How do insects survive the winter? A lot of insects don’t survive the winter, and they haven’t evolved to. They are born, live long enough to reproduce, lay eggs, and die. However, that does not mean the species dies out. Many insects survive winter as eggs, larvae, nymphs, or pupae. Other insects live through the winter as adults by migrating to warmer places, finding somewhere sheltered, producing antifreeze-like chemicals, or entering a period of suspended development called diapause.
The easiest way to survive a cold winter is to move somewhere warmer, but the problem with that is the distance involved and the short lifetime of most insects. Monarch butterflies are famous for migrating thousands of kilometers, but their full yearly migration is spread over generations. The long-lived autumn generation flies south to overwinter, and later generations gradually move north again in the spring and summer. Other insects don’t really migrate in the same dramatic way. They simply move to a warmer microclimate nearby. They might crawl under bark, into soil, under fallen leaves, inside a shed, or sometimes into a house.
Some insects survive the winter by producing their own heat. Honeybees are a good example. A single honeybee would not last long in freezing weather, but a colony can survive by clustering together. The bees eat the honey they stored during summer and use that energy to generate body heat. They do this mainly by vibrating their flight muscles, not by flapping around the hive. The bees on the outside of the cluster act like insulation, while the bees in the middle stay warmer. If the colony runs out of food, it can freeze or starve before spring.
Some insects survive winter by producing their own antifreeze. This does not usually mean they can walk around normally in freezing weather. It means they can protect their cells from being destroyed by ice. The flightless Antarctic midge is an amazing example. It is the only insect native to Antarctica, and it spends most of its life as a larva. To survive the cold, the larvae lose a lot of the water from their bodies and produce protective sugars, such as trehalose. This matters because freezing water is dangerous inside cells. Ice crystals can tear membranes and damage the cell from the inside. By reducing the amount of free water and using sugars and other protective chemicals, the midge lowers the chance of deadly ice damage.
The Arctic woolly bear moth is another insect that can survive very low temperatures. The caterpillar can spend many years as a larva because the Arctic summer is so short. It eats for a few weeks, grows a little, and then shuts down again when the cold returns. To survive freezing, it produces cryoprotectants such as glycerol. Glycerol is a type of alcohol, and it helps stop water from freezing in the most damaging way. It is not exactly the same as putting a bottle of alcohol in the freezer, but the basic idea is similar. The chemistry changes how water freezes and helps protect the cells from ice damage.
A lot of insects survive winter in the egg phase, the pupal phase, or the larval phase. Many adult insects are not able to survive through the winter, but their eggs can. Eggs are small, protected, and often laid in places that are out of the worst weather. Some insects attach their eggs to the underside of leaves or branches. Others lay eggs in soil, bark, stems, or other sheltered places. When the weather warms up, the eggs hatch and the next generation begins.
A lot of insects also have a larval or nymph stage that can survive winter. Some caterpillars burrow into the soil or hide under leaf litter, where the temperature is steadier and the ground gives them some insulation. Dragonfly nymphs live in water, and they can survive under the surface. The top of a pond or lake may freeze in winter, but the water underneath usually stays liquid. The nymphs can stay there until spring. When the water warms up, they continue growing and eventually become adults.
Then there are insects that can pretty much switch themselves off. This is called diapause. It is a state of arrested development, and it is not only for winter. Insects can use diapause to survive cold, drought, lack of food, or other conditions that make normal life impossible. Different insects have different triggers. It could be temperature, food supply, moisture, or the amount of daylight. Whatever the trigger is, it changes the insect’s hormones. Growth, molting, and reproduction slow down or stop. Oxygen use drops, metabolism drops, and the insect waits.
Cicadas are a famous example, although they are not simply hibernating for 17 years. Periodical cicadas spend 13 or 17 years underground as nymphs, feeding on fluid from tree roots and growing very slowly. Their long life cycle is synchronized so that huge numbers emerge at the same time. When the soil warms to the right temperature, they come out, molt into adults, mate, lay eggs, and die. Their strategy is not just about surviving winter. It is about timing their lives so that most of them appear together.
Insects survive winter in many different ways. Some die and leave eggs behind. Some hide. Some migrate. Some make antifreeze. Some gather together and produce heat. Some shut their bodies down and wait. Winter looks like a dead time, but under bark, under leaves, under soil, under ice, and inside hives, insects are waiting for the world to warm up again. And this is what I learned today.
Sources
https://www.schlitzaudubon.org/2020/11/16/how-insects-survive-the-winter-diapause
https://en.wikipedia.org/wiki/Diapause
https://www.si.edu/spotlight/buginfo/winter
https://www.smithsonianmag.com/science-nature/what-do-insects-do-winter-180962183
Photo by Mustafa Mašetić: https://www.pexels.com/photo/serene-winter-landscape-in-lenningen-germany-30757600/