If you've been stung by sea nettles while trying to swim in the summer Chesapeake, you would expect these irritating creatures to be a prominent feature in the Bay's historical record, but they're not.

These unpopular jellyfish probably take their name from the European "stinging nettle," a leggy, briar-like plant with tiny silica spines on the stems that break off beneath the skin and release an irritating fluid.

English colonists knew this plant well but weren't fussy about how they applied the name - in the late 1600s, one reference to a "sea nettle" being brought up in a bucket off the Virginia capes turned out, upon inspection, to have been a Portuguese man-o-war (Physalia physalis).

The broad Colonial literature is silent until 1750, when the Maryland Gazette reports that James Mitchell, an Annapolis man, "met with a singular and fatal accident" when he "became entangled in a great number of sea-nettles and was drowned." The Barrie brothers, yachtsmen who cruised Chesapeake Bay in 1899, reported nettles interfering with their swimming south of Annapolis. From the 1920s to the 1940s, there are sporadic complaints recorded from commercial fisherman about stinging nettles being"hot" as they hauled their seine nets, or being bad enough for nets to be taken in altogether. Screens to keep out the the nettles were common around swimming beaches in the '30s and '40s.

I've worked in the Chesapeake for 28 years, and for most of that time there was a news item each year as we headed toward summer: "Maryland scientist gives sea nettle forecast." For decades, these articles always quoted Dave Cargo, of the Chesapeake Biological Laboratory. He's a tall, strong, bespectacled man with thinning hair. There's a wide smile but a crusty, no-nonsense character behind it.

Cargo's graduate education was as a freshwater fisheries biologist at the University of Pittsburgh. He was hired in 1950 by Reginald VanTrump Truitt, who had founded the Chesapeake Biological Laboratory around 1919, starting in a small waterman's shed down by Solomons Harbor. When Cargo arrived, it was Maryland's Department of Research and Education, and he was replacing another young scientist, L. Eugene Cronin, who was leaving to start a marine laboratory for the University of Delaware. (When Dr. Truitt retired, Cronin returned to CBL from the laboratory at Lewes, DE. and became CBL's second director, a post he held for two decades. ) Cargo had expected to work on crabs, which he did for 15 years, but he didn't plan to work on sea nettles. In fact, in those days, what was known of sea nettles, their life cycles or where they came from was incomplete.

This lack of interest would continue until a student, working with Cargo, examined the translucent stomachs of sea nettles and found larval fish, worms, shrimp and other crustaceans inside. If nettles are eating the larvae, scientists reasoned ... we can't harvest the adults of these species.

The federal government became interested and between 1963 and 1966, Congressman Edward A. Garmanz pushed a "Jellyfish Act" through Congress.

That's how Cargo became caught up in those tentacles, which would thereafter entangle his career. When grant money became available, he began field and lab studies that clarified some of the life-cycle mysteries and ecological roles of these strange, ephemeral creatures.

Scientists today call the sea nettle Chrysaora quinquecirrha, an entirely different genus from Dactylometra, which is how it was known when Cargo first started in the business. The jellyfish we know start as tiny "polyps," which are sedentary organisms resembling tiny sea anenomes. They live on hard substrates, like the undersides of empty oyster shells or even on sizeable grains of sand. The polyps feed, using tiny tentacles to capture plankton organisms as they drift past on the current. Polyps can also slowly migrate across the substrate, literally "leaving their footprint" or tiny cysts which, themselves eventually grow into more polyps.

From late April to early May, as water temperatures warm toward the mid-60s Fahrenheit (17-18 C) the polyps elongate and begin a multiplication process known as "strobilization," in which a tiny swimming form called an "ephyra" begins to separate from the polyp. Several "peel off" from the top of each polyp. While just a couple of millimeters across, ephyrae feed, as they swim, on other still smaller plankton, and in a matter of days have grown to the shape of tiny, pulsing jellyfish about the size of a pencil eraser.

These free-swimming "medusae" grow rapidly, feeding on the Chesapeake's abundant  plankton, as well as  the immature larvae of many other species.

The sea nettle (Chrysaora quinquecirrha) is about 95 percent water, and is thus suspended almost weightless in the Bay. It swims by "pulsing" or contracting its "bell" cyclically at a rate from once every two seconds to two times a second. It's propelled first upward until its bell bumps the water surface, then turns and both drifts and swims downward, often out of sight before swimming upward again, all the while extending its tentacles, seeking a chance encounter with any prey.