After Missouri experienced some bitter cold temperatures during the first 10 days of the new year, I received questions regarding the effects of the low temperatures on this year’s populations of ticks, chiggers, armadillos and insects. I’m sure many people are hoping to see fewer outdoor pests this year. This winter’s below-zero temperatures occurred when there were several inches of snow on the ground in much of the state. That layer of snow with trapped air acts as an insulating blanket, keeping leaf litter and the soil below protected from dramatic low temperatures. We may have been more likely to see the effects of below-zero readings if the ground had been snow-free at the time.
Many factors determine insect populations in a given year, making abundance in a particular year difficult to predict. Low temperatures during the previous winter may affect some groups. Most insects, however, are well-adapted to the cold temperatures and have mechanisms for dealing with cold weather. Some overwinter in the living tissues of plants, in leaf litter or underground where they are insulated from extreme temperatures. Others go into a state of hibernation, called diapause, during which they are more tolerant of cold weather. Dramatic fluctuations in winter temperatures may have a greater effect than extreme lows, if insects are “tricked” into becoming active and then cold temperatures return.
On the other hand, there are northern range limits for most North American species, and those limits are often determined by extreme winter conditions. The armadillo is a species that seems to be defying our previous thinking on its northern range limit as each year finds them in more northern areas. A cold winter may slow that northward movement as unprotected animals that have reached the most northern zones may be killed by the cold. However, if only a few individuals are able to find warmer places to survive, they will soon be reproducing and rebuilding their population.
Chiggers overwinter in the soil and some species occur as far north as southern Canada, so there are chiggers that are well able to withstand the cold that we experience in the worst Missouri winter. Ticks can be found in various habitats throughout the world, so at least some species are extremely cold-tolerant. It would be difficult to predict whether you will see fewer outdoor pests this summer. In my experience, the number of ticks and chiggers you encounter depends on where you go, regardless of the previous winter weather. In the same summer, one place will be thick with pests and other places may be free of them. I wouldn’t count on a dramatic reduction due to our recent low temperatures.