Lots of very hungry caterpillars are munching on Athens oak trees, and University of Georgia researchers want to know why.
The dark gray and brown caterpillar is not some new invasive species from across the globe, but a native known to range from Ontario down to Georgia and as far west as Arizona.
Entomologists in Athens and other eastern cities can’t remember ever seeing so many of them, said Kamal Gandhi, a professor of forest entomology in UGA’s Warnell School of Forestry and Natural Resources.
Homeowners and landowners first began asking Gandhi last year about the caterpillars plaguing their oaks, she said.
It wasn’t in any of the moth books she consulted, but a moth expert at the University of Connecticut identified it as the black-dotted brown moth, Cissusa spadix.
Before now, spadix wasn’t considered a pest. But when thousands of the little eating machines are looking for lunch in the same place, they can do a lot of damage to an oak tree’s leaves in a short amount of time, Gandhi said.
An outbreak in the university’s Whitehall Forest defoliated a big white oak in just four days, she said. But the caterpillars usually don’t completely wipe out a tree’s leaves.
“It’s really varied how much damage they do,” she said.
Since the beginning of April, the leaf-eaters have come back in even greater numbers than last year, she said.
Gandhi can confirm that the hungry caterpillars are in most counties surrounding Athens – Clarke, Madison, Oglethorpe and Oconee – and possibly in nearby Barrow and Gwinnett counties.
Now Gandhi and ecologist Jacqueline Mohan wonder just how widespread the caterpillars are and if they are spreading.
Gandhi would like to hear from anyone in Georgia or other states who might have spotted the moth caterpillars chewing on oaks; her email address is firstname.lastname@example.org.
The caterpillars have a black head and a thin white racing stripe down their sides.
They hide in leaf litter and tree-trunk crevices during the day, then move into oak canopies at night to feed.
“They do seem to prefer white oak,” Gandhi said.
The researchers can only speculate what’s causing the caterpillar population boom.
“We don’t know for sure,” Gandhi said.
They speculate that the moths are taking advantage of two good growing years for oaks.
“We came out of a drought, so oaks grew really well and provided optimal conditions for caterpillars,” Gandhi said.
Warm weather and plenty of fall rain helped oak trees grow, providing lots of food for hungry caterpillars that specialize in oaks.
That could mean more caterpillar outbreaks in the future, judging from some of Mohan’s research. Global climate change could boost oak growth.
To spot the caterpillars, start by looking for oak trees that have been stripped of their leaves, or an abundant scattering of frass (bug poop) on the ground.
The caterpillars will also sometimes come into people’s houses at night. As a defensive mechanism, they will vomit, Gandhi said.
Homeowners can limit damage from the little munchers by putting burlap bands around a tree’s trunk and duct-taping the bottom of the band to keep the caterpillars from crawling through cracks in the bark, according to Gandhi.