How do insects survive the winter?

Question

I had an interesting discussion today in which the question arose how insects survive in the winter. Since they need a high enough external temperature to be active, this seems a bit difficult in the winter. With frost they should completely freeze and I don't think they will survive this. Do they rely on eggs laid in the fall (which have to survive freezing temperatures as well) or do they employ other techniques for that?

Answer 1

The answer is nuanced. Most insects will die if you put them in a freezer for long enough (It is the method to euthanize research specimens). However, some insects have evolved various forms of cold-tolerance.

So first we need to take into account the geographical region (latitude and biome are an artifact of this) of which insects we are considering. E.g., insects in the tropics do not need to worry about overwintering and insects in the sub-tropics rarely have to subzero conditions. So, largely what we are considering is insects native to temperate regions. However, the adaptations of these insects pale in comparison to those which are native to boreal forests/tundra, some of which can live through being frozen solid.

Second, we should consider what actually happens to insects when they are subjected to cold and freezing temperatures. As you say, if insects are cold, their metabolisms slow down and they enter a period of dormancy called torpor. If they freeze entirely, do they die? It turns out, not always - it depends on the species of insect.

While your proposed strategy of laying eggs in the fall to last through the winter is one likely utilized by many species (e.g. mosquitoes), there are others. So, some examples:

Bees - social bees regulate heat by shivering for warmth, and creating hives that utilize air currents to regulate air temperature

Bumblebees, parasitic wasps - overwinter by burrowing underground (the temperature underground is

Wingless Midge - can survive being completely frozen. There are some caterpillars in the arctic, IIRC, that can as well.

Mosquitoes - eggs survive cold and freezing conditions (they are often some of the first flies to appear in spring)

Synanthropic insects - find a place to overwinter in a human dwelling.

Parasites - might survive winter by living inside an endothermic host

Hyper-parasites - might survive winter by living inside a parasite that is inside an endothermic host (and so on, and so on).

Other insects - either have anti-freezing chemicals in their blood.

And there are countless other strategies to be enumerated, but I think you get the idea.