Webworm infestation

Asked April 2, 2015, 8:19 PM EDT

We have a horrible infestation of webworms but they're not in the trees; they're covering our mailbox, garage & have moved over to the house. This is the second day. We can barely go in & out of the house. They are everywhere! How do we get rid of them? How long will this last? How much damage will they do to the structures & our outside plants on the patio, etc.? Thank you for your help.

Liberty County Texas

1 Response


Tent caterpillars attack several kinds of broad-leaf trees and shrubs and produce unsightly webs, or tents, which can detract from the home landscape. These caterpillars can defoliate trees, stunting their growth and making them less vigorous. They can also be very common and thus a nuisance as they move around the exterior of a home. One of the keys to eliminating tent caterpillars is early detection.

In late spring or early summer, female moths deposit egg masses on tree trunks or encircling small twigs. These egg masses remain on the trees during most of the summer, fall and winter.

Caterpillars, or larvae, hatch from the eggs in the early spring about the time that the leaves on their host plants emerge and feed on new leaves.

Control programs should be based on the need to eliminate defoliation, unsightly webs and/or nuisance from caterpillars. You may need to use a combination of cultural and chemical techniques to control tent caterpillars.

Cultural control. During winter pruning, inspect the trees for tent caterpillar egg masses. These masses are swelling on small, bare twigs. Through normal pruning, you can often remove tent caterpillar eggs before they hatch. Prune twigs containing webs when you first notice them in the spring. If they are in areas where pruning is undesirable or impossible, you may destroy the tents by hand. To destroy the web, use a long pole or a high-pressure water hose, especially in hard-to-reach areas. Burning the web and caterpillars is hazardous and no more effective than the above techniques. Kill caterpillars knocked from the tree or crawling on a patio or around the home by crushing them or placing them in a bucket of warm, soapy water.

Biological control. Beneficial insects can help reduce populations of tent caterpillars. Parasitic wasps, birds, lizards and other insect such as assassin bugs also feed on tent caterpillars and help reduce their numbers. Take these beneficial insects into consideration when choosing a chemical control method.

Bacillus thuringiensis, or Bt, is a biological insecticide that works best on younger, smaller, caterpillars. Bt is selective in that it targets only caterpillars and is relatively harmless to fish, birds and warm-blooded mammals. Because Bt kills all kinds of caterpillars, use it carefully around butterfly gardens. When using Bt, you must cover the leaves thoroughly to ensure that the caterpillars will ingest enough of the toxin for control.

Chemical control. Before deciding to spray for tent caterpillars, consider that although individual leaves that have been fed upon will remain damaged, trees that have been defoliated early in the season will usually put on new leaves. It is useless to spray if tent caterpillars have been allowed to feed and have completed their development.

Any of several insecticides can control tent caterpillars. Because insecticides are labeled for use on specific host plants, be sure to follow the directions on the product label. Apply insecticides in the early morning so that the spray is concentrated on the tents where the caterpillars congregate.

Plant-derived or naturally occurring insecticides include pyrethrins and insecticides made from plant oils. Like horticultural oils, plant oil products are contact insecticides and must be applied directly to the caterpillar tents or resting masses for control.

Spinosad is a low-toxicity, naturally derived product that provides excellent control of caterpillars while preserving most beneficial insects. Spinosad is a naturally derived fermentation product from a soil microorganism. It is one of the few natural insecticides that continues to provide control for 7 to 14 days after treatment.

Many longer lasting, synthetic products also can control tent caterpillars. These products provide faster, longer-lasting control than do most plant-derived insecticides. However, most of these products are toxic to beneficial insects as well as the pest caterpillars.

Pesticides that provide good tent caterpillar control include those containing permethrin, lambda-cyhalothrin, cyfluthrin, bifenthrin, fluvalinate, esfenvalerate, carbaryl, acephate or malathion.

Before purchasing or applying pesticides ALWAYS READ AND FOLLOW CAREFULLY THE INSTRUCTIONS ON THE CONTAINER LABEL. The regulations on insecticides are subject to change, and changes may have occurred since this information was obtained for release. The pesticide users are always responsible for the effects of pesticides on their own plants or household goods as well as problems caused by drift from their properties to neighbors’ properties or plants.