Greg PapkQ, age 7, of Buffalo Grove, I11., for his question:

HOW CAN A FLY WALK UPSIDE DOWN ON THE CEILING?

The fly seems to be defying gravity when he walks upside down on the ceiling.

The ends of the fly's feet are covered with tiny hairs, each with a disc at the tip. Some scientists say the discs act as suckers with a vacuum formed between the disc and the ceiling which holds up the fly by the pressure of the air. But if the fly is put into a jar and the air drawn out, the fly can still do his upside down walking act.

So other scientists say the magic is done by means of a sticky substance coming from the underside of the fly's foot. Each hair seems to be a tiny tube for holding the sticky liquid which is produced and poured out as required.