We investigated the diets of insectivorous bats (Chiroptera: Vespertilionidae) in forests with high densities of western spruce budworm (Choristoneura occidentalis, Lepidoptera: Tortricidae), in southern interior British Columbia, Canada. Caterpillars as potential prey were more common and widespread than previously reported. Caterpillar consumption by bats was more frequent where C. occidentalis larvae were more abundant, suggesting that the caterpillars being eaten were C. occidentalis. The frequency of caterpillar consumption was similar for Myotis evotis, which gleans prey from vegetation, and for other bat species that forage primarily by aerial-hawking. We suggest that caterpillars hanging by silk threads were captured by bats that foraged aerially.