American Tent Caterpillars

     Around the middle of April every year in southeastern Pennsylvania, we see small, white "tents"
of webbing in crotches of wild cherry trees along woodland edges and rural roads.  Those silky-looking constructions are the works of newly-hatched American tent caterpillars.
     Each protective tent is made by scores of sibling caterpillars that hatched from a cluster of dark eggs laid around a twig of a cherry tree by a single female moth the summer before.  Moths of this kind are small, hairy and brown, with an average wingspan of one and a quarter inches.  The most obvious parts of this kind of moth is the dwellings the caterpillar siblings make with webbing they exude from their bodies, and the larvae themselves that get up to two inches long and are hairy with black and yellow stripes down their bodies and blue speckles.   
     American tent caterpillars are widespread in eastern North America, wherever cherry, apple and pear trees grow.  The larvae of each communal structure emerge from it at intervals each day in April and May to consume the leaves of the fruit trees they live on, which is cherry trees for the most part. Each larvae lays down a web of silk on the twigs it travels on so it can find its way back to its sheltering nest when it is finished eating.  And as they eat and grow, they add threads to their dwelling, which becomes larger and larger in just a few weeks.
     Two species of American cuckoos, the yellow-billed and black-billed, specialize in eating hairy moth larvae, including tent caterpillars.  Both these kinds of cuckoos are about the size of blue jays and have long, curved beaks that use to reach into caterpillar tents to pull out and consume the larvae.  These cuckoos seem a bit sluggish, but they don't have to be quick to catch caterpillars.
     Toward the end of May, each tent caterpillar is as large as it will get.  All of them stop eating leaves and crawl away from their tent homes and across the leaf-covered ground to sheltered places under logs, bark or rocks where they can pupate in relative safety.  A couple of weeks later each one emerges from its cocoon as a small, inconspicuous moth that looks for a mate, lays eggs and dies.  But the next generation of tent caterpillars is in an egg mass attached to a cherry twig.
     Tent caterpillar homes are conspicuous in cherry trees at this time.  One can watch the caterpillars' interesting comings and goings from their shelters until they leave their tents to hide away and pupate toward the end of May.