Forest Pests: Insects, Diseases & Other Damage Agents

Bagworms (Family Psychidae)

Maier, C.T., C.R. Lemmon, J.M. Fengler, D.F. Schweitzer, and R.C. Reardon. 2004. Caterpillars on the Foliage of Conifers in the Northeastern United States. FHTET-2004-1. Morgantown, WV: USDA Forest Service, Forest Health Technology Enterprise Team; 151 p.

The caterpillars in this small, primitive family live in silken cases into which they incorporate parts of leaves, twigs, or debris that can make them less conspicuous. These cases, which are responsible for the common name of the family, may reach a length of 50 mm. Each case has two openings, one at the top and another at the bottom. The caterpillars extend the front end of their body through the top hole to eat lichens or the foliage of woody trees and shrubs. They eject frass (pellet-like excrement) through the bottom opening. In the United States, three species of bagworms can have an economic impact, with the one described in this manual being the lone defoliator of conifers.

Some of the bagworms can be identified by the shape of their cases or by the material used to construct them. All of the caterpillars have the spiracle on T1 fused to the prothoracic shield. Bagworms typically have a single pair of prolegs on A3 to A6 and A10; the crochets are arranged in a characteristic pattern.

In most species, the males and the females are medium-sized moths that differ in appearance. The females typically are larva-like, with their eyes, antennae, mouthparts, wings, and legs greatly reduced or absent. They spend their entire life in the case. Females attract day-flying males with a sexual scent, mate, and then lay eggs in their case. Many of the males have drab coloration and a large scaleless area on their wings. Neither sex is known to feed.

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