Native to North America, the eastern tent caterpillar (Malacosoma americanum) is a defoliating caterpillar that has been reported as early as 1646.  Up until the 1970’s and 1980’s the eastern tent caterpillar had been considered one of the most common and destructive defoliating insects in the eastern United States. 

In late spring and early summer, the eastern tent caterpillar creates an unsightly nest or tent in the crotch of branches.  The feeding of the larvae in late spring and early summer strips the foliage from trees.  Complete defoliation can occur when caterpillar populations are high.  The larvae can become messy as they crawl on sidewalks, patios, and driveways where they become squashed.

Susceptible Hosts
Common hosts include Prunus species such as cherry, plum, and peach, as well as flowering crabapple (Malus), hawthorn (Craetagus), and pear (Pyrus).  Other hosts include maple (Acer), ash (Fraxinus), birch (Betula), oak (Quercus), willow (Salix), and poplar (Populus).

Pest
Malacosoma americanum

Symptoms
* Stripping of the foliage in late spring and early summer.

Signs
* Mature caterpillars are usually black with a white stripe down the back.  A line of blue spots run between yellow lines down the sides of the caterpillars.
* Adult moths are reddish brown with two whitish stripes running across each forewing.
* A silky nest or tent in the crotch of branches.

Life Cycle
* Eggs hatch in the spring at about the same time as leaf emergence on cherry.  
* Young larvae begin building their silken tents in a major branch fork or crotch.
* The larvae feed for a period of six to eight weeks before migrating to a protected site to pupate.
* The pupal stage lasts for about three weeks.
* Adult moths emerge in early summer.  Females deposit their egg masses around small twigs where they over winter.
* One generation per year.

Distinguish from Look-alikes
* Many caterpillar species infest certain hosts making knowledge of susceptible species and proper identification of the host plant helpful in diagnosis.  In addition timing of symptoms and particular marking characteristics are key distinctions between caterpillars.
* Eastern tent caterpillar can be distinguished easily from its black color with a white stripe down the back, and the line of blue spots running longitudinally between yellow lines down the sides of the caterpillars.
* Fall webworms form tent-like nests at the branch terminals rather than nests in crotch of branches.
* Fall webworm is active in summer and early fall rather than the spring.
* Forest tent caterpillars form silken mats rather than tent-like nests.
* Gypsy moth is the only tussock (furry) caterpillar with five pairs of blue spots and six pairs of red spots in rows across its back.

Distribution
The eastern tent caterpillar is a common pest east of the Rocky Mountains.

Feeding from Eastern Tent Caterpillar larvae in late spring and early summer can completely defoliate foliage from trees.  Healthy trees can tolerate a single defoliation event, however, multiple defoliation events can cause dieback and when combined with abiotic stress events. 

The eastern tent caterpillar is easy to control if treatment applications are timed correctly in the spring of the year.

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