelters until spring, insects that chose the shelter of a home's eaves, siding, cracks or crevices will often emerge into the warmth of the home at various times throughout the winter.
Such is the case of the cluster fly, which appears to be very similar to the house fly, and can cause great consternation and confusion for residents. While they may have adapted to seeing house flies during summer's heat, this slightly larger fly is not an expected winter pest.
The best way to control the indoor emergence of any overwintering pest is preventing its ability to harbor in the recesses of the building's structure through . During mid-summer, before the flies even begin to consider their potential overwintering spots:
- caulk or seal all openings near doors and windows; around pipes, outlets, and vents.
- caulk any splits in siding and cracks in foundations and walls.
- seal cracks or openings under eaves and along roofs.
- repair or replace any damaged screens.
It is particularly important to focus on the south side of the building, as the flies are attracted to these sun-warmed exterior walls, then, once landed, they begin to seek entry points for overwinter shelter. It can be helpful to have the south side of the structure treated with a pesticide in late summer, however because most effective pesticides are labeled as restricted use, the application should be made by a licensed professional, and all label directions carefully followed.
Even with this potential solution, however, prevention is best, as dead or decaying insects within walls can attract secondary insects, such as beetles and rodents.