News Release
May 22, 2007

Tent caterpillars causing problems this spring in Laramie

Western tent caterpillars are abundant in Laramie this spring and are causing damage to trees and shrubs, according to entomologists with the University of Wyoming Cooperative Extension Service (UW CES).

Young tent caterpillars, which produce silk threads, can often be seen in their protective “tents” on the branches of trees and shrubs. The caterpillars and their tents can be removed by gloved hand if the tents are within reach and then destroyed.

Insecticides can also be used to control the caterpillars, which can do a large amount of damage in a short time, said Scott Schell, UW CES assistant entomologist based in the College of Agriculture.

“This spring, the western tent caterpillars have been very abundant in Laramie. The local CES office has been receiving lots of calls about these pests,” Schell said. “As the tents and caterpillars get bigger and the defoliation more apparent, even more people will notice the damage on their plants.”

Schell added, “You don’t want tent caterpillars camping in your trees.”

The caterpillars (Malacosoma californicum) can rapidly defoliate most fruit trees and shrubs as well as ornamental plantings of poplar, willow, ash, birch, mountain mahogany, wax currant and aspen, Schell said.

UW CES Extension Entomologist Alex Latchininsky said, “We have been swamped by tent caterpillar questions the past couple of weeks. The caterpillars are all over Laramie. They are particularly destructive to cotoneaster hedges.”

Adult western tent caterpillar moths are rarely noticed as they are inconspicuous and mainly active at night, Schell said. After mating in the summer, the female moths seek suitable host plants to deposit over-wintering egg masses on branches.

The eggs don’t hatch until late April to early May the following year, usually coinciding with bud break on the host plant.

“After hatching, the little caterpillars stay together and start producing silk threads on a branch crotch for their protective ‘tents’,” Schell said. During the night, the caterpillars move away from the tent to feed on nearby leaves, returning to spend the day in the safety of their tents.

When nearly full grown, the caterpillars disperse from their tents throughout the remaining foliage on the plant to finish growing.

“The last-stage caterpillar migrates away from the plants and forms tan silk cocoons in a sheltered place to undergo metamorphosis. The small, drab-appearing adult moth emerges in early summer to complete the cycle,” he said. There is only one generation per year.

“To control these pesky leaf chewers, you should do a thorough visual inspection of your deciduous trees and shrubs,” Schell suggested. “The small silky tents show up pretty well in the sun and bare branches that surround them.”

If a tree or shrub is lightly infested and within reach, he said, the tents and caterpillars are easy to remove by hands. Wearing gloves is recommended.

“If there are too many caterpillars or they are out of reach, spray can be employed,” he said. “These leaf feeding caterpillars are susceptible to many labeled products with the following active ingredients: Bacillus thuringiensis kurstaki, spinosad, azadirhactin, several synthetic pyrethroids (often labeled as “diazinon replacements”), carbaryl and acephate.”

Schell emphasizes, “Make sure to follow all labels carefully and that the plants you are treating are listed on the label of the product you choose.”

He adds, “Getting in the habit of scouting your plants is a good one for if you can spot the western tent caterpillar webbing, you will be prepared to spot the tents of the forest tent caterpillar (Malacosoma disstria) and fall webworm (Hyphantria cunea), which occur later in the summer, and any other leaf feeding pests attacking your trees and shrubs.”

Persons with questions may contact Schell at 766-2508 (sschell@uwyo.edu) or Latchininsky at 766-2298 (latchini@uwyo.edu).

Contact: Robert Waggener, Editor
Phone: (307) 766-3571
E-mail: robertw@uwyo.edu

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