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Hola Bagworms

Timothy J. Gibb, Ph.D.

Bagworms have recently become very serious pests throughout Indiana and are causing considerable panic by those caring for junipers, arborvitae and even other deciduous trees and shrubs. The mild winters of the last few years have not killed as many eggs as usual and are blamed for this increase in population numbers.

Bagworms live singly within a small spindle shaped bag that they carry with them as they feed. This bag is made from bits of foliage tied together with silken threads and offers protection from predators and parasites. Inside the bag is a worm or caterpillar (immature stage of a moth) that expands the bag up to two inches in length as it feeds and grows. When bagworms occur in large numbers, serious defoliation of the tree or shrub results.

This defoliation begins in the springtime but becomes very obvious by July or August. The best time to control these insects has passed (mid June), however, some control can still be achieved by using 'pyrethroid' insecticide applications or a new product called 'spinosad'. Both of these treatments have homeowner labels that mean that they can be purchased and used by the public without special licensing. Just follow the directions closely. There are no systemic treatments that can be added to the soil or the trunk of the tree that offer consistent bagworm control. One of the most certain methods of control is still the age-old technique of physically picking the bags off of the trees and destroying them. This technique offers the homeowner several distinct advantages. First, it is absolutely effective. There is no question about them returning to life and continuing their feeding. Secondly, it reduces the expense and potential for harm that using pesticides might pose to people and the environment. Thirdly, and sometimes most importantly, it allows for personal revenge against these ornamental plant enemies. There is something somehow satisfying to ones soul - in a sick sort of a way - to be able to actually drown the little buggers in a container filled with dish soap and personally watch their wriggling, writhing demise, especially after they have caused serious damage to ones property. Sort of like Arnold Schwarzenegger saying "Hasta la vista, bagworm".

A concentration of dish soap in a small container is usually sufficient for this but some have devised other methods of disposal that are even more devious and - dare I say - satisfying. I will not describe these methods here, but you can use your imagination. The bottom line is that when picking the bags off the tree or shrub, they must be disposed of. If dropped to the ground, they will simply climb right back on the plant again.

Click on the small image to view a larger image.

Bagworms Bagworms

Bagworms
(Photo by Peggy Sellers)

Bagworm on arbovitae Tree infested by bagworms
Bagworm on Arbovitae
(Photo by Peggy Sellers)
Bagworm Infested Arbovitae
(Photo by Peggy Sellers)
Bagworms
Bagworms
(Photo by Peggy Sellers)

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Last updated: 30 July 2002/tlm.
The Plant & Pest Diagnostic Laboratory at Purdue University.