Blueberry Spanworm (BSW)

Photo Credit: Cutler Lab

Blueberry Spanworm (Itame argillacearia) or BSW is one of the important defoliators (lepidopteran pests) of lowbush (syn. 'wild') blueberry and commonly found in north-eastern North America1. BSW larvae may feed on leaves, flower buds, blossoms, and vegetative shoots of blueberry plant.

The Larvae enter the buds making small entry holes and devour it completely from inside. In severe outbreaks, extensively damaged fields may show areas that appear burned, with only the twigs and stems of the plants remaining 2,3

BSW larva can be easily recognized by its “looping” walk. Young BSW larvae are about 1/8-inch long and dark gray to black with a series of white bands encircling the body. Fully grown larvae are about 3/4-inch long and yellowish-orange with rows of black spots that may appear like continuous black stripes running down the length of the body. Spanworm larvae are generally active on the plants in large numbers during night. During the day, the larvae will prefer to take shelter in the litter or inhabit base of the plants 1, 2, 3, 4.

Pupae, which are rarely seen, can be found in the leaf litter and are dark brown or black.

Adult BSW are delicate, light gray moths with a wingspan of about one-inch. They can be found in blueberry fields and in nearby weedy areas or wind breaks and will fly readily when disturbed. Eggs, generally pink to green in color, are laid on the leaves or on the leaf litter and will hatch only in the following crop season 1,2.


1. Ramanaidu, K. et al. (2011). Laboratory and field susceptibility of blueberry spanworm (Lepidoptera: Geometridae) to conventional and reduced-risk insecticides. Crop Protection 30: 1643-1648.

2. Crozier, L. (1995). Blueberry Spanworm Fact Sheet. Nova Scotia Department of Agriculture and Marketing.

3. Drummond, F. A., & Groden, E. (2000). Evaluation of entomopathogens for biological control of insect pests of lowbush (wild) blueberry. Technical bulletin 172. University of Maine cooperative extension. (http://www.umaine.edu/mafes/elec_pubs/techbulletins/tb172.pdf)

4. Agriculture and Agri-Food Canada (2011). Crop profile for lowbush blueberry in Canada, Ottawa, ON, Canada. Catalogue No. A118-10/31-2012E-PDF