In the summer, insects are everywhere: in your flower bed, buzzing around your head, squashed on the windshield of your car. Sometimes we appreciate them—buzzing bees that pollinate our flowers, beautiful butterflies, predatory insects like ladybugs that eat the nasty ones, etc.—, sometimes we loath them—the ones that eat our plants, bite us or try to climb into our ears. In all cases, though, they suddenly go missing in the fall, at least in temperate climates. Where do they go for the winter? And they certainly “go” somewhere, as when summer rolls in, they’re back.
Actually, insects and other arthropods have many different strategies for coping with the winter’s cold. Here are a few of them.
1. Long-Distance Travel
Some insects hightail it out of town before winter hits. The monarch butterfly (Danaus plexipplus) is the best-known example, largely because it migrates so visibly. But hundreds of other butterflies and moths migrate, notably the painted lady (Vanessa cardui), which travels up to 3 times farther than the monarch. Some grasshoppers and aphids migrate north and south, according to the seasons, as do many dragonflies. You could call these “snowbird insects,” as they mimic the migratory patterns of the “snowbirds”: Northerners who winter in Florida or Mexico and summer in coldest Canada or Alaska.
2. Just Succumb
Some insects migrate from mild climates to cold-winter ones in the summer, then simply die there when the cold hits: they don’t migrate back, at least not to any great degree. The corn earworm (moths of the genus Helicoverpa), also called the cotton bollworm and the tomato fruitworm, sometimes flies thousands of kilometers to summer fields in cold climates, annoying us by devastating our crops, but then simply dies when cold weather arrives. Not even the eggs it laid there survive. A new generation will arrive the following year, winging its way up from mild-winter areas again. Some aphids do the same. How this works as a survival strategy beats me, but that’s what they do!
3. Digging Down Deep
Some insects migrate … downwards. They move deeper into the soil than frost can reach overwinter there. Many aquatic insects spend the winter at the bottom of their pond, where the water doesn’t freeze. Often, they’re not dormant, but simply in a state of quiescence, living off their reserves and patiently waiting for spring before they eat again.
4. Turning to Humans for Help
Human structures, being heated from the inside, are warmer than the environment around them and some insects have learned to take advantage of this. They move into spaces under siding or cracks in wood and spend the winter there in the relative warmth they find. Often, they leave pheromone markings to tell future generations where to hide. The Asian ladybug (Harmonia axyridis) famously moves inside homes, forming aggregations of hundreds and causing no end of annoyance to home owners. Read When Ladybugs Invade for more information on that phenomenon.
5. Hardy Survivors
Some insects remain active in the winter, often wandering about under the snow or in dense grass. They often have a type of antifreeze in their system that allows them to tolerate extreme cold. Some species of springtails, often called snow fleas, while not technically insects, thrive in the far north, often on living on glaciers. Check out the snow in your yard this winter wearing your strongest reading glasses and you’ll likely see tiny dark spots moving blithely about at subzero temperatures. Bingo!
6. A Deep and Frozen Sleep
This is one of the most popular strategies. Such insects often crawl into some sort of shelter (often seedheads or fall leaves) and go into something close to dormancy: a state called diapause. Yes, they may have a sort of insect antifreeze called glycerol in their blood, but often we don’t know exactly how they do it. The arctic woolly bear caterpillar (Gynaephora groenlandica) has been known to survive temperatures as low as -70 ˚C, literally freezing solid. Such insects essentially stay frozen all winter, then wake up in the spring and carry on like nothing had happened. Some of these tough insects overwinter as adults, others as larvae or pupae.
7. Let the Next Generation Deal With It!
Of course, other insects lay eggs in the fall, occasionally out in the open, but most often in some sort of shelter (dead leaves, hollow plant stems, etc.). The adults then die, leaving the eggs to carry on and eggs can be very, very cold resistant. After all, don’t doctors successfully freeze human eggs, then implant them, producing perfectly healthy babies? Overwintering as an egg is a very popular strategy for winter survival.
Helping Beneficial Insects Through the Winter
Insects can be both helpful to humans, often feeding on insects that eat our crops, and harmful, eating those same crops … or us (mosquitoes, horseflies, etc.). To keep bad insect populations down, though, the best and most ecological strategy is to keep good insect populations up. And you can do a lot to help with that by protecting insect winter hiding places. These include:
Leaf Litter: Leave those fallen leaves where they lie, or least keep them on your property. You can add them as mulch to your flower beds, dump them in wooded areas, put them in the compost, but don’t throw them away or burn them, or you’ll be severely reducing the winter habitat of many beneficial insects.
Tall grass: Don’t mow your entire lawn short in the fall. Leave sections tall over winter to provide shelter for beneficial insects.
Stems and Seedheads: Many insects overwinter in seedheads or on or in plant stems. Help them survive the winter by not cleaning up your flower and vegetable beds in the fall. So simple!
Compost Piles: Whether your compost is neatly stored in a bin or just a big heap, lots of beneficial insects and other arthropods (beetles, spiders, centipedes, etc.) enjoy the warmth and protection they provide.
Soil: Many insects, including bumblebees, spend the winter underground. If possible, don’t disturb the soil in the fall, as that can let the cold sink to greater depths.
Dead Wood: Stumps, fallen trees, dead or hollow trees, they’re all great wintering places for a whole horde of insects. Plus many birds and mammals love a good dead or hollow tree as well. So if there is no serious reason for removing one, just let it stand… or lie, as the case may be.
Wood Piles: Very popular many insects, including some of the most beautiful butterflies, like the mourning cloak (Nymphalis antiopa).
Sheds and Structures: Insects often move into outbuildings to escape the chill. If there are a few gaps here and there, so much the better. Honeybees famously overwinter in human-made hives… or hollow trees.
Essentially, the more you leave your garden untouched in the fall, the healthier the beneficial insect population will be! So, when fall comes, just chill out, leaving your garden to fend for itself.