An aggressive trespasser the color of antifreeze has threatened for decades to collapse vital Everglades tree islands under its weighty leaf canopy, easily repelling man’s siege of machetes, herbicides and fire.
But researchers hope a handful of tiny winged bio weapons — a moth, a sawfly and a stem borer — will be more effective killers of the invasive plant lygodium, also known as old world climbing fern.
This month, the South Florida Management District governing board approved spending $750,000 to continue projects that raise colonies of insects to attack the flowerless fern, which is a prolific reproducer spread by invisible spores and creeping roots.
A native of tropical and subtropical areas of Australia, Asia and Africa, lygodium has infiltrated multiple Florida habitats, including tree islands, cypress stands, sawgrass marshes, wet prairies and mangrove communities.
But the target of the contract renewed this month is its persistent Whac-A-Mole-like growth in the 144,000-acre Arthur R. Marshall Loxahatchee National Wildlife Refuge in Palm Beach County — the last remaining piece of the northern Everglades.
Water managers estimate the refuge has experienced a 600 percent increase in lygodium in the past 20 years.
“Lygodium spreads extremely fast,” said Andrew Eastwick, a wildlife biologist for the refuge. “If there was no effort to control it, it would completely blanket all of our tree islands, and getting those islands to come back would be almost impossible.”
Eastwick estimates the refuge contains tens of thousands of tree islands, which can be as small as a tenth of an acre or as large as 200 acres. The islands are vital habitats for endangered birds, deer, bobcats, raccoon and other small mammals.
You can’t ‘run away when you hit a wasps’ nest’
The problem with curtailing lygodium in the refuge is the difficulty accessing it — either by helicopter or airboat — and the laborious method used to kill it. Teams of workers in waders and with 40-pound canisters of herbicide on their backs must machete their way into tree islands, cut the climbing lygodium at waist level and then spray it with weed killer. The job includes facing down alligators, snakes and wasps’ nests.
In 2010, the Discovery Channel show “Dirty Jobs with Mike Rowe” accompanied a team in the refuge that was working to remove invasive melaleuca – a similarly difficult task.
“You can’t just run away when you hit a wasps’ nest,” Eastwick said. “You are in a tough situation.”
That’s why an army of lygodium-munching insects is being raised by a United States Department of Agriculture’s research lab in Davie with the help of the contract renewed this month.
It’s not the first time USDA entomologists have been consulted. For about 10 years, the brown lygodium moth and the lygodium mite have been released in the refuge in an effort to control the fern. In the caterpillar stage, the moth eats lygodium leaves. In large numbers, it can defoliate entire plants.
But a 2015 survey of land managers using both insects to fight lygodium found the bugs had limited effectiveness in controlling the fern, which grows vertically, climbing trees and crawling over shrubs to form a thick blanket that smothers native flora.
The fern was first detected in Martin County in 1965, but it went mostly unnoticed until something triggered a growth spurt in the 1990s, said Stephen Enloe, a University of Florida associate professor at the Center for Aquatic and Invasive plants.
Enloe supports using insects to control lygodium and said two species are a good start.
“But having multiple ones that feed on the roots and the stems and the leaves would be fantastic,” he said, noting that procedures to identify and introduce new species into Florida’s ecosystem are more rigorous than in years past.
For example, the water-hogging melaleuca tree was introduced in Florida in 1906 and was used to dry up areas of the Everglades for development and farming.
Now, the state is trying to eradicate melaleuca, and it is illegal to possess or sell it without a permit, according to the Florida Fish and Wildlife Conservation Commission.
“We have learned tremendously from mistakes of the past,” Enloe said. “Our values about conservation have also changed.”
Will a moth and a wasp-like insect be the cure?
The insect program to control lygodium is part of the Comprehensive Everglades Restoration Plan, or CERP.
Phil Tipping, research leader at the USDA Agricultural Research Service in Davie, said insects raised for invasive plant control go through years of testing to ensure they won’t eat other plants.
The insects currently under consideration for lygodium include a moth similar to the one already released, a sawfly, which is in the same family as wasps, and a stem borer that digs into the shoots of the lygodium to feed.
“I’m hopeful and I’m patient,” Enloe said about the new insects. “We live in a culture that wants immediate results, but science is a process, and sometimes a grind.”