Karen St. Onge, age 10, of Lethbridge, Alta., Canada, for her question:
WHERE DO FLIES SPEND THE WINTER?
There are about 100,000 different flies in the world, but the one we know best is the pesky housefly. Through the summer we see swarms of houseflies, especially around piles of trash and lidless garbage cans. But when the cold weather arrives, all of them disappear. It's no use to hope that they will never return, for come spring there are more swarms of flies.
We know that flocks of birds disappear before the first frost because they fly south to spend the winter. Swarms of flies also disappear in the fall. But the tiny critters certainly cannot fly hundreds of miles to a warmer climate. Actually they do not even try to migrate.
The houseflies and other flies are insects. And all the insects have their own strange ways to get through the changing seasons. The pesky housefly lives through four different stages. We notice her only in the final stage when she is an adult and has wings to fly around. During the summer she lays perhaps 1,000 eggs.
Most likely the busy little mother pokes her tiny white eggs down into a pile of garbage or some other decaying material. She may lay 250 eggs at a time and another batch in a few days. If the weather is warm, this morning's eggs will hatch this evening or tomorrow morning. Now they are wriggly little maggots.
These grubby creatures are interested in eating, and nothing else. They feast on decaying material, which is why their mother put them in a pile of garbage. As they eat, they grow too big for their skins. So several times they shed their old skins for larger ones. At last the grubby maggots are ready for their pupa stage of life.
The pupas seem to be sleeping in their tight fitting skins. Actually the insects inside are going through a miraculous change. When their skins crack open, they come forth as adult insects with wings. These are the houseflies that pester our summer days. As a rule, they live only about a month. And all of them perish before the first frost which is why we do not see them around during the winter.
However, the next generation is in hiding, just waiting for the first day of spring. Some are in the egg stage and some in the pupa stage.
During the summer season, the winged grown up flies produce brood after brood of eggs. But none of the adults lives through the winter. However, when the warm weather returns, the sleeping eggs hatch into hungry maggots. The pupas hatch into winged adults, all ready to produce another generation of housefly eggs.