Susan Blaul, age 12, of St. Paul, Minn., for her question:

What is the life span of the average fly?

The flies start life as eggs, then become maggots that turn into pupas. Most of the eggs, maggots and pupas end up as food for insects and other hungry little critters. The few that survive the first three life stages emerge as adult flies. Some of those that arrive in early spring may live three months or so. Those that arrive from late broods in the fall live only until the first frost. Some of the eggs and pupas survive the winter, but only a very few adult flies live until next spring.