Jan Mathis, age 13, of Sarasota, Fla., for her question:

HOW DOES A JELLYFISH STING?

The jellyfish are pretty creatures that look like helpless blobs of jelly. But don't trust them for a moment. They are armed with waspy stingers and the worst of them is more venomous than a poisonous snake. What's more, their stingers lash out from a distance, often inflicting painful red welts on human swimmers.

Jellyfish come in assorted sizes  from pea size midgets to giants that spread their jellified umbrellas seven feet wide. In our temperate seas their average size ranges from a few inches to more than a foot wide. The body of the average jellyfish is a hollow bag made from a thick layer of jelly sandwiched between two layers of cells.

The jellyfish is a meat eater who traps and stuns food and digests it in his hollow intestine. On his underside is a large mouth with maybe four loose hanging lips. Around the mouth are strings of dangling tentacles of assorted lengths.  They are armed with stingers.

The microscopic stinging cells are tiny round buttons called nematocysts. Each manufactures a long flexible thread bearing a poison that may be merely waspy or more deadly than a rattler's venom. The tentacles spread around to entrap passing victims. Merely a touch is enough to trigger numbers of nematocysts into action.

Then the tiny capsules burst open, exploding their long poisonous threads into the water. The explosive force pushes the poison into the victim's body. When paralyzed, the loose lips enfold the victim and stuff him into the mouth of the jellyfish.

A mindless jellyfish, of course, cannot distinguish between a manageable meal and a huge human swimmer. Hence the poisonous capsules explode when a person merely happens to brush against the tentacles. If the jellyfish happens to be a fairly mild type, the poisonous threads explode into the skin leaving long red lashes  maybe as painful as a swarm of angry hornets.

The most dangerous jellyfish is the sea wash, a squarish creature found in shallow seas off Japan, northern Australia and the  Philippines. His sting is deadly enough to kill a person in just a few minutes.

One of our nastiest jellyfish is the lovely blue Portuguese man of war, found along the shores of Florida. Actually he is a colony of creatures, sharing a single balloon that floats on the surface. After a storm, he may be washed on the beach. But beware, for his stinging cells remain active long after the critter is dead.