But lately, such victories have come at a painful price: crippling injuries caused by the sting of proliferating sea jellies. (See a photo gallery of jellyfish.)

In recent years, swimmers who navigate a Long Island Sound crossing each August have emerged in Bridgeport, Connecticut, with painful, itchy welts from plate-sized lion's mane jellies that bob at the surface.

One man who swam across Catalina Channel in Southern California last year said he repeatedly endured the electric zap of tiny jellies as their tentacles wrapped around his goggles.

While some jellies are harmless, others can be lethal. Though tiny, the venomous Irukandji jellyfish can cause severe cramps, vomiting, and spikes in blood pressure. The box jellyfish is also called