Posted by: Jessica Wong, PhD Student, CSU Department of Bioagricultural Sciences and Pest Management
Insects have remarkable strategies for surviving Colorado winters. A few species migrate to escape the cold. The most well-known species to do this is of course the monarch butterfly. By now they have made their way to roosting sites in Mexico (or California in the case of monarchs from the Western Slope). The green darner, Colorado’s largest dragonfly, is another species that makes its way south before winter arrives. For the rest of the insects that can’t fly thousands of miles, they stay put right here in Colorado.
Most insects have figured out how to survive our cold, dry, snowy, sometimes balmy winters. A few, like brown marmorated stink bugs and multicolored Asian lady beetles, will escape the cold by going indoors. Cracks and gaps in door and window frames are great opportunities for them, so make sure those are well sealed to prevent them from invading your house. The rest of the insects stay outdoors and go dormant. These insects produce their own antifreeze compounds to withstand temperatures well below 32 degrees. And they have genetic programming that prevent them from coming out of dormancy too early, which is handy on that 70 degree day in February.  |
| Multicolored Asian lady beetles preparing to overwinter. Photo by Howard Russell & Christine DiFonzo, Michigan State University |
Insects overwinter in different life stages – egg, larva, pupa, or adult – depending on species. Most species of aphids and crickets survive the winter as eggs. Aphid eggs can be found on trees and shrubs, and cricket eggs can be found in the soil. Japanese beetle and emerald ash borer are two serious pests that overwinter as larvae (also known as grubs). Japanese beetle grubs spend the winter in the soil under turfgrass, such as your lawn. Emerald ash borers overwinter in their galleries just under the bark of ash trees.  |
Japanese beetle larvae. Photo by David Shetlar, the Ohio State University |
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| Emerald ash borer larva in its gallery. Photo by Howard Russell, Michigan state University |
Black swallowtail butterflies survive the winter in their pupal (chrysalis) form, while another butterfly species, the mourning cloak, overwinters as adults. Bumblebees and yellowjackets also overwinter in the adult stage. Both bumblebees and yellowjackets are social insects with colonies in the spring and summer, but in the fall workers start to die and only fertilized queens survive through the winter. When spring finally comes all the insects break dormancy and resume their unique life cycles.  |
| Black swallowtail pupa. Photo by Donald Hall, University of Florida |
