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Prairie Tent Caterpillar

Malacosoma californicum lutescens


Choke cherry, rose, and cotoneaster

Appearance and Life Cycle

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Prairie tent caterpillar. Photo credit : Terry Thormin,

Larvae emerge from eggs in the spring, just as the leaves begin to appear. The larvae have blueish-grey sides, and reddish-orange backs that are interrupted with a white stripe down the center. By early to mid-July the larvae are full grown, ranging from 40 to 50 millimetres (mm) in length. Moths emerge in early August, depositing egg masses containing up to 500 eggs each. The egg masses are deposited on twigs and branches and covered with a greyish foam-like substance. The Prairie tent caterpillar completes one generation per year.


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Larvae on the outside of their web. Photo credit: vermilion-river. com

Almost immediately after the larvae emerge, they construct tent-like webs in the branches. Caterpillars feed on foliage outside the tent, but return to the nest during adverse weather conditions. As the larvae develop, the tents are enlarged until they are unsightly masses of webbing containing excrement, casted larvae skins and larvae. Defoliation is usually confined to the odd branch, but there have been outbreaks where trees have been completely defoliated. Severely-infested trees may be temporarily disfigured and unsightly, but will not be permanently damaged.


Prairie tent caterpillar damage can be reduced by picking off and destroying the egg masses on trees in late fall or winter when they are easily seen. Caterpillar populations can also be reduced by removing and destroying tents on cool days when most of the larvae are within the nest. Chemical control of the pest can be achieved using acephate, Bacillus thuringiensis, carbaryl, deltamethrin, or malathion.

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