Several different species of jellyfish inhabit the Chesapeake Bay and its tributaries. Because jellyfish thrive in temperatures between 78 and 86°F (May through October) and in brackish (slightly salty) waters, it is possible to somewhat predict where and when sea nettles are likely to show up. With no brain to guide their actions, jellyfish depend on tides and currents to carry them to their food. Because of this, one way to minimize an encounter is to avoid swimming or boating along windward shorelines or up creeks during a rising tide.

The most common jellyfish in the Bay is the white stinging nettle. They are recognizable by their gelatinous, umbrella-shaped bells and long, trailing stinging tentacles. The milky white bell can

grow to about 4 inches in diameter and up to 24 tentacles can hang from under the bell.

During the summer months, you are also likely to encounter Moon jellies on the Bay. These clear, fragile swimmers propel themselves through the water by moving their large bell in a waving motion. Four horseshoe-shaped markings in the center of its bell and four short feeding arms distinguish it from a stinging. Although Moon jellies are relatively harmless, their sting can still cause minor skin irritations.

Comb jellies have no stinging cells and are not true jellies. They are propelled through the water by eight comb-like structures (cilia). The cilia bend light like a prism as they move, causing these jellies to glow in the dark and in bright light. They are sometimes referred to as "jelly blobs." In recent years, a few Portuguese man-of-war have washed ashore in the southern Bay. The Portuguese man-of-war is sometimes referred to as the "blue jellyfish," but it is actually not a true jelly. Nevertheless, the Portuguese man-of-war has an extremely painful sting that is much like that of a jellyfish.

Jellyfish are related to other creatures, such as sea anemones and corals, which use stinging cells for feeding and defense. A jellyfish sting is like a thousand tiny spears injecting poison in you all at once, which isn't far from reality. Jellyfish tentacles discharge tiny spear-like structures filled with venom into your skin upon contact. The stings are painful and may create a rash, but they are rarely life threatening, particularly from the species typically found in Chesapeake Bay.

If you are stung, apply salt water, not fresh water. Applying fresh water will cause the stinging cells to become agitated, resulting in further pain. Next, douse your skin in vinegar as soon as possible. Finally, apply heat (not ice) to the injury, which actually reduces the activity of the venom.