Every autumn I begin to wonder: where do all the bugs go? Unlike people, and other warm-blooded critters that can maintain a consistent internal temperature, insects cannot. So, you might wonder, what do insects do to survive the cold?
Insects have many strategies for surviving winter. Some of these are unique to insects, and some are shared with other animals. For instance, some insects, like ladybugs, do something similar to bears: they hibernate. The adult insects find a warm spot to spend the winter, and frequently huddle in large groups to help conserve heat. During this time, ladybugs become less active and their need for food decreases dramatically.
Alternatively, because insects have several life stages, some of which are more active than others, some species just extend a relatively inactive stage. For example, some beetles spend the winter as pupae, the stage between a larva and an adult. When a beetle hatches from an egg, it is a larva, or grub-like form. Because larvae are pretty much eating machines, they store up plenty of food early to make it through the pupal stage without eating. Pupae only need to breathe, which allows them to remain in one spot and save energy. Beetle pupae often spend the winter protected from the harsh elements far underground or inside tree trunks.
Then again, some insects leave town altogether. For example, monarch butterflies travel up to three-thousand miles to find a warm spot to spend the winter. Monarchs west of the Rockies fly to the coast of California, while monarchs east of the divide travel to the mountains of Mexico, where millions hundreds of them cluster in trees at high elevations. These groups, called roosts, form an amazing sea of orange that truly is was one of the world's natural wonders. However, insects don't need to fly across the continent to be considered migratory. Some insects living high in the mountains, such as some flower-feeding beetles, simply fly to a lower elevation where it's warmer. But even this can be considered a long road trip for a tiny insect.
While some insects exhibit behavioral techniques to survive the winter, others undergo internal changes. Some insects don't fight the temperatures; rather, they allow their bodies to freeze and become living popsicles. They do this by producing chemicals that encourage freezing of the liquid in areas between the cells of their bodies, but not within the cells themselves. If the cells themselves froze, they would expand and rupture and the insect would die. Instead, freezing of the liquid around cells pulls liquid out of them, drying them so they can't freeze. However, this method takes time; a rapid drop in temperature will kill the insect.
Other insects, like the snow fleas you might see later this winter hopping about in shadows on sunny days, prevent any liquid inside their bodies from freezing. They do so by making their own form of antifreeze. Just as in a car radiator, certain chemicals lower the freezing point of a liquid inside insect's bodies, preventing it from freezing. Studies of these chemicals may someday allow us to better store organs for human transplantation, or even make better ice cream. But these chemicals can have a downside for insects. Insects don't make them year round because these chemicals can be deadly at warm temperatures. That's why, when you see insects on a sunny winter day, they're typically hanging out in the shadows. If they spend too much time in the sun, they’ll get too warm and die, poisoned by the same chemicals they made in order to survive the cold. So, if you spot insects hopping about on the snow this winter, try to avoid the temptation to pick them up. The heat from your hand could be too hot for them to handle.
"Field Notes" is produced by the Montana Natural History Center.