Eugene Davis, age 11, of Tucson, Ariz.for his question:

How can a fly walk upside down?

It is no trick for a fly to walk upside down on the ceiling. He may even pause there to brush off his furry coat, balancing on only four of his six legs. It is the amazing feet on these six legs which enable him to do this upside down acrobatic stunt.

Each leg is encased in a hard, leathery shell which bristles with hairs. Under a microscope, these hairs look like miniature spikes and the foot itself is strange beyond belief. The main part of the foot is a pair of prongs, curved like the horns of a Jersey cow. At the base of each prong is a small round pad covered with tiny hairs.

The fly can use the prongs on each foot like a pair of tongs. As he walks over a rough surface, the prongs hook around little bumps and cling, The pads under the prongs give off a slightly sticky fluid. This goo is not strong enough to cement the foot to a wall or ceiling, It merely prevents the fly from slipping and falling should the prongs lone their grip. With the prongs and pads working together, the fly is able to walk with ease, clamping down one foot and pulling up another.

These strange feet work well for the fly because he is such a small animal. He is only one quarter inch long with a gauzy wingspread of half an inch. He weighs less than one thousandth part of an ounce. To him, a thimble is as big as a room, a falling leaf big as a plane.

To us, the ceiling may look very smooth and flat. But the little fly sees it as a wide expanse of boulders and pits. He uses the pincers on his six strange feet to grab hold of these irregularities,

This upside down trick is fascinating to watch and under the microscope the fly is a fuzzy, interesting looking little animal. However, when it comes to our daily lives, he is far from attractive. He is by nature a scavenger, very fond of soft bits of garbage of all kinds.

And tiny microscopic bacteria thrive in piles of garbage.  Some, but not all of these bacteria are dangerous, very dangerous to us. We call these microscopic enemies of ours pathogens and pathogens abound in decaying garbage.

Mr. Fly inspects any open garbage can. Small as he is, the bacteria are small enough for a million of them to stick to his hairy body. Then off he zooms, maybe through a kitchen window. Wherever he lands, scores of the pathogens may stay behind  an idea which is very unpleasant to think about. So we do something about it.

Sensible people keep lids on garbage cans, screens on doors and windows. The community often takes a hand to protect itself from these disease carrying house flies. Places where flies breed should be found and sprayed with insecticides. And, of course, everyone should swat a housefly at every opportunity.