As winter closes in, someone just asked me whether a "killing frost" will kill the insects. That's a question just too large to answer! Yes, it will kill some of them, but there are many, many kinds of insects with as many different habits and cold tolerances.
A "killing frost" refers to plants, not animals. We see frost on the grass when temperatures fall to 32 F, which is the freezing point of water. Different temperatures kill different plants, and the temperature has to stay that cold for varying lengths of time. For example, 28 F kills corn down to the roots, but above that, will just damage leaves. Leaves of various perennial plants die at varying temperatures, but the roots do not. Basil leaves are damaged when temperatures go below 40 F.
Most insects can no longer move when the temperature is about 40 F, but that does not kill them. Killing temperature varies with insects and many have an antifreeze in their blood that allows them to survive severe cold.
Immature insects are most easily killed by cold, simply because they have to eat and grow, while adults don't grow and many don't even eat. Even if it is not cold enough to kill a plant-feeding insect, if its plant is killed by frost, it will quickly starve. If the insect is a carnivore and its prey dies, it will starve.
If you observe caterpillars, for example, you will see that they eat and grow while leaves are growing. By late summer and early fall, leaves have hardened and quit growing. The caterpillars usually pupate at that time, either on plants or in shelter. Larvae that get caught by cold weather are usually those that hatched late and were not ready for winter.
For that reason, very few insects are still in the larval stage when winter approaches. Some hibernate as full-grown larvae, and they take shelter in fall. Many reach the pupal or adult stage then, and some die as adults after laying eggs that hatch in spring.
Snow cover can be very good for insects. It provides an insulating blanket for those who live in the ground and those that hibernate under leaf litter, in soil and similar places. It keeps the ground temperature constant, and it protects them from predators.
Winter with little or no snow can be bad for insects, especially if there is a lot of temperature fluctuation. Ground that freezes and thaws heaves the soil. It can damage burrows and send insects in the soil closer to the surface, allowing birds and other predators to get to them easily.
Insects that hibernate as adults have stored up fat to allow them to sleep through winter, just like bears. Unseasonably warm temperatures awaken them, and they get active when food is not available. Activity uses up their fat reserves and they may starve before spring.
That is true of the much-hated stink bugs that get into homes for the winter, so most of them will be dead long before spring. However, since so many of them have found safe places to hibernate outdoors under constant cold, the death of the home invaders won't make a dent in the population!
Warm winters are bad for honey bees. They survive winters by staying in the hive, eating stored honey and fanning their wings to stay warm. However, if weather gets warm enough for them to go outside, they will fly around and look for flowers. This wastes energy and they will need to eat more. If they deplete their winter stores, the colony will starve.
Of course, all insects have ways of surviving normal winters, whether they are adults, larvae, pupae or eggs. It is unusual weather events that have the most effect on insects and all other life as well.
Send your insect questions to Claire Stuart by e-mail at firstname.lastname@example.org or write her (with self-addressed stamped envelope) in care of Living Section, The Journal, 207 W. King Street, Martinsburg, WV 25401.