197-Blueberry Spanworm (Itame argillacearia (Packard))

Fact Sheet No. 197, UMaine Extension No. 2371

Prepared by Judith A. Collins, Assistant Scientist, and H. Y. Forsythe, Jr., Professor of Entomology, in cooperation with David Yarborough, Extension Blueberry Specialist, The University of Maine, Orono, ME 04469. November 1995.


Young caterpillar 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 are yellowish-orange with rows of black spots that may look like continuous black strips running the length of the body (Photo 1). Spanworm larvae often appear on plants in large numbers at night.   During the day, many larvae find shelter in the litter at the base of the plants.

An easily recognizable characteristic of this larva is its “looping” walk.  Pupae, which are rarely seen, are found in the litter and are dark brown or black.

spanworm growth stages header for photo gallery reads: actual size, egg, larva, pupa, adult

Adult spanworms are delicate, light gray moths.  They have a wingspan of about one-inch (Photo 2).  They are especially common in weedy areas or windbreaks and will fly readily when disturbed.

Life Cycle

The blueberry spanworm spends the winter as an egg in the litter near the base of blueberry plants.  Eggs may begin to hatch and larvae start feeding on developing buds as early as April and continue to feed on blueberry leaves, buds, and blossoms until late June or early July.  Fully grown larvae move into the litter, where they remain as pupae.  At this stage and time, they do not feed.  Moths begin to emerge in about two weeks.

Adults can first be seen in the field in early to mid-June.  Some moths may still be present until late July. Eggs laid by the moths do not hatch until the following spring.

Damage and Economic Importance

Infestations of blueberry spanworm may be confined to isolated areas or damage may be widespread.  Large numbers of spanworm larvae may completely defoliate areas in both crop and pruned fields. Early in the season, the larvae damage the berry crop by eating flower buds and blossoms. Later larvae chew out notches on developing leaves (Photo 3). Crop fields may be dotted with areas that appear burned (Photo 4).

The first sign of a severe infestation in a pruned field is an area devoid of or with slower developing plants; look for signs of feeding on developing shoots at ground level or below the soil surface.

Pest Management

The blueberry spanworm can be controlled with an appropriate pesticide.  For additional information on monitoring and control, refer to Wild Blueberry Fact Sheets Nos. 204 and 209, or contact the lowbush blueberry specialist, University of Maine Cooperative Extension, 1.800-.897.0757 (toll-free in Maine) or 207.581.2923.

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 1995

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