But with this year’s early spring, the caterpillars are marching earlier and in greater numbers, said UGA ecologist Jacqueline Monahan.
“They are a month early and in just totally crazy numbers,” said Monahan, whose lab has been gearing up to study the impact of the dark gray and brown caterpillar.
The caterpillar, the larval form of the black-dotted brown moth, or Cissusa spadix, is a native species with a range from Georgia as far north as Canada.
But over the past couple of years, the caterpillar has been showing up in big numbers, with outbreaks in Alabama, North Carolina, South Carolina and Georgia, including Athens and surrounding counties.
Last year, during an outbreak in UGA’s Whitehall Forest, spadix caterpillars completely defoliated a white oak tree in just four days, said Monahan.
This weekend, Monahan and others discovered the little crawlers have returned to Whitehall Forest — almost exactly one month earlier than last year, and in what looks like even greater numbers.
Researchers hoped that a parasitic wasp that preys on the caterpillars might also multiply, helping keep the caterpillars in check. More wasps do seem to be out this year, but not enough to make much of a dent in the teeming caterpillar population, she said.
The spadix caterpillars hide away in the leaf litter on the forest floor and in crevices in tree trunks during the day. They travel at night, and sometimes move through the trees in such multitudes that their collective droppings, or frass, sounds like a gentle rain, she said.
They sometimes come inside people’s houses at night, and will vomit as a defense mechanism, she said.
The caterpillars have a black head and a thin white stripe along each side.
Researchers don’t know why the caterpillar has emerged earlier, but they believe global climate change may play a part.
Several studies have show that trees are responding to warmer temperatures by leafing out a week or so earlier than they did 50 years ago. And like the plants, many insects are emerging earlier with the warmer temperatures.
Migratory songbirds help keep insect populations down when they return in spring, but the birds are lagging behind — many songbirds time their migrations to the amount of daylight during the day, not temperature, Monahan said.
Homeowners can slow down the caterpillar’s munching by wrapping burlap bands around a tree and duct-taping the bands down, said Kamal Gandhi, a forest entomologist with UGA’s Warnell School of Forestry and Natural Resources. Some have tried another technique, smearing Crisco around the bottom of oak trunks.