Have you ever wondered just where those hordes of mosquitoes disappear to come winter? Just how do they manage to make it through the long periods of below freezing temperatures so prevalent in the Rockies? Like all of the residents of the mountain environs insects have developed a number of unique strategies for dealing with winter.
Unlike mammals and birds, insects don't have any way to regulate their body temperature. They are basically a liquid filled box without the intricate systems of veins and arteries found in higher animals. Since the six legged version of blood contains a large amount of water, it doesn't take very cold temperatures to leave them frozen solid. Generally they've developed five different strategies for overwintering: migration, dormancy, communal living, staying active and hardening.
When we mention migration we tend to focus on the huge flocks of geese heading to warmer climes for the winter. In fact, monarch butterflies follow a similar migration and travel thousands of miles--all the way to Mexico. Generally though, the migrations are vertical. Many migrate far down into the ground to get below the frost level and avoid freezing. In Rat's Nest Cave, on Grotto Mountain, I've seen huge accumulations of Daddy-Long-Legs well below the freezing point. Although not insects, they are equally as susceptible to the cold temperatures and so collect in fist-sized balls of hundreds of individuals.
Like ground squirrels, many spend the winter in various forms of dormancy. Generally, though the dormant months are spent in stages other than adulthood. Often they will overwinter as eggs, larvae or pupae (cocoons). A lot of aquatic insects will burrow into the mud.Ants and bees, living in huge colonies, are able to change the conditions found within their colonies. For instance, the rapid activity found in most beehives is sufficient to raise the temperature of the hive above the freezing point.
Some animals just seem to defy the winter cold by staying active despite the weather. On warm winter days you can see snow fleas and springtails moving around on the surface of the snow. Those animals living under water often remain active as if it were the middle of summer. Anyone who has jumped into a mountain stream in July knows that they don't tend to get very warm anyway. Caddisflies mate in February and some small black flies will even emerge to crawl around on the snow.
Perhaps the most amazing adaptations are known as cold-hardening. Some insects can "supercool" themselves to protect them in temperatures as low as -35° C and in rare cases -60° C. Very small droplets of water tend to freeze at temperatures much lower than freezing. Very small droplets of water sometimes remain liquid to temperatures as low as -31°C. By isolating their bodily fluids into small droplets insects are able to supercool without freezing--as long as they remain motionless. Even the slightest movement would cause flash freezing and death. In addition to hardening, some insects seem to produce "cryoprotectants" or chemicals to prevent freezing.
Winter is tough enough on those animals able to regulate their body temperatures. Insects have had to develop more unique survival strategies to ensure their continued reappearance every spring.