Jonathan Serf, age 16, of Muncie, Indiana, for his question:

Do flies hibernate?

Insects of the house fly type are germ carrying pests and reducing their populations is a matter of public health. In winter, their aggravating squadrons disappear from the scene and we tend to forget about them. Or we may relax and think that somehow the problem has solved itself. These lazy daydreams are dashed with the first warm breath of spring, when swarms of flies reappear from who knows where. Actually they were with us all the time, though not hibernating like the bears and beavers.

When chemical .insecticides were recognized as dangerous pollutants, we had to seek safer methods to wipe out flies and other insect pests. The sensible approach is to learn the weak, vulnerable spots in their life cycles. However, insects are very secretive about the most vulnerable phases of their lives. We notice them only when they take to the air as winged adults. This is the breeding season, when a few adults can hide enough eggs to populate the world with another generation.

The life cycle of the house fly develops through four very different stages, three of which are capable of surviving the winter. All houseflies look alike but those that appear in spring are not the same individuals that disappeared in the fall. Some of the new arrivals spent the whole winter as eggs. Others hatched and spent part of the time as maggoty larvae or sleeping pupae. We failed to notice them because they were cunningly concealed. When we know the likely hideaways, we can destroy them before next season's reproductive cycles begin.

During the summer, a female house fly produces thousands of offspring every month or so. Each brood completes the egg, larva and pupa stage in about two weeks and hatches into mature winged insects, ready to start new generations. In late fall, a female conceals a final brood of eggs    and perishes. The tiny eggs may be tucked away into a suitable crevice indoors, or more likely somewhere on the premises outdoors.

Favorite indoor hideaways include the corners and crevices inside the kitchen cabinet that houses the trash can. When the maggots hatch they usually can count on enough tiny food scraps and the larvae can sleep undisturbed in the warm darkness. Favorite places outdoors include piles of steamy manure and neglected crevices in and around garbage cans. The eggs, larvae and pupae of various pesky flies often winter in these same places. So we may attack several species in the same operation.

The basic method is a spic and span sanitation operation. Indoors, one of our safest weapons against the future flies is soap and water. The attack calls for the sort of scrubbing that roots out every speck of possible maggot food    until every impossible corner is cleaner than clean. The best weapon outdoors is a compost pile, in which the future flies are destroyed by the heat of decomposition