It's always with a sinking heart that I see the first of them: Blobby, bluish-white, yet as precisely rimmed as if they had just plopped out of a jello mold. With the translucent sheen of arctic ice washed up on a broiling beach, they look unearthly, extraterrestrial. Jellyfish. Couldn't they at least have put off their annual appearance by a few more days? It's frustrating if you're a swimmer like me who hates pools and loves the sea. I'm not one of those madmen who paddle around in the Mediterranean in February as if they were polar bears. It's only in early May that I get up the courage to take the first leap, or more exactly, the first determined run into water that slowly deepens as if testing your resolve every inch of the way - and even then the cold can quite literally take your breath away. Only in the second half of May does the sea in these parts warm up enough for the ordeal of those first few seconds to turn into a - still slightly numbing - pleasure. And then comes June and the water is marvelous. It's crisp and cool, still a far cry from the bathtub temperatures it will reach by August. I get up every morning, have some breakfast, grab a bathing suit, head for the beach, and go for a long swim. For the rest of the day I feel as alive and tingly as if I've started it off with a good massage. Until, that is, the first jellyfish turns up on the beach a few weeks later, like the first dead rat at the onset of a plague. FOR A few days, after the sea has been deserted by almost everyone, I try not to give in. There are jellyfish in the water? Let there be jellyfish. If you do a crawl and keep your eyes open under water you can see their blobs a few feet away, floating slightly below the surface, which is enough to dodge them if there aren't too many - and if you don't, nine times out of 10 nothing happens. I've bumped into many a jellyfish and not been scathed by it. This is because a jellyfish is shaped like a mushroom. Its cap or upper part contains its stomach, reproductive organs and muscle tissue, while in its "stem," which is composed of separate tentacles, are its several mouths, throats, and numerous hairs that secrete poisons and digestive fluids which enable it to stun and eat its prey. It's those hairs that sting. You can bump into the cap head-on, as I've done, and it's no worse than butting a soccer ball. It actually feels like a soccer ball, firm and resistant and not at all the squishy texture you might think it was. To tell the truth, the tentacles of our local jellyfish, Rhizostoma pulmo, are not so fearful either. A swipe from them can give you a nasty burn that smarts badly for a few hours and leaves marks for several days, but the pain isn't as bad as all that, especially if you have something acidic like vinegar handy to swab it with right away. (I've been told by some people that urine works better, but go urinate on your shoulder if that's where you've been stung.) Rhizostoma pulmo isn't like some jellyfish, which can paralyze and even kill you. But how long can you go on dodging jellyfish, especially when every day there are more and more of them, and evasive action becomes harder and harder? Besides, trying to spot a jellyfish under water only works in a calm sea. If the sea gets a bit rough - and there's no better fun than swimming out in the waves and surfing back with them crashing all around you - you can forget about it. The earliest warning a jellyfish will give you then is when it lands on your back, tentacles first. That isn't any fun at all. AND SO after a few days, in which I'm lucky if I'm not stung at least once, I join the crowd that's fled the water and leave it to the jellyfish. Thousands of them. Millions of them. You can't have any idea of how many there are out there unless you see them from the deck of a boat. One after another they float by, a new one every few seconds, a vast, endless minefield of them, stretching for dozens, hundreds, of miles. Where do they think they're all going? According to the scientists, they're mating, which is done by the males releasing sperm into the water and the females absorbing it. It's a huge, traveling, impersonal orgy, and it doesn't sound like any fun at all either. Some jellyfish are beautiful, at least in an aquarium. There's an incredible room full of them in a marine observatory in Monterey, California, that shouldn't be missed if you're ever in the area: Gracefully throbbing, pulsating, jet-propelled creatures of all colors and sizes, some with caps like ladies' bonnets and others helmeted like grenadiers, some trailing tentacles like the tassels of a hula skirt and others sky-diving through the water as if suspended from gaudy parachutes. They make the motions of fish seem clumsy and awkward. But there's nothing beautiful about a lump of slowly melting ice in the sand. A beached Rhizostoma pulmo isn't much to look at. You wouldn't want to take it home and put it on the mantelpiece. And you wouldn't want to eat it, although jellyfish is consumed by some. I once, out of curiosity, ordered a plate of it in a restaurant in Hong Kong, cut into insipid, rubbery strips that tasted like celery forgotten for a month in the back of the refrigerator. No, Rhizostoma pulmo is perfectly useless. And yet there it is, mindlessly hogging the June sea, the brisk, perfect, just-the-right-temperature water that won't return until the end of October. Who made such a dumb, ugly thing? Who set it loose on the shores of this country like an annual D-Day invasion? That's an easy one. Whoever also made the rat, the gnat, the mosquito, the scorpion, the rattlesnake, the louse and the vampire bat. Go complain. You want to swim? Take the chlorine treatment at your local pool. The sea's out of bounds until all those jellyfish get tired of sex and go home.