Where Do Insects Go in Winter?

Without a doubt, insect activity is greatly reduced during the winter months of November to February. Several environmental changes occur at the same time to cause this change in activity. The temperature begins to fall into ranges that stress the biology of insects, humidity in the air decreases and becomes dryer, and the hours of sunlight available each day has been reduced dramatically.

Insects don’t disappear entirely during the winter months, but their numbers have been greatly reduced. They are also less active and in many cases only certain stages of development are present. In cold unheated environments, insects will seek out protective places to over winter. Examples may include the use of cracks and crevices in walls or
floors adjacent to south and west walls, voids and spaces near ceilings or insulated areas; deeper penetration into stored food bins, bags or product, or possibly in protective leaf litter food spills, or under tree bark outdoors.

Each species of insects has a stage at which it is more tolerant to cold temperatures. Many species of stored food insects overwinter in a protective larval stage. These include Indianmeal moth, Mediterranean flour moth, Cigarette beetleDrugstore beetle, Warehouse beetle, Cadelle, Mealworms, Carpet beetles and Spider beetles. Some species, which have longer life spans as adults, overwinter as adults. These include Saw-toothed and Merchant grain beetles, Flat grain beetle, Flour beetles, Granary and Rice weevils, and Cadelle.  During these very cold temperatures there is virtually no activity and very slow metabolism.

Where buildings are less cold or there is some heat present, activity and reproduction can occur with very slow development rates such as with Saw-toothed grain beetles and Flour beetles. Despite such warmer conditions most stored food moths will remain in this period of inactivity (diapause) due to low humidity and short daylight hours. The Indianmeal moth for example will remain in diapause when there are less than 13.5 hours of daylight per day.

In Spring, when daylight hours begin to increase, humidity levels return to normal, and temperatures begin to rise above 60°F, adult insects begin to lay eggs; larvae complete development then go through a short pupation period to emerge as adults themselves.

Yes, the return of the “hordes” will be upon us soon.

By Alain VanRyckeghem


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