Northern tent caterpillar
Latin name: Malacosoma californicum pluviale (Dyar)
French name: Livrée du nord
British Columbia, Newfoundland, Ontario, QuebecThe northern tent caterpillar is a native North American insect. It occurs throughout the southern half of British Columbia, and its range extends as far east as Quebec. In the United States, it is primarily found west of the Cascade Mountains, through Washington as far as southern Oregon. Populations are known in northern Idaho, western Montana and several northeastern states also.
Damage, symptoms and biologyDefoliation intensifies as larvae mature, and trees often become stripped of foliage by mid-June or early July. Significant damage to the trees 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 in the second crop. Trees weakened by feeding damage are more susceptible to secondary effects such as infection by fungi and the environmental stresses of drought and frost.
Larva: Larvae are about 3 mm long when newly hatched, and are uniformly dark with conspicuous whitish hairs. Fully grown, they are 45-55 mm long, have a dark brown base colour overlain with 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 further pair of blue dots lower down on the sides. Beneath these patterns, and low on the sides of the body, runs a single orange stripe. The above description fits an average specimen, though the patterns are highly variable.
Pupa: A dark reddish-brown pupa 15-20 mm in length rests inside a pale oval silken cocoon that is dusted with a yellowish powder.
Adult: Moths are stout bodied with a wingspan of 25-37 mm. Colours range from pale yellow to dark reddish brown. A single dark line radiates at right angles to the body, bisecting the forewings. Two lighter lines running parallel to the outer edge of the forewings further divide them into three segments of equal width.
Eggs: Egg bands averaging about 15 mm in width are laid, partially encircling small branches and twigs. Between 150 and 250 eggs are laid within a foamy silver-grey matrix called spumaline that protects them and bonds them to the branch.
The northern tent caterpillar has a 1-year life cycle. First-instar larvae emerge in the spring between mid-April and early June, having passed the winter fully formed within the eggs. Larval emergence is timed to coincide with budbreak on the host trees. Young larvae feed gregariously on the new foliage, and weave a large silken tent in the crotch of a branch. Larvae from several egg masses may construct a single tent. Tents are enlarged as the larvae grow, providing protection from predators during resting and molting phases and shelter in periods of bad weather. Larvae pass through five or six instars during the 6-week feeding period. In the final instar they lose the gregarious habit and disperse in search of a suitable pupation site. Pupation occurs inside a tightly woven cocoon attached to a tree, shrub or other sheltered location. Moths emerge 2 to 3 weeks later and mate. Females subsequently lay their eggs on the branches of a suitable host.
Other informationThe northern tent caterpillar is one of six recognized subspecies of the western tent caterpillar, Malacosoma californicum, which ranges from southern Oregon through southern California. A related species, the forest tent caterpillar, Malacosoma disstria, is a major defoliator of trembling aspen in the British Columbia interior.
Canadian Forest Service Publications
Diet and feeding behaviour
- Phyllophagous: Feeds on the leaves of plants.
- Webworm: Spins a silk shelter in which to hide or feed.
Apples, balsam fir, balsam poplar, dwarf birch, Garry oak, grand fir, hawthorns, lodgepole pine, Lombardy poplar, mountain alder, northern red ash, Rocky Mountain Douglas-fir, Saskatoon, Sitka alder, water birch, western hemlock, western redcedar, white birch
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