How Insects Survive the Winter Months
Written By: Patrick Kelley, BCE
It is harvest-time and the use of cinnamon and pumpkin spices in seasonal foods shoots sky high. While the leaves on the trees have mostly turned their fall colors and fallen to the ground, there is a chill in the air that hasn’t been felt since early spring. Some cloudy and/or rainy days followed by sunshine and near freezing temperatures at night begin to become commonplace. This is typically how autumn feels in temperate climates.
While the temperatures drop, insects busy themselves with preparing for the dead-cold of winter. The survival strategies of insects differ depending on the species. Here are a few of the ways that our six-legged friends prepare for winter and live to see the next spring.
In autumn, a monarch butterfly emerges from its chrysalis in preparation for a long journey to warmer climates to avoid the freezing temperatures of winter. Photo: purchased use rights from Shutterstock
Flight, not Fight
One of the best ways to avoid freezing to death is to avoid the freezing temperatures altogether. Insect migration from cold to warm climates allows the insects to live in warmer temperatures after a potentially long trip from the colder climates. Monarch Butterflies are a well-known example of insect migration as populations begin to move in great numbers around mid-August to head south toward warmer climates.
The decreasing length of days, the plunging temperatures and the aging milkweed sources in the colder temperatures trigger the birth of a super-generation of butterflies that live up to eight times as long as their previous two generations. Their long life along with large fat stores packed away by the larval stage allows this generation to travel as far as 3,000 miles (4,800 km).
Go Ahead and Freeze Me…. I Dare You
While it is possible to kill insects with extreme cold, this only works if they are dropped from relatively warm temperatures ( >70° F/21° C) to freezing temperature (<10° F /-12° F) over the matter of several hours. This is called “thermal shock”. Most insects that live in temperate climates find a way to avoid thermal shock and survive winters. All the insects we know today that live in temperate climates have survived for hundreds of generations through some of the world’s coldest winters, so we know that they are good at this job.
Egg Survival in the Winter
Only a few insect species overwinter as eggs. Corn rootworm beetles will bury their eggs deep in the soil adjacent to the plants that they will attack and feed on when they hatch. Praying mantids lay a foamy and insulated egg mass on pine trees that will emerge in the spring (or even when Christmas trees are brought indoors into warmer conditions in December).
Larval Survival in the Winter
There are several ways besides migration that insects escape a death by freezing. Many insect species will overwinter in the larval stage. As the temperatures start to drop in the fall season, the larvae prepare themselves for freezing temps by evacuating all the water molecules in their bodies and replacing that water with glycerol. Glycerol can be considered a type of antifreeze. This exercise prevents any water molecules from expanding and damaging the insect’s internal organs after being frozen. Glycerol acts the same way that antifreeze works in our cars. Once this swap of fluids is complete, the insects can be completely frozen and can safely remain in diapause (a state of suspended animation) until spring thaws occur. Other larvae, such as woolly bear caterpillars protect themselves from cold by growing a heavy outer covering of hair around their bodies like a heavy winter coat. Other larvae will bury themselves in leaf-litter as a barrier to the cold and some will even burrow deep down into the soil to prevent themselves from being frozen.
As fall temperatures cool, insects prepare for freezing temperatures by expelling water molecules from their bodies that would expand and eventually kill them when the temps drop below freezing. They replace the water with glycerol that acts the same way that antifreeze works in our cars. Once this is complete, they can be completely frozen and safely remain in diapause (a state of suspended animation) until a spring thaw occurs.
Nymphal Survival in the Winter
Insects can also overwing in other life stages besides larvae and eggs. Aquatic insects like dragonflies, stoneflies and mayflies go through a nymphal stage that remain active while being completely submerged in ponds, streams or rivers throughout the winter months. Often living under ice, these nymphs will feed throughout the winter and finally emerge as adults in the spring.
Pupal Survival in the Winter
Some of the larger and more impressive moth species in the family Saturniidae live throughout the winter attached as pupae in a cocoon on a tree branch or other plant branch that they feed on as caterpillars.
Honeybees generate their own body heat along with the heat produced by the oxidation of the honey. The adult bees will then rapidly beat their wings to distribute the heat throughout the hive.
Adult Survival in the Winter
Adults can survive through a cold winter if they find protected harborage such as a hollow tree or in bulging plant galls. One unique insect that lives throughout the winter as an adult is the honeybee. The oxidation of the honey that bees produce and feed on in the winter allows them to generate body heat. The heat is then dispersed throughout the colony by the bees rapidly beating their wings to create a fan-like effect. This is a truly unique way to heat your abode!
All in all, insects are amazingly resilient. They find ways to survive cold winters by becoming mobile transients or immobile zombies that are barely alive. They find ways to survive by digging in deep or by surrounding themselves with blanketed thermal layers that they themselves produce. Some even can generate their own heat. Insects have survived this way since the beginning of time and will continue to amaze us with their methods of perpetuating the next generation even when the odds are against them.
Reference
Smithsonian Institution, BugInfo Spotlight, Where Do Insects Go in the Winter, Website: https:// www.si.edu/spotlight/buginfo/winter visited in October 2024
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