Southwestern Tent Caterpillar

Malacosoma incurvum

adult tent caterpillar moth, Malacosoma incurvum, photo © by Mike Plagens

silken tent constructed by caterpillars of Malacosoma incurvum photo © by Mike Plagens

Southwestern Tent Caterpilars were found in their tents on chokecherry growing along Devil's Canyon, Gila Co., Arizona, USA. May 2010. The adult, in top photo, emerged in early June. 2009.

By mid to late spring the large webbed tents of tent caterpillars begin appearing on trees of willow, cottonwood and in this case, chokecherry within and near sycamore woodland galleries. Occasionally the populations can grow so large that many trees are completely defoliated. Most years, however, the tents will be found with an incidence of one or two per tree. Normally caterpillar numbers are held in check by a array of predators - some birds, cuckoos for example, are able to penetrate the tents to get the worms. Predation also happens as smaller larva of tent caterpillar parasitic wasps and flies get into the caterpillars. The caterpillars emerge from the tents at night to feed and to expand the tent as necessary so that all can shelter within during the day when birds and parasites are most active.

In general, introducing pesticides to control these caterpillars is likely to make the problem worse because the pesticides kill off the natural predators. Trees that are defoliated quickly regrow a new set of leaves and suffer no long-term injury so long as heavy defoliation does not occur year after year.

Lasiocampidae -- Tent Caterpillar Family

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Arizona Naturalist
Sycamore Canyons
Invertebrates in Arizona's Sycamore Canyons


Copyright Michael J. Plagens, 1999-2010