Invasion of Fire Ants Poses New Threat to Area Wildlife
For decades, biologists have struggled to save Southern California’s fast-disappearing birds, reptiles and butterflies from encroaching homes and malls.
They have lobbied to create nature preserves and to save snippets of coastal wetlands as havens for rare shorebirds.
Now a surprising threat is looming on the horizon--not the customary lineup of yellow bulldozers but millions of swarming red ants.
Some experts fear that the red imported fire ant that recently invaded California could “simplify” the local landscape. In short: The ants could prey on other insects, toads and baby birds still in their shells, posing one more threat to wildlife already endangered by disappearing habitat, pollution and road building.
Since the ant infestation was discovered in Orange County only last fall, scientists caution that its effect on wildlife remains uncertain. But the destruction wreaked by fire ants in 10 Southeastern states and Texas clearly makes them nervous.
“I would have to judge them a very major problem, if they become widely established,” said Dan Simberloff, an internationally known bioinvasion expert at the University of Tennessee at Knoxville.
And while California officials this week are due to announce a fire ant control program, one renowned expert is pessimistic. Edward O. Wilson, a Harvard University biologist whose early fire-ant research is legendary among entomologists, cautioned that eradication efforts in the South decades ago cost more than $100 million and failed to stop the ants’ advance.
“It would be very difficult to seek out all the fire ant mounds and get them controlled,” Wilson said. “It may be too late.”
He emphasized the ants’ remarkable ability to spread. “It’s a little bit like cancer, or a bacterial infection.”
To date, most of the public furor over the fire ants’ arrival has focused on human health threats, since their fire-like sting can be fatal to those few people allergic to them. The threat of painful stings could alter the outdoor lifestyle of Southern Californians, forcing people to wear shoes in their backyards and search lawns and golf courses for telltale fire ant mounds.
Faced with such concerns, the state Department of Food and Agriculture is considering deploying a pesticide called fenoxycarb in Orange County that works as a growth inhibitor on the ants, curbing their ability to grow shells. One possibility: applying fenoxycarb from planes or helicopters, perhaps on corncob grits with bait to attract the ants.
Fenoxycarb is known to be highly toxic to some fish and aquatic invertebrates.
This creates a thorny dilemma for wild-land guardians in Orange County, who wonder which is the lesser of two evils--the fire ant or wide-scale use of pesticide to control it.
“This is a tough one,” said Trish Smith, a Nature Conservancy biologist and land manager in Orange County.
With about 100 plants and animals either proposed or listed for protection under the federal Endangered Species Act, Southern California already is labeled a “hot spot” of extinction worldwide. So California scientists are increasingly alarmed by news that fire ants have infested Orange County and parts of Los Angeles and Riverside counties.
They are all too familiar with the stories from states like Florida, Alabama and Texas, where some researchers have blamed fire ants for harming animals from tortoises to rabbits to white-tailed deer fawns.
Fire ants can prey on other ants and insects that are much-needed food for toads and lizards. Some researchers believe that the ants may have led to the virtual disappearance of the Texas horned lizard from the eastern part of that state. Fire ants have even been observed attacking nestling baby birds pecking their way out of shells.
Such incidents do not necessarily mean that fire ants could lead to significant population decreases among rare birds in Southern California, some scientists said.
“These things are notoriously hard to prove,” said fire ant expert Walter R. Tschinkel, professor of biological science at Florida State University. “To show that one population is fluctuating at the expense of another is very, very difficult.”
But some California scientists worry that rare birds and other threatened creatures--including federally listed endangered creatures like the arroyo toad and the Pacific pocket mouse--are in for a frontal assault.
“The species that are already fragmented, those are the species that are going to have the hardest time if fire ants get into their habitat,” said Robert Fisher, a research ecologist with the Biological Resources Division of the U.S. Geological Survey and a conservation scientist at San Diego State University.
He said that since the region features grasslands and chaparral rather than tall forests, most native creatures live on or in the ground.
“Anything that nests on the ground, in the ground or lives on the ground, is potentially at risk,” Fisher said.
Facing the hard choice are overseers of some of Orange County’s last remaining wilderness areas--spots like the National Audubon Society’s Starr Ranch Sanctuary and the 1,200-acre Rancho Mission Viejo Ecological Preserve, both in the southern part of the county.
“It’s a delicate balance to decide what is better,” said the reserve’s executive director, Laura Cohen.
“Things are so complicated now, because there’s so little we know, and there’s so little left to protect,” Cohen said. “And these sorts of decisions, which should take some time, have to be done so quickly because of the immediacy.”
To date, Cohen has not seen any signs of fire ants, though they have been found at a nursery and a golf course in nearby San Juan Capistrano. And state agriculture inspectors have been so busy searching for ant mounds in residential areas that they have not yet had time to scrutinize the county’s wilderness.
But Cohen and others are worried by studies of how fire ants have harmed wildlife in the South. One researcher in southern Alabama blames fire ants for the decline of the common nighthawk, common ground dove and Eastern meadow lark. Another researcher documented fire ant predation on least tern chicks. The fire ant also has damaged other ants, such as the harvester ant.
Craig Allen, a research wildlife biologist from South Carolina, describes fire ants moving into a diverse community of 30 species of ants--reducing it to only a few species.
“What you’re having is a huge change in energy flow from a diverse community to fire ants,” he said.
Potential fire ant damage to ground-nesting birds, meanwhile, is worrying those trying to protect endangered and threatened California birds such as the gnatcatcher, the California least tern, the Western snowy plover, the least Bell’s vireo and the Southwestern willow flycatcher. All five birds are protected by the Endangered Species Act.
“It might be a little early to know, but it’s certainly a scary proposition,” said Loren Hays, senior wildlife biologist and staff ornithologist at the U.S. Fish and Wildlife Service. For instance, reports of ants harming least terns in the Southeast may not bode well for California’s endangered terns.
“If they can do it there, we should prepare for a problem here,” Hays said. But “I think it’s a bit too early to push the panic button.”
Others agree that California is something of a wild card where fire ants are concerned. The ants relish water and irrigated lawns, but no one can say for sure if they will flourish in drier climes like chaparral and coastal sage scrub. In short: Wetlands creatures may be more at risk than sage-scrub-dwelling gnatcatchers.
“No one has the experience in this situation--no one at all,” said Les Greenberg, a postgraduate researcher in entomology at UC Riverside.
Whatever the outcome, experts agree that Southern California wildlife does not need a new enemy.
“The real threat in California is not fire ants, but habitat loss,” Tschinkel said. “The fire ants on top of that could exacerbate an already bad situation.”