Northern tent caterpillar, Malacosoma californicum pluviale
 

Fig. 328   Adult northern tent caterpillar.	Fig. 329  Northern tent caterpillar larva	Fig. 330  Northern tent caterpillar larvae on tent.

Distribution:  Southern half of B.C. 

TREE SPECIES ATTACKED: A wide range of broadleaf hosts are susceptible, including red alder, black cottonwood, paper birch, balsam poplar, hybrid poplar and trembling aspen. Willow and fruit trees are also attacked.

WHAT TO LOOK FOR: Conspicuous silken tents on branches and stems, from which caterpillars feed gregariously on the foliage.

INSECT DESCRIPTION & DAMAGE SYMPTOMS: Fully grown larvae are 4.5 to 5.5 cm long. They have a dark brown body, which is not conspicuous because of prominent markings that can vary highly between individuals. An average specimen has a series of narrow, light blue-grey elliptical patches along the midline of the back, corresponding to each body segment. Each of these is bracketed by a pair of orange patches, and a pair of blue dots lower down on the sides. A single orange stripe runs beneath these patterns, low on the sides of the body. Adult moths range in colour from pale yellow to dark reddish-brown, and have a wingspan of 2.5 to 3.7 cm. When open, the wings have a single dark line that radiates at right angles to the body, bisecting the forewing. Two lighter lines running parallel to the outer edge of the forewings divide them into three segments. Eggs hatch in the spring at the time of budbreak. Young larvae are gregarious and spin a large silken tent in the crotch of a branch from which they feed on new foliage. Tents are enlarged and defoliation intensifies as the larvae mature. Trees often become stripped of foliage by mid-June or early July. Just prior to pupation, larvae wander away from the host tree, and can be seen crawling in all directions in search of a suitable pupation site.

DAMAGE: Significant damage occurs only after prolonged severe infestations, and is limited primarily to loss of growth potential and some branch dieback. Defoliated trees usually refoliate in mid-summer, but leaves are often smaller. Trees weakened by repeated defoliation are more susceptible to secondary effects such as infection by fungi, drought, and frost. 

SIMILAR DAMAGE: Northern tent caterpillar tents are found on branches and stems, with larvae occurring on the surface of the tents. Fall webworm larvae, by contrast, are found inside nests which enclose more foliage than northern tent caterpillar tents.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated March 04, 2002