When Patty and her sister and brother go to the Eastern Shore on vacation, they like to take one of the boats from the dock and row out into the quiet inlet near their house. But they usually save their swimming for a pool.

The water near their house is part of the Chesapeake Bay. It's warm and salty, and for most of the time each summer it's full of jellyfish.

This year, there seems to be more of the clear, floating creatures with their dangling tentacles than ever. They're called "sea nettles." Like nettle plants that grow on land, sea nettles can deliver a nasty sting.

The sea nettle is just one kind of jellyfish. There are many other types in oceans around the world. Most jellyfish are shaped something like an umbrella, with tentacles attached like a fringe around the rim. Where the umbrella handle would be, there's a tube with a mouth on its tip.

A jellyfish uses the tentacles to capture its prey. The tentacles contain venom, or poison. The poison paralyzes the small sea creatures that jellyfish eat. Then the tentacles move the prey to the jellyfish's mouth.

The venom in most common types of jellyfish isn't powerful enough to cause big creatures -- like people -- much harm. But it can still sting. That's why Patty and her brother and sister prefer the pool to the bay during the sea nettle season in the Chesapeake Bay.

"The sea nettles start showing up about the last week of May or the first week of June each year. By the Fourth of July, much of the Chesapeake Bay is likely to have a jellyfish problem," says David Cargo, a research associate at the University of Maryland's Chesapeake Biological Laboratory on Solomon's Island in the bay.

Scientists conduct research on the complicated marine life in the bay at the lab. One of the things they study is sea nettles. "We have a big crop this year," Cargo adds. "Yesterday, I went down to the water to see. I counted at least 200 just in a small semicircle around the dock. We don't do too much swimming around here at this time of year."

The sea nettles, Cargo estimates, will stick around for another two to six weeks. Then they will be gone for another year. But they will have left their offspring behind to grow into next year's crop.

Right now, the sea nettles are busy spawning -- depositing immature forms of jellyfish that will live through the winter attached to rocks, piers and other hard things under the water. As the bay warms up late next spring, the spawn will grow into jellyfish, feed on plankton and other small sea animals, deposit more spawn -- and the cycle will start all over again.

When Patty went swimming earlier this summer, she didn't think she saw any jellyfish in the water. But when she came out of the water, she could feel some places on her leg that were tingling and stinging. She saw some little white bumps on her leg. Later, the area turned red.

"There must have been nettles in there after all," she thought. Patty's sea nettle sting didn't really hurt all that much, but it was annoying. Her mother helped her wash it off with a lot of fresh water. Then they put a paste made of baking soda on the red area. It soon felt better. Putting vinegar on the sting would have helped ease the pain, too.

So far, Patty has gotten through the rest of the summer without another sea nettle sting. She likes going to the pool, but she's looking forward to those warm weekends in September when she'll be able to sit on the dock and dangle her legs in the bay again. ::

Tips for Parents

A recent study in the Journal of the American Academy of Dermatology reports that the most common reaction to a jellyfish sting is a painful, itchy skin eruption. Small white bumps appear first, and then the area turns red. An individual's reaction depends on the amount of venom that the jellyfish releases, as well as the type of jellyfish involved. The rash may disappear within minutes, or it may linger for several hours.

However, severe jellyfish stings can cause dizziness, local cramping, fever and vomiting, and should be treated by a doctor. The Red Jelly, a variety that is present along the Atlantic Coast, delivers venom strong enough to cause painful welts. Muscle cramping may follow, so a swimmer who has been stung by a jellyfish should get out of the water promptly. Catherine O'Neill is a free-lance children's writer in Baltimore.