EPOW - Ecology Picture of the Week

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Caterpillars in a Tent

Credit & Copyright: Dr. Bruce G. Marcot

Explanation:  What's long and squirmy and lives in a tent?  OK, it's a tent caterpillar.  That was too easy.   This photo shows the larvae of the western tent caterpillar, Malacosoma californicum, taken in native grasslands of eastern Oregon.  The larvae in the photo have not yet reached mature size and coloration.  They have made their nest in the twigs of, and are feeding on, a bitterbrush (Purshia tridentata).   Western tent caterpillars are considered common forest pests.  Their springtime tents of white silk dot forest, fruit, and shade trees.  When abundant -- outbreaks occur every ten years or so -- the larvae may strip the foliage over wide areas and disperse in great numbers over the ground.  Humans then worry about their appetites and controlling their numbers.  Eventually, though, native predators and other organisms reduce their numbers -- such as the parasitic fly Sarcophaga aldrichi -- until the cycle starts again. The silk tent affords them protection and insulation during resting periods between feeding forays.  When mature, the tent caterpillar transforms into a moth that has no functional mouth parts and survives on what it ate as a larva.      Acknowledgment:  Thanks to Beth Willhite, entomologist, USDA Forest Service, Portland Oregon, for confirming the identification.    Information:          Lens, B. J., and C. Roland. 2000. Spatial analysis of large-scale patterns of forest tent caterpillar outbreaks. Ecoscience 7:410-422.        Miller, Jeff. 1995.  Caterpillars of Pacific Northwest forests and woodlands.  USDA Forest Service FHM-NC-06-95.