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The eastern tent caterpillar, Malacosoma americanum, is a pest native to North America that can cause serious defoliation to deciduous trees in the family Rosaceae, in particular to Cherry (Prunus) and Apple (Malus).It is often mistaken for the Gypsy moth caterpillar as they emerge at similar times in the spring, and the fall webworm (which appears in late summer and fall). Eastern tent caterpillars can defoliate a tree but trees will usually recover from one or two years of damage. Successive years of high populations can cause stunted growth for host plants and may make them susceptible to disease.
The adult moth will lay 150-300 eggs that will overwinter in shiny, varnished-looking, black masses encircling a branch or limb. Eastern tent caterpillar egg masses do not encompass foliage as the fall webworm masses do. The egg masses are easily spotted especially during the winter months when trees are bare of foliage.
Whitney Cranshaw, Colorado State University, Bugwood.org
It is in March when the eggs hatch that their presence is easily seen. As the young hatch they spin their silken tent in the crotch of a branch. The newly emerged caterpillars will stay together, sometimes joining with the young from a nearby egg mass to form one large community.The caterpillars will emerge from their protective tent in the early morning, in the evening or even at night to feed. They will stay within their enclosure during the heat of the day, if it is raining or if it is too cold. Over the next 4-6 weeks they will feed on nearby foliage, increasing the size of the tent to accommodate their increasing size. The black caterpillar with a white stripe bordered by blue down its back will reach a length of 2 to 2 ½” at which point they will stop feeding and will leave the tent.
The larvae are frequently seen wandering across walkways, roads, buildings, and other plants as they look for protected places to spin a 1” long, whitish cocoon and pupate The reddish-brown adult moth will emerge 3 weeks later to mate and lay the eggs on small branches that will hatch the following spring. There is one generation per year and populations will fluctuate from year to year.
The Forest tent caterpillar, Malacosoma disstria, is a look-a-like to the Eastern tent caterpillar but it has white spots down the back instead of a stripe. It feeds on deciduous shade trees such as ash, aspen, birch, elm, oak, and sugar maple and flowering fruit trees such as cherry. It does not construct tents like other species in the Malacosoma genus, instead it will spin silken sheets where the larvae will congregate in groups. It will create a white cocoon in folds of leaves or another protected area in which to pupate, emerging 3 weeks later as the adult moth. It also has an overwintering egg mass similar to the Eastern tent moth. Control measures are similar to those below.
Image by Linda Spoerl
The Eastern tent caterpillar favors members of the Rosaceae family as its host plants. This family includes the genus Prunus which encompasses almond, apricot, cherry, crabapple, peach, plum, and quince, the genus Cotoneaster which includes hawthorn and rowans, and the genus Sorbus which contains service tree and mountain-ash.
Despite good cultural practices, pests and diseases at times may appear. Chemical control should be used only after all other methods have failed. READ THE LABEL on each pesticide container before each use. Apply as directed. Heed all warnings and precautions. Store pesticides in their original labeled containers out of reach of children, irresponsible people and pets, preferable under lock and key. Dispose of empty containers safely.
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Revised by UConn Home and Garden Education Center 2016.
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