Here are simple, least-toxic methods to manage tent caterpillars and web worms.
Manual and Mechanical Controls
One of the best methods to control an infestation is to collect and destroy egg masses and larvae in branches and trunk.1 The larvae can be killed by probing the hole with a long, flexible wire.2 You can also scrape the nest onto the ground or into soapy water (make sure to wear gloves!).3 The best time to remove and destroy larvae and their nests is evening and early morning because the caterpillars will gather into their nests at night.4
Another non-chemical method is the use of nematodes, which are insect-eating worms. “Create a mixture of nematodes and water and place directly in the hole. The most effective method is soaking cotton strips in the solution and using tweezers to place as deeply in the hole as possible.”2
Bacillus thuringiensis (Bt) is often recommended for controlling caterpillar infestations and other insects. Bt is a biological pesticide that is naturally occurring at low levels in soil. A variety of Bt, Bacillus thuringiensis var. kurstaki (Btk), has been found to survive in the upper respiratory tracts of humans; however, there is no evidence of Btk-related illnesses. Therefore, NCAP maintains the precautionary principle that there is not sufficient evidence of Bt and Btk’s safety to humans to merit exposing human populations to it.5
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- U.S. Forest Service, Rocky Mountain Region. “Forest Tent Caterpillar.” 2011. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5343832.pdf
- Beyond Pesticides. “Least-toxic Control of Tree-Boring Caterpillars.” https://www.beyondpesticides.org/assets/media/documents/alternatives/factsheets/TREE%20BORING%20CATERPILLAR%20CONTROL.pdf
- Shetlar, David J. “Eastern and Forest Tent Caterpillars and Their Control.” Ohio State University Extension Fact Sheet.
- WSU Extension. “Biology and Control of Tent Caterpillar.” Gardening in Western Washington.
- Northwest Center for Alternatives to Pesticides. “Bacillus Thuringiensis (B.t.)” Journal of Pesticide Reform Vol. 14, No. 3: 1994. https://assets.nationbuilder.com/ncap/pages/26/attachments/original/1428423315/bacillus.pdf?1428423315