Tom Turpin
Professor of
Purdue University







Where Do Bugs Come From?

Some insects always seem to appear mysteriously. For instance, fruit flies invariably show up around ripe fruit left sitting for a day or two on a kitchen counter. Weevils have been known to appear overnight in flour or in a box of breakfast cereal. The unexpected presence of insects prompts many homeowners to ask, "Where did they come from?"

It's an old question. Insects, it seems, have been appearing from out of nowhere for ages. In fact, insects were probably the creatures responsible for the theory of spontaneous generation. This disproven concept, that life forms could be generated from any number of inanimate substances, might have arisen to explain the sudden presence of insects.

Insects, unlike larger animals where the birth process is easily observed, and unlike microorganisms that can't be seen at all with the unaided eye, are large enough to see but not large enough to see well. Even harder to see than the insect itself are the eggs or newly hatched immatures. Consequently, the adults are frequently the first readily visible insect stage. Many adult insects even flaunt their presence by flying around, a guarantee that we humans will see them.

Francesco Redi was the scientist who disproved the theory of spontaneous generation. In his test, where he proved that "if living causes be excluded, no living things arise," he used insects — flies to be exact. Redi, a poet, antiquary, physician and naturalist from Florence, wrote in 1668 that he "began to believe that all worms found in meat were derived from flies, and not from putrefaction. "I was confirmed by observing that, before the meat became wormy, there hovered over it flies of that very kind that later bred in it."

Redi confirmed his observations by an experiment that used what today we call controls. He placed in open flasks a dead snake, some dead fish and a slice of veal. For comparison, he duplicated the experiment with one modification — he covered the flasks with gauze. In the open flasks Redi found maggots, although none could be found in the closed flasks. He correctly concluded, "The flesh of dead animals cannot engender worms unless the eggs of the living be deposited therein."

Even though it seems at times that insects just appear from nowhere, what Redi discovered over 300 years ago is still true today. So when we find insects emerging from food in our pantry it means one of two things: Either the food contained insect eggs when we procured it, or adult insects were able to find the food and lay eggs in it. In neither instance did the insects appear from nowhere — it just seems that way!


Writer: Tom Turpin
Editor: Andrea McCann