IF AMERICA is a melting pot, then Florida is a bubbling cauldron -- one that gets zanier every year as more and more newcomers pour in. We're not talking about people, however; these new arrivals are exotic animals, insects and plant life imported to the Sunshine State by accident or design and turned loose to thrive in the benign climate.

For the past few years, humans have been moving to Florida at the rate of 1,000 a week. But the animal, bug and plant parade has done even better, turning the state into more of a biological zoo than ever. Recent imports include flying cockroaches, hissing cockroaches, poison toads, walking catfish, piranhas, metal-eating termites, coyotes and monster trees that choke out every living thing in sight.

Such past biological mistakes as importation of the kudzu vine and the water hyacinth pale when compared to the newcomers. Even hydrilla, the aquarium plant that now clogs rivers and lakes, is only a minor nuisance alongside the Brazilian pepper tree and the Melaleuca tree.

These plants from hell are almost impossible to kill. Their spread is so rapid that state biologists can't even quantify the growth rate. Tampa Electric Co. has spent more than $150,000 trying to clear a 10-acre plot of pepper trees during the past year. After manual removal and herbicides managed to clear only one acre last summer, the company this year turned to a $180,000 "Big Brown Bear" land-leveling machine.

The pepper, with its small red berries, looks innocuous. Yet the tree makes humans sneeze and their eyes water. The berries are toxic to birds and wildlife. The pepper shoulders its way into coastal areas, crowding out useful native plants and setting up a canopy that blocks out the sun, while the roots hog precious Florida groundwater and deny it to other plantlife.

Its companion, the Australian Melaleuca, is even worse. It sprouts flowers with a rotten, nauseating stench, generates allergies and spreads a choking canopy. But don't try to burn this tree -- it literally explodes, casting its seeds over a wide area giving it yet another way to drive out useful plants.

Florida has always had these bizarre imports. Somebody's bright idea becomes a castoff, and suddenly it takes over. Biologists estimate there are 400 exotic plants growing wild in central and south Florida.

Unfortunately, none of them -- plants, animals or insects -- stays put. Bufo marinus, a huge poison toad that produces a dangerous hallucinogenic venom, was originally imported into south Florida 30 years ago to eat insects that prey on sugar cane. The toad has now been spotted as far north as central Florida, eating anything it feels like.

Certain deviant youths have taken to "toad-licking" for cheap thrills despite the fact that the toad toxin is known to be fatal to small animals like dogs and even to humans, if ingested directly. Get a shot of the toad's milky bufotoxin in your eyes, and it's worse than mace. Yet Florida pet shops sell bufos to collectors.

It was a Florida pet dealer who recently imported some banned Madagascar hissing cockroaches and turned them loose when he was told they were not allowed. Heaven only knows where their progeny will show up or when. Meanwhile, mid-Florida continues to scan the countryside anxiously for the advance of the Asian cockroach -- a species that travels in herds, becomes active at night and flies or jumps toward the light, making picnics and outdoor camping all but impossible.

First spotted in Lakeland in 1985 after apparently arriving by ship, the Asian roach now infests an estimated 5,000 square miles. It can crossbreed easily with the common German cockroach (which is immune to most pesticides) and already resides here in abundance, along with the ubiquitous native "palmetto bug" and at least 50 other varieties of roach.

The Asian roach is moving at jet speed compared to the more publicized African killer bee, which escaped from a Brazilian laboratory in 1957 and after 30 long, slow years is expected to cross the Mexican-American border this year and reach Florida in 1994.

South Florida, and perhaps beyond, is now home to the fierce Formosan termite, which can eat 15 varieties of wood as well as utility poles and railroad ties, according to the Wall Street Journal. Reports from Hallandale near Fort Lauderdale say the Formosan imports are driving out the local termites and have encircled high rises, even gnawing into copper pipes. Their average colony hosts three million termites, 10 times as many as an average domestic termite colony.

So far, the walking catfish hasn't hiked too far north, but it still manages to haul itself out of canals and streams to search out better environments. Since south Florida canals, lakes and streams have already been despoiled by hobbyists who dump such aquarium novelties as piranhas, Oscars and fighting fish, the walking catfish may need to move north sooner than expected.

In Dania, also near Fort Lauderdale, parrots and parakeets -- some pet store escapees, others abandoned pets -- are now breeding in the wild and producing a lot of unearthly squawking.

Near St. Petersburg, animal-protection people continue to search for boas and pythons living in the wild. Several more than six feet long were found in 1989. In south Florida, an abandoned 22-foot reticulated python was found living under a house and consuming family pets for dinner.

And now coyotes -- coyotes! -- have been sighted in Florida cattle country. No one seems to know how they got there from their native West -- or just what they portend for Floridians, aside from a new nocturnal noise.

Some anti-growth Floridians think that all this floral and faunal activity may help slow the torrent of humans moving to the state -- just as horror stories about the native alligator impeded development in the old days. In fact, the gator itself is back; after three decades of protection as an endangered species, it is alive and well and can now be hunted legally. A rare spring drought this year even led state authorities to warn that gators were showing up in yards and developed neighborhoods to seek water or places to mate.

On the other hand they may just have been trying to get away from Bufo marinus or some of the other recent arrivals.

Jerry Blizin, a retired Washingtonian, lives in Tarpon Springs, Fla.