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FPL 17 - Forest Tent Caterpillar

The information accessed from this screen is based on the publication: Wood, C. S. 1992. Forest Tent Caterpillar. Forestry Canada, Forest Insect and Disease Survey, Forest Pest Leaflet No. 17 4p.



The forest tent caterpillar, Malacosoma disstria Hbn, is one of the major defoliators of deciduous trees in the interior of British Columbia. Outbreaks covering large areas of trembling aspen stands have occurred periodically since the 1920s, and were continuous in parts of the interior from 1967 to 1976 and in the 1980s and 1990s.

Historically, outbreaks of this insect have caused more concern for homeowners (Fig), city and town officials, and for parks and recreation staff than for foresters. Often, the rapid defoliation of host trees by millions of caterpillars (resulting in mid-summer starkness and replication of winter settings) occurs before questions are asked, and by then it is much too late to implement protective treatments.

In addition to the temporary loss of amenity values, congregations of large numbers of caterpillars around homes and in public places and caterpillars falling from trees can cause serious distress to people who dislike insects. Occasionally, in B. C. and elsewhere, large numbers of the caterpillars on the ground have been known to disrupt rail and highway traffic; their smeared remains may make transportation routes slippery and hazardous.

The extensive stands of trembling aspen in northeastern B. C. have been severely infested during the period 1989-1991. During 1990, infestations and defoliation occurred at more than 370 locations covering 206 000 ha. The outbreaks have spilled into urban centers (Prince George) and many smaller communities. Undoubtedly, as long as a food supply for this insect exists, it will be important to those concerned about amenity and property values. As forest management develops in these forests, specialists in planning, forest health, forest recreation, and wood fibre production will likely become concerned as well.


For more information, see the Forest Tent Caterpillar Forest Pest Leaflet in the Canadian Forest Service bookstore.