While we may have complained about an early cold snap this year, we certainly did not complain when the mosquitoes disappeared. But where are they now? Did the frost kill them all? And how do they reappear with the first couple warm days in the spring?
There are several dozen species of mosquitoes found in Alaska, and each of them has its own particular life cycle, although all of them are aquatic. Some prefer lakes, others ponds or various marshy habitats. Eggs are laid in the water and hatch out to become “wrigglers,” or larvae. Most of the larvae feed on algae or dead plant materials. They then form a pupa and shortly afterward emerge and become the aerial mosquitoes we love to hate.
The females usually mate and then look for a blood meal — and your arm looks like a great source of that blood. Note that only the females need a blood meal, so those buzzing around your head are all female mosquitoes.
When you and I swat at the mosquito that’s buzzing about, we probably don’t take the time to differentiate the particular species. But each species has its own approach to surviving the Alaska winters.
Many species overwinter as an egg that is laid in water during late summer or early fall. The egg remains underwater in a diapause state of inactivity until spring thaws. In the spring when water temperatures rise, the eggs hatch and the larvae feed voraciously. Within a week or so, they pupate and quickly become the aerial insects we know so well.
Another overwintering approach is for adults to find a safe hiding spot and wait out the cold of winter. Often these hiding spots are within leaf piles on the forest floor, in tree holes or under tree stumps. These areas, especially with a snow cover, provide insulation from the very coldest temperatures of winter.
An important goal for overwintering adults is to prevent ice crystal formation within their hemolymph (insect blood). First they reduce the amount of water in their hemolymph, kind of like concentrating their blood. Then they produce glycerol within the hemolymph, which acts as antifreeze. Now the adult is protected down to some pretty impressive temperatures. This activity is just like what we do to our automobile radiators each winter. However, if the temperatures around the adult fall below their protected temperature range, the adult will die. Very cold temperatures during a winter with minimal snow cover can reduce the spring population of early mosquitoes.
For overwintering adults, when the ambient temperatures rise in the spring, they are quickly able to leave the hiding place and seek out a blood meal. One particularly large Alaska mosquito uses this overwintering technique so well that it is called the “snow mosquito.” These are usually the first large mosquitoes we see flying around when there is still snow on the ground in early April.
While people are enjoying wintertime activities like skiing, snowmachining or ice fishing, beneath the snow and ice are mosquito adults or eggs, waiting for the return of warmer temperatures.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the biology of the Kenai River watershed.