HUDSON, Wis. - Trees along the roadside in the area have been sporting what look like giant cobwebs.
Those web-looking structures announce an apparent high mark in the cycle of the eastern tent caterpillar.
"The eastern tent caterpillar is primarily an aesthetic nuisance," said Andrea Diss-Torrance from the office of Sciences Services at the DNR in Madison via an e-mail exchange last week.
"Every year we have a report from someplace in Wisconsin that has an unusual number of tents, but the mini outbreak is typically limited to a small area, often along roads. You would see the same sort of thing in Minnesota," she said.
Eastern tent caterpillars prefer wild black cherries, wild plums, domestic fruit trees and crabapples.
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"Once they run out of their favorites they can move onto (the leaves of) young oaks and maples. Along your roadways, you are probably seeing them on shrubby wild cherries and plums," said Diss-Torrance.
"Our native cherries and plums have co-evolved with the eastern tent caterpillar and typically tolerate the defoliation well. They will put out a second set of leaves in a few weeks. On domestic fruit trees and ornamental crabapples, it is usually a good idea to control them," she said.
Property owners should wait until dark when the caterpillars return to the tent for the best results in eliminating the worms.
"Using rubber gloves or a rake, strip the tent and the caterpillars inside it out of the branch fork and plunge the whole mess into a bucket of soapy water. By the next morning the caterpillars will be dead. This is safe, cheap and works especially well if you are alert and notice the tents when they and the caterpillars are small in early May," Diss-Torrance said.
Insecticides that include the bacteria Btk (Bacillus thuringiensis var. kurstaki) work very well on tent caterpillars. The insecticide should be applied to the leaves as the caterpillars need to eat the Btk to be killed, she said.
The many advantages of using Btk include caterpillars that become ill or die after ingesting Btk are not considered dangerous to birds or other animals that feed on them, writes Jodie A. Ellis, of Purdue University Department of Entomology.
In general, sunlight and other microbes destroy Btk applied to foliage within three to five days, so Btk does not multiply or accumulate in the environment. Btk does not appear to pose any significant threat to human health or to pets, she said in a Q&A article on the Web.
Diss-Torance warned against cutting branches holding the tents or trying to burn the tents off the tree. "You will do far more damage to the tree than the caterpillars ever would," she said.
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The eastern tent caterpillars are finishing up feeding soon and will be leaving the tents and roaming the ground. The tents will remain behind and eventually be weathered out of the branches or can but pulled out of the tree forks if they are bothersome, she said.
"In general these (eastern tent caterpillar) outbreaks are part of a natural cycle, but the causes are not fully understood and probably involved a 'perfect storm' sort of alignment of various factors related to habitat and population dynamics of the insect," said Joe Gathman, assistant professor in the UW-River Falls biology department, in an e-mail message last week.
He said typically the caterpillar abundance builds up for a few years, reaches a maximum for a year or two then quickly recedes. There's no lasting damage to the forest, despite the trees being temporarily denuded of leaves.
"I understand the current outbreak is expected to drop off in the next couple of years, so it may be at its maximum now," Gatham said.
For more information, contact http:/dnr.wi.gov /forestry/fh/ftc or http:// www.entm.purdue.edu/entomology/ext/index.htm on the web.
