Sure, your cherry and apple trees survived the attack of Eastern tent caterpillars, those icky brown crawly things that were all over door frames, decks, sidewalks and soffits a week or so ago, but don't get too happy. Gypsy moths are coming for your oak trees.
Gypsy moth eggs -- hidden last summer on the bottoms of oak tree branches, and under picnic tables and lawn furniture -- have hatched, turning into caterpillars that feast on the leaves of shade trees from Snow Hill to McHenry.
For now, these caterpillars are difficult to detect because they hide during the day and feed at night, but some time next month, large branches stripped of their leaves will be evidence of their presence.
The two types of caterpillars can be distinguished because they hatch at different times and are different in appearance. The Eastern tent has a black-and-white stripe down the middle of its back and pale blue oval spots along each side. The gypsy moth has five pairs of blue spots followed by six pairs of red spots down its back. Both are about 2 inches long and have fine, light brown hairs.
Heavy toll anticipated
State officials say this might be a particularly bad year for gypsy moth caterpillars, judging from the acreage that has required spraying.
"We've needed to treat 17,000 acres this year," says Bob Tichenor, chief of forest pest management for the state Department of Agriculture. "That's almost triple what we sprayed last year, which was triple what we sprayed the year before."
State crews began spraying insecticides on the lower Eastern Shore last month and are about to finish in Western Maryland, where they have seen evidence of the worst infestation.
Tichenor says it is unclear why tent or gypsy moth caterpillars are more of a problem from one year to another, or from one area to another.
Scientists can predict the following year's gypsy moth outbreak by surveying egg masses on tree branches in the late summer and early fall. Maryland's experts take their cues from the same forests every year.
Robert Rabaglia, an entomologist with the state, says the population is regulated at least partly by the availability of predators, such as deer mice and birds, parasites and a fungus that has wiped out gypsy moth populations in New England but has had less impact here.
Both insects hatch in the spring and feed until they are ready to spin their cocoons. Tent caterpillars feed until mid-May, and gypsy moth caterpillars until late June. The moths that emerge from cocoons are incapable of feeding -- they live just long enough to reproduce and die.
Science run amok
Tent caterpillars are native to Maryland, but gypsy moths were introduced to the United States in the late 1860s by Etienne Leopold Trouvelot, a French entomologist who took them to Medford, Mass., where he was trying to cross them with silkworms to develop a strain resistant to a disease that had destroyed the silk industry in Europe. The moths escaped and their range has spread since.
Gypsy moths, which attach their eggs or cocoons to just about anything outdoors that is stationary for as little as 20 minutes, can be found from Maine to North Carolina and from the Atlantic Coast through parts of Ohio, Indiana, Michigan and eastern Wisconsin.
To halt the spread, the federal government requires people moving from an area of high infestation to one that is not infested to ensure the belongings they carry are free of cocoons and eggs.
"If you park the RV under the shade of the oak tree in Maryland and drive it to visit Aunt Ida in Wisconsin, you're liable to take some gypsy moths with you, so you have to be careful," Tichenor says.
Tichenor and Rabaglia say the tent caterpillar population has been greater this year than in previous years, based on the numbers of calls they have received from homeowners seeking advice. But Mary Kay Malinoski, a regional specialist with the University of Maryland's Cooperative Extension Service, says she has seen little difference.
"We've had a large number of calls [about tent caterpillars], but we get a lot every year," she says. "People notice them because of when they come out, and a lot of people think they are gypsy moths."
Tent caterpillars are more noticeable because they emerge during the day and their white, silky tents appear in the forks of trees early in the spring, when the leaves are little more than buds. They cause less damage than gypsy moths.
Wild and ornamental cherry trees, pecans, beech and willows that tent caterpillars favor have the resources to produce new leaves when the worms have finished feeding and have squirmed off to wrap themselves in cocoons. But gypsy moth caterpillars don't begin feeding until the trees have depleted their leaf-making energy.
"It's like you're building a factory and a bomb goes off just when you're about to start production," Tichenor explains. "You've invested all your money in the factory and you don't have much left to start all over again. But if the bomb goes off early in construction, you still have money left to start over."