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
Plant scientist Min Rayamajhi has helped develop a small army of insects 
in the battle against melaleuca
Sthephen Ausmus
Plant scientist Min Rayamajhi has helped develop a small army of insects in the battle against melaleuca
FIU professor John Volin has studied Old World fern for six years and 
holds a grudging respect for the plant's amazing adaptability. Top left: A 
sprig mug shot of Florida's Public Enemy Number One: Old World climbing 
fern
Colby Katz
FIU professor John Volin has studied Old World fern for six years and holds a grudging respect for the plant's amazing adaptability. Top left: A sprig mug shot of Florida's Public Enemy Number One: Old World climbing fern

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.

Melvin, an easygoing woman with short blond hair and a deep tan, aims the boat to a nearby large tree island that in February became host to a colony of Australian moths called Austromusotima camptonozal, the first bioagent released in the battle against climbing fern. She steps off into the saw-grass ridge and follows a narrow clearing up to the tree line. "This might be an alligator trail," she warns. "Other times of the year we could probably walk this, but they probably have a nest at the end of that trail. The females will definitely defend the nest, so I try to stay out of their way."

But the killer weed is as much a threat to that nesting alligator as to native plant life, Melvin notes.

And tree islands are as essential to Everglades fauna as a shoreline is to sandpipers and clams. Minute elevations in sea level in the Everglades -- often from small limestone plateaus -- give shrubs and trees a chance to take root where the water would otherwise be too deep. Over time the roots and falling leaves build up and increase the elevation, so the larger islands stay fairly dry even during the wet season. Deer, raccoons, panthers, and of course those nesting gators make the shady underbrush their home. Birds nest in the treetops and dine on the seeds and berries.

It's no exaggeration to say that without tree islands, the Everglades ecosystem would collapse. "Anything that needs dry ground relies on the tree islands," Melvin says under the blazing sun.

Old World fern wipes out tree islands.

It's hard to see it at this water level, but the tree canopy on this island, like many in the preserve, has collapsed under the immense weight of the climbing fern. "It's like this big donut, and then from there it grows out and over the trees on the outside," she says. "It becomes a huge mound of Lygodium." Indeed aerial photos of these islands look like pro football arenas covered in green: The middle is flattened to the ground and the edges sweep sharply upward.

State and federal agencies are already spending millions of dollars a year on herbicides and machete campaigns in a tough, slogging war against Old World fern. At best the eradication campaign is slowing the weed's expansion.

But scientists are pinning their long-range hopes on the doughty little Australian moth that can't get enough of the insidious fern.

State naturalists had traveled to Japan, Southeast Asia, and Australia, finding more than eighteen species of herbivores that dine on Lygodium. They spent one million dollars and seven years looking for, testing, and permitting this first, single moth in order to release it in South Florida. The bright-white wispy creature is a mere half-inch wide from wingtip to wingtip and decorated with wavy brown streaks. Its adult life is short -- three to five days -- but the species's prolific females can lay 100 eggs at a time.

The moth's reign of terror against Lygodium, however, comes during its early life as a caterpillar, whose hearty appetite strips the leaves into skeletons. Eating Lygodium exclusively, it can kill small plants and seriously damage larger ones. If future testing goes well, the moth will be joined by a mite, which also eats leaves and promotes plant disease, and another fern-hungry moth.


If alien plants such as Old World fern are barbarians at the gate, then the Invasive Plant Research Laboratory is among the best lines of defense in this long weedy war. Tucked amid a plethora of college and technical school campuses southwest of Davie Road and I-595, the new quarantine lab is dedicated to finding the right bugs and diseases to maim and kill the worst invaders.

The man in charge is Ted Center, who wears a short groomed grayish beard and speaks in the slow, deliberate cadence of a man who is used to explaining the complex to the unlearned. The research leader's eyes are world-weary -- or perhaps simply showing fatigue from the ongoing move into the new digs.

"There are very few facilities of this quality in the world," he boasts of the lab, which is owned by the U.S. Department of Agriculture, his employer, but sits on University of Florida property. He should know: "I went all over the world to look at every quarantine facility to see what went right, what went wrong."

The lab isn't yet under full quarantine but should be completely operational by midsummer. It's like a set from The Andromeda Strain -- except the airtight isolation zone is for foreign bugs instead of an interstellar virus. The entrance is a series of antechambers with magnetic doors that don't allow passage until all others are sealed. Insects imported to the lab are kept in a receiving room until they've produced offspring, which are then transferred inside. The original bugs, as well as any original packaging, are then destroyed. The air in the lab is filtered heavily enough to prevent any insects or spores from escaping. All liquids drain into a heated sump that destroys anything living.

Five living-room-size greenhouses are attached to the general quarantine lab, which is where routine work is done. To reach the maximum-security lab, which is used for work on plant diseases, you must pass through yet more safety chambers. Thirteen doors separate the outer world from this inner sanctum; an eerie, muffled clank signals you've earned the clearance to move through the next doorway.

"We can't work with viruses or bacteria, but we can work with fungal pathogens, which is mostly what we're interested in," Center says. "They [federal environmental authorities] will give us permission on a case-by-case basis."

The building is a huge leap forward for the dozen entomologists, plant pathologists, and ecologists working here on biocontrol. Until now these researchers have used two small greenrooms at the University of Florida in Gainesville. "It's been incredibly productive," he says. "They've developed over 20 biocontrol agents in maybe the last 25 years. But it was small and too far away. With the invasive species problem getting bigger and bigger, we needed more space."

They will now be able to test several, maybe up to a dozen, different kinds of insects at the same time. "Before, we had to do it one at a time," Center says. "Our limitation had been space and funding; now it's manpower."

Center opens a large glass door into a greenroom, where one of the first experiments is underway. A score of young melaleucas rise up a yard from small black pots. Clinched around their leaves are a series of screen cylinders. Inside each cylinder is a particular breed of fly that carries within it minuscule worms. The fly and worms share a mutually beneficial relationship: The fly lays eggs inside the buds of the melaleuca, which is a source of food for the larvae when they hatch. But the fly also inserts the worms. The tree is tricked into believing the hungry worms are part of its blossom system, and it steps up the amount of nutrients it's sending to the buds.

In essence, the tree wastes valuable photosynthetic energy on swelling buds that will never bloom because the fly larvae will consume them after birth. The worms then re-enter the newborn females, and the cycle begins anew.

The payoff for the enemies of the melaleuca is that the tree's ability to bear seeds is largely stymied.

"We recognized very early on that basically a dead tree and a nonreproducing tree are the same thing, from a biological standpoint," he explains. "If it's not producing seed, it's not doing any harm. You don't really have to kill the tree to control it."


Biocontrol has a long and reliable history behind it. Aquatic invasives were targeted in the Sixties, primarily because few herbicides have been licensed for use in water. Alligator weed, a green, spaghetti-like plant, was a particular problem for boaters and fishermen. "Three insects were introduced to control it," Center says. "Within a few years it was no longer a problem, although it's still a problem in the Mississippi Valley, where it gets too hot for these insects to survive. Alligator weed is still here at a low level, and so are the insects. When the alligator weed pops up, so do the insects."

Center's work with biocontrol began with an aquatic nuisance called water hyacinth, a plant that sprouts beautiful flowers and kills everything beneath it by cutting off sunlight. One insect eventually released on the hydrilla offered a hard lesson about just how specialized these herbivores are to their native terrain. In this case the scientists, after years of testing and seeking government approval, released an Australian weevil that feeds on the stems of the hydrilla.

"This weevil looked really effective because it would burrow down the stems, mowing them off four or five feet below the surface," Center recalls. "We tested it; it was safe; we released it; never saw it again." That happened repeatedly. What they eventually surmised was the weevil larvae continued down the stem to the lake bottom. The species had apparently adapted to extreme wet/dry seasons in its outback homeland, so when its larvae become fully grown, they simply wait for the water to dry out -- a seasonal extreme that doesn't occur in Florida. So it was back to the drawing board.

Still, even if you find the right bug for the right place, biocontrol takes patience. Although it's a very general rule of thumb, establishment in the wild is considered successful only after five generations have come and gone -- which is judged simply by the amount of time that's passed. It can take years to build up enough insects to reach a critical mass that can debilitate its host plant. And some insects just aren't as inclined to spread as others.


Melaleuca has long been recognized as a problem in South Florida, but it's now the poster boy for biocontrol success.

Like so many invasives, it was brought here from Australia as an ornamental lawn tree in the early Twentieth Century. With waxy green leaves the size of a small banana peel, it was fast-growing and made an excellent full hedge. Nicknamed the paper-bark tree, it's far from attractive once it reaches maturity, however, when its whitish bark peels off in onion paperlike sheets.

It quickly made its way into the wild. Nurserymen helped the spread after realizing they could save time by sowing the seeds in marshes rather than in planters. One early nurseryman chartered a plane and dumped cupfuls of seed onto the marshes. In the Thirties it was spread aerially over the Everglades in the mistaken belief it was a way of drying up "useless swampland." It grows extremely fast. Center recalls seeing seeds reach twenty feet in eighteen months in ideal growing conditions.

By the Fifties, melaleuca had become a problem tree. Once it catches hold in an area, the trees form a jam-packed canopy that shrouds the understory in near darkness. Nothing grows beneath the thickets -- except small melaleucas. An acquaintance of Center's recalls once seeing a spooked deer run toward a melaleuca stand, only to bounce off it because it was so dense.

The trees alter the landscape of the Everglades, especially when it comes to fire, which is a natural part of the ecology. Normally the wildfires are "cool," which doesn't kill the native plants. But when the flames hit melaleuca -- an invader that didn't evolve with the fires -- the flames become intense as they catch the paper-bark tinder and kill everything near it. If a melaleuca dies, it drops its seeds -- roughly 60 million in an average tree. Natural vegetation has a hard time competing with it.

Largely in response to the melaleuca and a handful of other invasives, the Florida Exotic Pest Plant Council was formed in 1984 by control agencies, plant nurseries, and environmentalists, and it soon held a symposium that included the Agricultural Research Service, which is the USDA's in-house research arm. "Most of the people involved originally had an environmental motivation," Center recalls. "Some economics followed because the only way they could control melaleuca was to cut a ring at the bottom of each individual tree and use full-strength herbicide. There could be 10,000 trees to an acre, and the cost was $4 a tree. So you were talking about $40,000 an acre."

The USDA had already established a lab in Australia as part of the hydrilla biocontrol effort. "Our funding was running out for that, and we had staff over there, so we just changed gears to look for bioagents for melaleuca," Center says. More than 400 species of insects feed on the tree in Australia, and the researchers began narrowing the field to insects that would eat melaleuca only. The tree contains the same kinds of oils as a eucalyptus tree, which are basically a defense against herbivores, so anything that eats it is usually specialized. That's good, because it reduces the chances the insects will be interested in Florida's native plants.

Far from being a crap shoot, it's quite predicable what insects will eat, Center asserts, as he opens a thick scientific treatise called Insects on Plants. "People get the idea that we're going to release an insect and it'll eat up the melaleuca and then it'll go eat everything else that's green. That's not the case. If it takes out the plant it feeds on, their populations usually crash." He estimates biocontrol scientists worldwide have released about 300 species of insects against roughly 150 species of plants -- with virtually no unintended consequences.

In 1997 a grayish weevil that looks a bit like a tiny horny toad was released against the melaleuca. A plant louse, which in its nymph form sucks the tree's juices and injects it with a toxic juice, was released in 2002. If you wonder how anything so small could ever raze hundreds of acres of 200-foot melaleucas, Thai Van and Min Rayamajhi have developed an outsize show-and-tell. Plant physiologists at the lab, they've been monitoring an experiment for eight years just west of Highway 27 in Broward County. A sweeping stand of melaleucas has overgrown scores of acres owned by a utility company, which has killed many trees with herbicide. New saplings are eagerly shooting up to replace them.

In the center of the property, however, lies a roughly twenty-acre section that's been left untreated. Deep inside is the test plot Van and Rayamajhi routinely monitor to measure the effects of the bioagents.

They weave their way about 50 feet into the thicket. "Look at this one," says Rayamajhi as he grasps a small melaleuca shrub with a rusty color on its leaves. "It got hit by disease, and it's trying to grow back. The rust is disease. This one got hit by weevil."

Van picks up what looks like a miniature brown cob of corn. This is the melaleuca seed fruit. Each of its hundreds of "kernels," which are the size of a needle head, can hold about 400 seeds.

Even the tallest trees are at risk from the good weevils. As trees grow bigger, they require more nutrients via photosynthesis. Thus a large canopy of leaves is essential. "The food production goes down because the insects feed on leaves and disease hits the trees," Rayamajhi says. "The tree diverts its energy to fight the insects, and then it doesn't have enough food to reproduce. Then they'll die. People wonder how little bugs can kill these big trees, but they're actually very vulnerable."

Their research has been enough to convince even skeptics that bioagents are a real alternative to spraying. "We needed to convince the state agencies that this was a long-term alternative to chemicals," Rayamajhi says. "At the beginning we didn't have the funding to disperse the insects, but now they've reallocated some of the chemical funds to insects."


In late 2000, John Volin, an infectiously energetic plant scientist at Florida Atlantic University, began looking at the steady growth of Old World climbing fern. Little was known about its biology. Not until 1978 was its spread scrutinized by two scientists, who found it growing near the shoreline in southern Martin and northern Palm Beach counties. They concluded the spore-bearing plant was a cause for worry.

No one became worried.

The fern, however, spent the next fifteen years diligently establishing itself in the undergrowth, then climbing upward, and finally coiling around tree branches and leaves. Starved of sunlight, the trees slowly died. The South Florida Water Management District, a state agency that's a front-line warrior against invasives, began aerial surveys of the fern in 1993 from coast to coast at 500 feet above treetops. By the end of the decade, the water district had data indicating the fern had spread to Florida's west coast and was overwhelming the tree islands of the Loxahatchee National Wildlife Refuge in south Palm Beach County.

What, Volin wondered, was the Everglades facing?

Using the data collected between 1978 and 1999, Volin devised a computer model to project the spread of the climbing fern by the year 2014. Despite knowing how rapidly the plant had multiplied, Volin was stunned by what he found. The model revealed the fern will have covered almost all the Everglades in Palm Beach, Broward, Hendry, and Collier counties. Substantial portions of Martin and Glades counties will have been covered, and the infestation will have made deep inroads into Everglades National Park in Miami-Dade County.

Volin's findings seemed too dire to be true. "I said, 'Hell, we can't share this,'" Volin recollects. So before announcing the findings in 2002, Volin and his research assistants double-checked the reliability of his prediction through painstaking marches through the Everglades. "I feel strongly that, as a physiological ecologist, when we're doing predictions -- whether it's about climate change or, in this case, an invading species -- you don't want to overstate it," Volin says. "It's like saying the sky is falling. You don't want to do some dire prediction, only to eat your words later on."

No one's calling Volin a Chicken Little.

Don Schmitz, with the Florida Department of Environmental Protection's invasive plant bureau, estimates state agencies are spending more than two million dollars a year to combat Lygodium, about eight times more than five years ago.

The Loxahatchee Refuge recently received four million dollars from Congress to fight exotics, Melvin says, and the threat of Old World fern certainly helped loosen those purse strings for tree triage. "There will be aerial spraying of islands where there aren't any native plants left and follow it up with a ground crew on the perimeter," she says.

Volin, who possesses a bantam build, impressively full goatee, and piercing eyes, is overseeing another ambitious year-long project, funded by the water district, to hunt down incipient sporelings of Old Word fern in the east-central part of the Everglades. His research team will visit each of the roughly 500 islands and, using a GPS device, record each sighting of the fern. The management district will then send out contractors who will locate the exact spot and treat the plant with a systemic herbicide that completely destroys it. It's an endeavor analogous to bicycling across the U.S. to visit every 7-Eleven: They're everywhere and you never know where the next one will spring up. Just how much this will cost won't be known until later.


On a partly cloudy morning in late May, Volin and three other researchers haul two airboats an hour south of Davie to a public dock along Tamiami Trail. This is the driest month in the Everglades. The water covering the vast expanse of grass surrounding tree islands has slowly receded during the desiccated winter months, and the routine rainstorms of the tropical season have yet to begin in earnest.

The airboats are relatively small three-seaters, each driven by a cacophonous twelve-cylinder aircraft motor. The two boats weave northeasterly for about twenty minutes, sometimes crossing patches of slough that are little but mud. They pull up to a high stand of saw grass on the east side of a tree island. The real work begins on foot. Dressed in long-sleeve shirts and long pants, they begin the fern hunt by stepping off into water that's just under two feet high.

This is the first foray into the glades for Mary Ann Furedi, a new researcher who's only recently moved from West Virginia, where she walked mountainous terrain studying ginseng. A twentysomething with longish dark blond hair, Furedi will head this new project, but she and her team will go far beyond the tasks contracted for by the water district. Among other things, they'll be trying to identify "bio-indicators," which are plants or formations that act as hospitable hosts to a particular invasive species. When such a correlation is made, a bio-indicator creates a kind of shortcut for locating invasives and determining their reproductive and growing cycles. (Melaleuca, for example, is a sucker for spots that have been disturbed by fire.)

The saw grass crackles as the party of scientists wends its way through the serrated blades. A red-tinged bird chatters angrily at the intruders. The ten-foot perimeter of saw grass gives way to muckier ground with waist-high shrubs. If cave explorers go spelunking, then Everglades surveyors must go spelooshing, because that's the sound of extricating one's foot from the muddy soup.

The interior of the island is cordoned off with a thick wall of willows, vines, and holly. The plan is to use a compass and walk a straight east-west line across the island, keeping one eye out for Old World fern and the other on things like a ubiquitous prickly concertina wirelike vine that would sooner decapitate visitors than allow them passage. Furedi and her research team of three or four will spend four or five days a week trekking through tree islands like this.

One bio-indicator for Old World fern appears to be "moss collars." These grow at the base of trees and as high as four feet from the ground. So when the four researchers chance upon a decomposing log with a crewcut of green moss upon it, they crouch down under the dusky canopy. There they spy minuscule sporelings in the first stage of spore growth. Furedi takes a small plastic container from her backpack and inserts a chunk of moss-laden wood. It's the closest thing they'll see to Old World fern today.

Back in the research lab, Volin will grow the sporelings. He's conducting the same experiment in Australia, using that country's different soils. In the end, he hopes to learn if the soil has some effect on their life cycle.

So far the news is not good. This is one malleable plant. The fern is something of a sex addict, having evolved as a bisexual that can germinate its spores in any of three ways possible for ferns. The first spore to germinate in a new area is almost always female, researchers found, which then produces a pheromone that transforms surrounding spores into males.

Most ferns are very particular about moisture levels during germination; this fern has a more "whatever" attitude. It's not picky about light either; it can grow in dark shadows or in full sunlight atop trees. "This is an incredible plant," Volin enthuses. "The question is: Why is it not invasive in its own native area?" he poses. "We don't know that."

In the coming few years, the battle against Old World fern will be mostly waged with conventional weapons: herbicides, pruning shears, and elbow grease. But at the front line, soldiers know ultimate victory calls for greater weapons than those.

"The best hope we have is biocontrol," says Melvin, who stands at the edge of the moth-populated tree island. A wall of thick ferns dwarfs her. There's no sign of the fern-eating moths today, but it's a big island, and the tiny insects can't have made much headway yet. Who really knows how well these winged warriors will do in the war against Old World fern?

They're a long way from home, and their enemy is so very well entrenched. And reproducing fast.

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