As the season continues to cool, life outside is preparing for the cold. This includes the insects and spiders who must be able to survive exposure to freezing and sub-freezing temperatures. Insect development and survivorship is at the whim of the climate around them, in particular, temperature drives their lives. Some folks may be hoping that Old Man Winter will provide some free pest control in December or January. Unfortunately, insects have adapted many ways of mitigating the effects of cold and will be able to survive thanks to these “overwintering strategies.” When it comes to dealing with cold, there are two main ways for an insect to survive- either get away from the cold area completely or find local shelter that will provide some shielding.
Migration
Some insects may behave similarly to human “snowbirds” and simply leave when things start to get cold. Migration is a great way to not get cold, as a species you will simply go somewhere warmer! One of the most famous examples of this behavior is the monarch butterfly (Figure 1). In the autumn, these orange and black beauties will start to fly south from northern states, progressively moving towards Mexico. Once they arrive in Mexico, they fly towards the oyamel fir forests north of Mexico City where they will cluster together until spring. Another butterfly species, the painted lady, also migrates long distances and dragonflies are also noted for logging in a lot of frequent flier miles in response to cold.
Cold Tolerance
If they don’t pack up and go, then insects are still going to need to survive the winter to get populations restarted the next spring. For many species, this will mean finding an area that can protect them from cold air temperatures. It is important to point out that all species of insects have a lower lethal temperature, meaning there is a cold temperature that will kill them. Insects can’t warm their own bodies; their body temperature is dictated by their local climate. However, there is also a set amount of time that they must stay at that temperature for death to set in. If their temperature rises above that lower lethal temp, then the clock resets and they may survive. This gives scientists a freezing equation of temperature and time to know when bugs might die from cold.
Some insects may prepare for the cold and ultimately can survive being frozen. These species can produce natural anti-freezes that prevent them from freezing solid or lowering the normal lethal temperature. Other species may be able to control where ice crystals ultimately form in their body. They would let their fat bodies freeze for example rather than their digestive system.
If these freeze tolerance methods aren’t in their toolbox, an insect species is going to have to find a way to keep warm in a chilling environment. One trick bugs use is to go into winter as either eggs or pupae, stages of life that require much less food and are already semi protected. Mother bugs may lay their eggs in leaf litter, down in the soil, or provide extra protection. Bagworms and spotted lanternflies are good examples of moms that go the extra mile. Female bagworms never leave their bag-like construction, they lay their eggs inside with them and then perish (Figure 2). The bag then keeps those eggs slightly warmer than they would be outside. Spotted lanternfly females will “spray” a substance on top of their eggs, which helps the eggs to survive the winter.
Pupating insects often burrow into soil or leaf litter to finish the job. Once covered, they have a natural blanket between them and the cold air temps. Wood boring pests can also be highlighted as they are inside of a tree, under the bark and are rarely exposed to the frigid cold that may be hovering just outside their tree.
Some species may go into winter as adults. Brown marmorated stink bugs, multicolored Asian lady beetles, and boxelder bugs are some famous examples. Part of their fame is due to their penchant for using human buildings for their overwintering habitat. Instead of their usual hiding under logs or stones, they have found our homes to be deluxe, heated hideaways! This intersection of insect winter ecology and humanity can be quite annoying.
Pest-proofing Homes
If you have a history of dealing with winter infestations, your house most likely represents an ideal overwintering site to them. It may be down to the height of your home, its geographic situation, or even the color of the exterior. The best thing you can do for these issues is to pest proof the home as best as you can.
- Inspect your home and check for cracks around windows, doors, pipes, and chimneys and seal openings with silicone or silicone-latex caulk. You can consult another KPN article for more information on pest-proofing and using insecticides on the outside of the home.
- If you find insects congregating on the exterior of your home, you can spray them with soapy water to kill them before they get inside.
- When stinkbugs or lady beetles are discovered inside, simply vacuum up living specimens and dispose of them outside.
- Using bug bombs or other insecticides in the home will not help to deal with the lady beetles and will only serve to expose the people inside to residues. An exterior application of a perimeter insecticide may help to exclude some of these pests. This should be done with a pest control professional or by using a registered product (for example, Orthro Home Defense) and strictly following the label instructions.
By Jonathan L. Larson, Entomology Extension Specialist
Kentucky Pest News 