With the amount of snow we’ve gotten in the last couple weeks, you might find yourself wondering what happens to insects during the colder months of the year. As it turns out, the answer is not simply, “they die off.” Insects employ a number of strategies to combat freezing temperatures, so over the next few weeks we’ll take an in-depth look into the various ways insects deal with the cold.
One of the most well-known insect overwintering strategies is migration, made famous by the iconic monarch migration. Monarchs migrate from southern Canada to central Mexico and back again, over the course of 3 generations.
Therein lies the difference between insect migration and other animal migration: because of the relatively short lifespan of most insects, the adults that make it to overwintering sites are not the adults that return to their northern breeding sites.
The monarch migration is triggered by the onset of diapause, a state of dormancy and lowered metabolic rate that many insects enter during the colder winter months, though with the monarchs, they remain active (we’ll talk about diapause in a separate issue). The butterflies store excess lipids, proteins and carbohydrates to prepare for their migration south and subsequent migration northward once diapause has ended.
Monarchs may be the icon of insect migration, but they’re not the only insects that migrate south for the winter. The painted lady butterfly, which is found in temperate regions all over the globe, makes an annual southerly migration from Britain to the Mediterranean; The Worldwide Painted Lady Migration, a citizen science project based out of the Institute of Evolutionary Biology in Barcelona, has found that some populations can travel as far as Iceland to the Sahara.
Green Darner dragonflies are a North American species whose migratory patterns are not as well studied as the monarch, but who make a similar trek each winter from northern states to Texas and Mexico. They also happen to be the official insect of Washington, my home state.