Delane O'Shields can hear them chewing. Caterpillars, thousands of them, are feasting nightly on her oak trees.
"They are stripping the leaves, but you can't see any nesting. When you go out at night you can hear their droppings coming off the trees like rain. They are really difficult to kill and seem to want to be living in my house," she wrote Monday in an anxious e-mail to gardening guru Walter Reeves.
These are the tell-tale signs of a curious caterpillar outbreak that has defoliated thousands of oak trees from Clarke to Gwinnett counties -- and that's worsening year by year.
Oaks are extremely common throughout metro Atlanta, so a major portion of the canopy is at risk. Healthy trees can probably survive a year or two of nibbling, but unless either nature or science curbs the marauding munchers, they could do lasting damage to one of the most treasured assets in the town that calls itself "a forest in search of a city."
The long, grayish-brown and white-striped caterpillar stumped University of Georgia researchers when it was first discovered destroying oak leaves last year -- they couldn't find its picture in their books on North American species. They sent the boorish bug to moth expert David Wagner, of the University of Connecticut. He solved one piece of the mystery: The nocturnal muncher is the black-dotted brown moth (Cissusa spadix), a species found in the East, Midwest, as far south as Texas, and is considered native to Georgia.
"You are seeing an evolutionary novelty recently acquired by these Georgian populations [of caterpillars]," Wagner said. "It hasn't been known to have an outbreak anywhere else."
That raised even more questions, among them: Why has the black-dotted brown moth changed its look, and more importantly, its eating habits? Never before has the bug been considered a pest.
The scientists' concern grew when the caterpillars returned again this spring in larger numbers, with an even larger appetite. In one instance, the caterpillars defoliated a white oak tree on UGA's grounds within four days.
"It’s very surprising to entomologists because it is a native species," said University of Georgia forest entomologist Kamal Gandhi, who recently has fielded hundreds of inquiries from Georgia residents about the bug. "You’d expect an exotic species to behave this way."
The caterpillars are doing anything but behaving, scientists said. Like a scene from "Night of the Living Dead," they live during the day under leaves on the ground, but come to life after sunset to begin their trek up a tree trunk. They've developed a strong affinity for white, post and red oak trees, munching on the fleshy green leaves until just a skeleton of the leaf remains.
Homeowners report that the caterpillars, perhaps attracted by light, often try to crawl into their homes at night, especially during storms. "I just hope they don’t suck blood or anything gross, or we’re goners," joked O'Shields, who lives on the border of Gwinnett and Walton counties.
Gandhi and others worry that unless the caterpillars are brought back into control by natural predators, such as wasps, pathogens, or bacteria, trees could suffer from repeated defoliation.
"Any tree that gets defoliated a year or two in a row is very much stressed. A weak tree could be killed," said Wagner, who is including Georgia's caterpillar conundrum in his next book.
Gandhi said researchers have experimented with wrapping trees in burlap to protect them from the caterpillars, a tactic that has had some effect. However, it's too late for home and landowners to prevent damage this year, as feeding season will come to a close in the next few weeks.
She is among those waiting to see whether nature will take its natural course in controlling the caterpillars when they wake up from their slumber next March.
"We really don't know much about this insect and so we don't know how to manage it properly either," she said. "It’s a wait and watch game."
(Homeowners who believe they may have an outbreak are asked to contact Gandhi at kgandhi@warnell.uga.edu.)
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