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Extension > Local Extension Offices > Benton > County Horticulture Educator > Articles > Tent Caterpillars Are Back!

Tent Caterpillars Are Back!

University of Minnesota Extension, Stearns County News
May 17, 2017        
           
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns, Benton, & Morrison Counties

 

Tent Caterpillars Are Back!
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (05/17/17) — May flowers and trees leafing-out also brought forest tent caterpillars. Often they are mistakenly referred to as army worms but in fact this time of year those wiggly, hairy worms on your trees or shrubs are likely forest tent caterpillars. 

The forest tent caterpillars hatch when the aspen trees begin to leaf-out in the spring. The caterpillars then spin a silky mat in trees to protect themselves from birds and other predators as well as protect them from temperature extremes that occur at night or on cool, rainy days.  They will feed on a variety of hardwood trees, but are known to feed on other trees and shrubs as well; including roses and apple trees.

Mature caterpillars are hairy, velvety-black with bright blue stripes on their sides. An additional identifying feature is a row of yellow markings resembling a keyhole or footprint running down their back. The forest tent caterpillar feed for five to six weeks starting as early as May and running through June depending on the date they emerge. The caterpillars pupate in a silky cocoon that is about one-inch long in a protected area attached to objects like trees, houses, garages or other structures.  A yellowish-brown moth emerges approximately ten to fourteen days later and will lay eggs.  The eggs are laid in a shiny dark-brown mass encircling a small branch where they will overwinter until the next spring.

Forest tent caterpillars are considered more of a nuisance than a serious pest for trees or shrubs.  Defoliation is typically not significant enough to cause permanent damage or death to a healthy, mature tree. Most trees will replace lost leaves later in the summer.  However, trees and shrubs infested with tent caterpillars look ragged until new growth occurs. The forest tent caterpillar can be a nuisance as they can be found crawling on roads, sidewalks, and homes.

Forest tent caterpillars can be controlled without the use of insecticides.  Removal and destruction of egg masses from trees during winter and removing cocoons in early summer can avoid the use of chemicals and defoliation of trees or shrubs.  In early spring, webs can be removed by hand, stick, broom or a heavy spray of water.  Caterpillars can be put into a pail of soapy water or squished but be aware they may smear and leave marks on painted structures. 

In times of heavy infestation, chemical treatments can be done. Prioritize your ornamental and fruit trees and shrubs, as many larger deciduous trees will recover after feeding.  Bacillus thuringiensis var. kurstai (BT) is a bacterial insecticide that is very low toxicity and is effective if applied when the caterpillars are small; it can be found as Dipel, Thuricide or as Bonide Bacillus Thurengiensis.  Other insecticide products that are effective against tent caterpillars include acephate (Orthene), carbaryl (Sevin), permethrein (Eight), cyfluthrin, esfenvalerate and malathion. Be sure to follow all safety and application directions on the product label.

For more information about the forest tent caterpillar or other insects visit www.extension.umn.edu/garden/insects

 

PHOTO CREDIT: Beth Berlin, University of Minnesota Extension
CAPTION: Small forest tent caterpillars on apple tree

Contacts

Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
adam0062@umn.edu
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