Bagworms on Spruce and Pine: Identification and Control

Those "Pine Cones" Are Actually Insect Cases

The spindle-shaped, foliage-covered bags hanging from your blue spruce are bagworms (Thyridopteryx ephemeraeformis), not pine cones. Each bag houses a caterpillar that feeds on needles, causing defoliation and "flagged" dead tips.

Life Cycle & Hosts

Larvae build and carry their silk bags, enlarging them as they grow. They favor arborvitae and red cedar but attack many conifers (spruce, pine, juniper, cypress) and deciduous trees (oak, maple, elm, apple). One generation per year; eggs overwinter in bags.

Control Options

Mechanical (Small Trees)

Hand-pick and destroy bags in fall/winter before eggs hatch. Cut the silk band to avoid girdling branches.

Biological (Early Summer)

Apply Bacillus thuringiensis (Bt) in late June after all eggs hatch. Bt only works on young larvae that ingest it.

Chemical (Late Spring/Early Summer)

Stomach insecticides (acephate, bifenthrin, carbaryl, spinosad) must thoroughly cover foliage so larvae consume treated needles. Spray when bags are small (June). Later sprays are less effective.

Key Timing

Scout in late May/early June. Treat when bags are ½–1 inch long. Once bags reach 2 inches, control is difficult.