Bruce Spanworm

Fruit trees, native trees and shrubs including willow, poplar, maple and alder.

Buds - Large areas chewed from buds, petals and flower parts.
Leaves - Large areas chewed from leaves before bloom; severe infestations can almost defoliate trees.
Fruit - Holes in small fruit resulting in small russeted scars in mature fruit.

Larva - Yellowish-green to dark green with light to dark brown head; larger larva with cream to white lateral stripes and moves with looping motion.
Adult - Wingless female; male moth with thin, semitransparent wings banded with brown and gray.
span worm damage
Life History
Bruce Spanworm overwinters as eggs laid singly on twigs. The eggs hatch near the green tip stage of apple. Most larvae mature and drop to the ground by petal-fall. Larvae remain in the soil until pupation in the fall. Adults appear in October and November. Wingless females crawl up the tree, mate and lay overwintering eggs.

Examine fruit bud and blossom clusters for larvae and feeding damage. Limb taps can also detect larvae.


There are many natural enemies that affect Bruce spanworm populations. It is thought that parasites are important in controlling populations between outbreak, though they seem ineffective in regulating populations once an outbreak has begun. For the most recent information on insecticides available for control of this pest, call Agriculture and Agri-Food Canada's Plant Industry Directorate in Ottawa (toll-free) at 1-800-267-6315.