Dale K. Pollet, Merrill, Thomas A.
They’re creepy, crawly and wiggly, and some of them sting. Parts of Louisiana have been overwhelmed by caterpillars, according to LSU AgCenter entomologist Dr. Dale Pollet.
"They are hanging from the trees, crawling over houses and fences and on all plants," Pollet says.
Four different caterpillars – the forest tent caterpillar, the eastern tent caterpillar, the buck moth caterpillar and the tussock moth caterpillar – are defoliating several species of oaks, sweet gum and numerous other plants and trees throughout South Louisiana, the LSU AgCenter expert says.
The forest tent caterpillar is a fuzzy blue caterpillar with a series of small keyhole or footprint-like spots down its back.
"The forest tent caterpillars’ primary hosts are the sweet gum and oak, but they will feed on a wide range of plant material from flowers to crape myrtles," Pollet said.
Forest tent caterpillars spin silken threads that are deposited on the trunk and branches as they move about, Pollet explains, adding that their close relatives, the eastern tent caterpillars, actually spin web-like masses.
"When disturbed or blown about by the wind, forest tent caterpillars will hang down from plants on this silken thread – creating havoc around homes and office buildings," the LSU AgCenter expert said, adding, "Once out of the trees, they wander about randomly looking for a new food source."
There are three very visible signs of an infestation – the caterpillars themselves, the disappearing foliage and the small but gradually enlarging black fecal pellets that look like cracked pepper on all surfaces beneath an infestation, Pollet says.
"These caterpillars have been around about two weeks and will be here another two weeks before they pupate and then emerge in May as small buff-colored moths with two oblique tan lines in the forewings; they will be everywhere and are attracted to lights," he said. "They will mate, and the females will deposit their eggs on the branches of host trees for the next generation next spring."
The LSU AgCenter expert said the reason residents may think they are seeing more of these caterpillars this year is just the natural cycle.
"Like all insects, they are cyclic, and this year they are at the top of their cycle," he explained. "This cycle runs on a five- to seven-year period, so that we will probably have a heavy population again next year and then they will gradually decline."
When they pupate, these caterpillars like to wrap themselves in the foliage of the trees in a small white cocoon, according to Pollet, who says during the larval stage there are not many predators or parasites that affect the forest tent caterpillar.
"But in the pupal stage, several birds including the mocking bird and blue jay, among others, will feed on the pupa," he said, adding, "Several small parasitic wasps also attack the pupa."
The egg mass of these caterpillars appears as a dark plastic-looking glob that is wrapped around smaller stems of plants – awaiting the warmth of spring next year to hatch out.
"In the fall, when the trees are bare, these are readily visible and can be easily removed to help reduce the populations on the trees in your yard," Pollet advised.
As for other caterpillars causing problems, Pollet said the eastern tent caterpillar is the yellowish-brown caterpillar with the yellow stripe down its back.
"These are the caterpillars that build the webby mass in the crotch of the branches of the host trees," he said. "These caterpillars emerge from the webbing to feed on the surrounding foliage at night."
At maturity, eastern tent caterpillars are about 2-3 inches long and emerge from their webbing and begin to wander around looking for a place to pupate. They use cracks, crevices and protected areas under the lips of porches, chairs, overhangs and similar areas to spin their silky cocoons.
When they emerge, the adults are small buff to reddish-brown moths with two whitish stripes running obliquely across each forewing.
"The eastern tent caterpillar population is in the process of seeking these pupation sites now," Pollet said, adding, "These caterpillars emerged about two weeks prior to the forest tent caterpillars, and their larval cycle is about over. This population was hardly noticed because of the massive population of the forest tent caterpillars."
Both the forest tent and eastern tent caterpillars are soft and velvety to the touch and do not sting, Pollet says.
"They are good insects for science teachers to use in the classroom. They can be maintained in an aquarium with a screened lid and fed daily with fresh leaves," he said of their good points. "That way children can watch the development of the larvae, molting and then pupation and adult emergence."
The third caterpillar is the white marked tussock moth.
Pollet says this unusual looking caterpillar appears to have a toothbrush on its back, a bright reddish orange head and three long tuffs of black hairs – two near the head and one on the rear end.
"This caterpillar has about three generations that many times overlap, so various sizes larvae may be seen at the same time," he said, adding that these caterpillars have many hosts but prefer for live oaks and wax myrtles. "Like the other two, very few organisms feed on the larval stage, but several small wasp parasites attack the pupal stage, which can be found in the cracks and crevices on the trunks of the host trees."
Many think that this caterpillar stings because of the reaction people have when they appear in large numbers. Pollet said they do not sting, however, but because of the loss or breakage of the dense hairs from the caterpillars’ bodies that float in the air, many people get irritations of the eyes, nose and throat membranes, creating an allergenic reaction that people associate with stings.
The last caterpillar out now is the buck moth, and Pollet cautions this is the one that stings.
This black caterpillar with white and orange marbling has a series of hollow spines that carry amino acid venom. Once touched, these spines break off in the skin – creating an open wound that allows the venom to enter the skin and create a burning, stinging sensation.
This reaction can be broken by treating the affected areas with something basic like ammonia, Clorox, baking soda, meat tenderizer or toothpaste.
"The buck moth is specific to oak trees with an occasional feeding on an alternate host when needed," Pollet said.
These caterpillars have one generation a year – with the larvae pupating about 30 days after hatching.
"They pupate in the leaf litter and other debris at or around the base of the host trees," he explained. "Then adults emerge during deer season, and that’s the reason for the name buck moth."
The LSU AgCenter expert says these black and white adults fly through the woods and neighborhoods in October, November and early December.
"The density of the population gives one a good indication of the potential for next season’s population," Pollet said, adding, "There are no predators or parasites for the larval stage, but the pupae are fed on by many small mammals and birds."
After the adults emerge, they mate, and the females lay their eggs on the branches of the host to hatch the following spring.
Management of all these caterpillars requires spraying to reduce the populations, according to Pollet, who says any pyrethroid (permethrin, Scimitar, Battle, Bayer Advanced Garden with Cyfluthrin) in combination with liquid soap is an effective control measure. The soap is used with the insecticides so that the insecticide will make better contact with the caterpillar.
"These materials are short-lived and are safe in the neighborhood environment and kill the caterpillars nearly on contact," he said.
Applications of the pesticides can be made using a pump-up sprayer for small plants and around the home. To get into the trees to manage a larger portion of the population, Pollet says the use of a hose-end applicator is effective, since it can shoot a stream of spray about 25 to 30 feet in the air – allowing the homeowner to spray into the trees.
"Another good material, but somewhat slower is Sevin, which you also should use use with the soap," Pollet said.
Where trees are very large, the entomologist says it may be necessary to obtain the services of a landscape maintenance company or an arborist to get complete coverage.
"Where pesticides are not wanted, the use of Bacillus thuringiensis or spinosad will help to control the caterpillars but at a slower rate since these materials have to be ingested before the material can begin to work on the caterpillars," Pollet said.
The LSU AgCenter expert said treatment to control the caterpillars may not be necessary since the general feeding of a few caterpillars will not injure trees. "But when populations are dense, there is a potential for the complete defoliation of a tree to create stress on the tree and allow other problems to develop," he said.
For additional information, contact Pollet in the LSU AgCenter’s Department of Entomology at (225) 578-2180 or firstname.lastname@example.org.