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Eastern Tent Caterpillar (Malacosoma americanum)
Often confused with the exotic gypsy moth and the fall webworm, the eastern tent caterpillar (Malacosoma americanum) is a native North American botanical pest found commonly on wild cherry, apple, hawthorn, plum, and maple trees. As the larval stage of a reddish-brown moth, periodic outbreaks of this nesting herbivore can cause serious tree defoliation, weakening but usually not killing the hosts.
In the spring, the larvae build silken tents in the crotches of the host trees. The caterpillars soon leave their nests to feed on young leaves and return daily after feeding or during rain. As the moth larvae grow, the bag or nest enlarges as well. A fully grown caterpillar before pupation reaches about 2 inches in length, is typically black with a white dorsal stripe, and is covered with fine, light brown hairs.
Tent caterpillars can overwinter in egg masses of 150 to 400 eggs that appear as shiny brown bands around the twigs of potential host trees. The tents protect the resting caterpillars from predators such as birds and from temperature extremes. The individual shown in this micrograph was collected in Tallahassee, Florida where winter and early spring temperatures can dip below freezing, and late spring temperatures, under strong sun, can exceed 95 degrees Fahrenheit. After about four weeks, the caterpillars pupate within a spun cocoon of closely woven white or yellow silk that is about 1 inch long. Three weeks later the adult moth emerges, mates, and lays her eggs for next year's generation.
The prevention of the denuding of ornamental and fruit trees can be achieved by manually destroying the tents with a stick or pole, exposing the caterpillars to predators such as blue jays and mockingbirds. Alternatively, with close examination in the early spring, egg masses can be located and destroyed before hatching. For most people, the Eastern tent caterpillars are more of a visual nuisance than a real economic threat. At the time of pupation, the larvae migrate to protected places and are highly visible on other types of plants, walkways, and storage buildings. Insects that are crushed on driveways, sidewalks, and patios can create quite a mess, but certainly delight insectivorous birds and other predators. In general, insecticides are not effective on mature Eastern tent caterpillar larvae.
Cynthia D. Kelly, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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