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Sunlight & Seasons

Frozen Insects
How Insects Survive Cold Winters

When the temperature is below freezing, insects and other cold-blooded animals cannot be active. Some, like monarchs, migrate to escape the cold temperatures. But even in the dead of winter in the far north, many insects are still alive. Some are even very active! How can that be? In this lesson we'll see how insects survive cold winters, depending on where in their life cycle they are. Then we'll do some journaling, imagining what it's like for insects to live through winter.

Where Are the Insects?
The easiest winters for insects are the ones when the temperature gradually gets cold, stays cold, and then gradually gets warm as spring arrives. But even in the worst winters, a LOT of insects survive. Where are they? Many are hiding and even eating a little bit in micro-habitats that aren’t as cold as the open air. They can be in such places as:

the soil
under logs, rocks, and fallen leaves
inside the wood of logs and trees
inside special bumps on plants called galls
near windowsills, eaves, and attics of houses

Insects do not hibernate. Hibernation is usually considered to be something only warm-blooded animals do, when they allow their body temperature to drop very close to freezing. Insects are cold-blooded, so it’s not a change for their body temperature to be close to air temperature. When insect eggs, larvae, pupae, or adults are inactive during the winter months, with their growth, development, and activities suspended temporarily, we call the dormant condition diapause. Even though they stay alive, insects in diapause hardly move at all. Insects that are somewhat active in winter are very, very sluggish.

Life Cycle Makes a Difference!
Different insects survive winter in all four stages of life.

Adults
Many insects, such as ladybugs, survive winter as adults, sometimes alone, and sometimes in large groups. Ladybugs often gather in huge masses on and near beaches for the winter. In fall and spring, before and after they've survived the winter together, they're often seen in great numbers.

Many wasps and fly adults move into the eaves and attics of houses or barns. Many other adult insect species hide in tree cavities, under leaf litter, or under logs and rocks. The Mourning Cloak Butterfly is usually the first butterfly we see in spring because it spends the winter as an adult in tree holes or other shelters, ready to emerge as soon as the temperature rises above freezing.

Honey bees stay in their hives during the winter, and form clusters when temperatures fall. They can raise the temperature by vibrating wing muscles. A hive can use up 30 pounds of stored honey during the winter. Just digesting and using the honey to stay alive produces heat, and the action of vibrating the wing muscles both produces heat and circulates it throughout the hive.

Many adult insects reduce the water in their bodies and produce glycerol, a chemical that acts as an antifreeze.
Eggs
Some insects overwinter as eggs. The mother insect usually lays these eggs in protected areas. The praying mantis is one example. Eggs are fragile and many freeze too easily to survive winter, so a great many kinds of insects wait until spring or summer to lay eggs.
Larvae and Nymphs
Some insects overwinter as larvae. Many of these are protected by leaf litter or burrow deep into the ground. Some, like wood-boring beetles, chew their way deep into tree wood. When insects lay their eggs in some kinds of plants, the plants have an allergic reaction, and grow a large, thick bump around the egg. This thick bump is called a gall, and it actually protects the larva that hatches out. One kind of fly larvae that spends the winter in galls is popular with fishermen who use it as bait in winter. Like adults, many larvae produce glycerol to protect their tissues from freezing.

Some insects don’t spend any part of their lives as larvae. Instead, when they hatch from eggs underwater they go through the next life stage as nymphs. Nymphs can move around more quickly and easily than most larvae and have more complex bodies than most larvae. Some remain in this stage of life for two or even three years. Dragonflies, mayflies, stoneflies, mosquitoes, and some other flying insects spend the first part of their lives in rivers, streams, lakes, and ponds. Ice may cover the surface, but in the water beneath the ice, these insects can actually be very active, feeding and growing.
Pupae
Some insects, such as certain moths, overwinter as pupae, then emerge in the spring as adults. Some of these pupae may produce glycerol, too, to protect their tissues from freezing.

TryThis! Journaling Question

Imagine you’re in a big swimming pool filled with thick molasses up to your neck. You have to work very hard to get anywhere, and your movements are very slow. Do you think this is what it feels like to be an insect or other cold-blooded animal in winter? Why would food be harder for an insect to eat in winter than summer? How might breathing be more difficult in freezing weather?