Die, Weed, Die!

An alien moth munches an invasive fern into extinction

In the 1979 science-fiction film Alien, the crew of the freighter Nostromo lands on a harsh and barren planetoid to investigate a distress signal. The group discovers the remains of a starship that had crashed, perhaps eons ago, its crew mysteriously wiped out. Quivering in the vessel's cavernous underbelly are thousands of translucent pods. Nostromo's crew members, to their bloody undoing, bring a hatchling back to the mother ship.

The creature turns out to be remarkably adaptable, making hay (and lunch) out of most the crew, all the while growing mightier and craftier. Meanwhile the ship hurtles through space to some new destination where this alien, the so-called perfect organism, will acclimate, consume, and propagate.

Florida's Everglades is now battling its own version of that interstellar invader, an exotic plant so formidable that some researchers have nicknamed it The Perfect Weed. Lygodium microphyllum, commonly called Old World climbing fern, has become Public-Land Enemy Number One.

Owen Richardson
The caterpillars of this moth, the Austromusotima camptonozal, eat 
Old World fern. It's the first insect released against the dreaded plant -- 
but not the last
Christine A. Bennett
The caterpillars of this moth, the Austromusotima camptonozal, eat Old World fern. It's the first insect released against the dreaded plant -- but not the last

The spore-spawning fern is native to most of the tropics in the Eastern Hemisphere, but the Everglades environment has acted as a virtual steroid. As insidious as it is beautiful -- it was brought to the state as a lawn ornamental decades ago -- the fern is a churlish megalomaniac, an herbaceous Donald Trump.

In a relatively short time (scientists date the beginnings of the fern's encroachment to the late Seventies), the climbing vine has blazed its way through the northern Everglades. Once it gains a foothold beside native plants and trees, it smothers them with a dense tangle of string-like vines more than a yard thick. After the trees beneath have died, they crash to the ground under the immense mass of the fern.

Even if the trees underneath manage to hold out, the vines are the perfect kindling for the natural fires that periodically move through. Nothing nearby survives.

Researchers predict if the fern's pugnacious ways were left unchallenged, within a decade it would cover almost all of South Florida's natural areas. And last year's hurricane winds likely helped turn South Florida into a hothouse for billions of spores.

Without intervention by wildlife agencies, Florida faces the prospect of having its beloved Everglades, with its thousands of species of native plants, turned into a vast nursery for a tough, wiry weed that spreads its spores across the landscape like a confetti storm.

Unfortunately for the Everglades -- the only ecosystem of its kind on Earth -- Old World fern may be its worst enemy at the moment, but it's far from its only foe. An estimated 50,000 species of exotic plants have been introduced into Florida. Only Hawaii has more invasives.

The Florida Exotic Pest Plant Council lists 68 invasive species, including Old World fern, that are currently displacing native plants. Almost all of them are found in South Florida, from the familiar melaleuca and Australian pine to the exotic catclaw mimosa and woman's tongue.

State and federal agencies have long attempted to manage them through burning, cutting, and spraying of herbicides. Many who are involved in the eradication effort, however, now recognize the best long-range solution is biocontrol -- introducing the plants' natural enemies -- those little predators who munch away at the invasives in their native habitats. For example, imported from their Australian homeland by scientists ten years ago are legions of bugs and fungi now laying siege to melaleuca in parts of Broward County.

The first salvos against Old World fern were launched this year with the introduction of leaf-eating moths at Jonathan Dickinson State Park and the Loxahatchee National Wildlife Refuge in Palm Beach County.

But halting the rapid spread of a fern as wily as this one is a desperate race against time.

On a hot, humid Friday just before Memorial Day, Stefani Melvin zigzags her airboat through the standing waters of the Loxahatchee National Wildlife Refuge. The sanctuary's biologist, Melvin slows every so often to check GPS coordinates. Scores of white egrets, cormorants, and herons launch into the sky from atop tree islands. The occasional wood stork flaps away lazily.

Six miles out, Melvin nudges the boat beside a little patch of bushes and small trees rising out of the water. "This is how it starts," she says.

There's the enemy, the hungry marauder that threatens to eat the Everglades.

Old World fern looks deceptively meek. Its lavish leaves are slightly curly bright-green oblongs the size of a gel-cap. They fit tightly together on the stem, which is a woody string possessing surprising strength. Compared to the trunk of a full-grown tree, the stem feeding the plant's leaves is a puny toothpick.

Only when you tug on the leafy top vine do you get a sense of the threat. Already the fern has built a deep layer of woody, leafless vine beneath its veneer of fluffy leaves.

The climbing fern is well on its way to covering this SUV-size island. "It's going to kill that wax myrtle tree it's growing on. It's like wire, really tough stuff."

Trying to pull that tangle off the wax myrtle is like pulling a dozen scared cats off a shag carpet, so entwined has the killer plant become with its host. Melvin once found a deer that had made the mistake of running into a thicket of the fern. The animal struggled to its death with its front leg ensnared in the mesh.

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