Tent Caterpillars

     Early in May we begin to see many tiny, white tents of webbing in the crotches of cherry trees here in southeastern Pennsylvania.  Those tents are made by the larvae of a kind of small, brown moth; what we call tent caterpillars.  As those many sibling caterpillars grow, they daily add more silk to their nests, making those shelters ever bigger, too.  Each tent has an opening on one side and is peppered with small, dark droppings.      
     Tiny, black tent caterpillars hatch from eggs in a small, dark mass of eggs on the bark of cherry trees late in April and soon begin eating newly sprouting cherry leaves on the trees.  And the larvae immediately start creating their sheltering tents with their own silk they spin from spinnerets on their rear ends.  The growing larvae are hairy, but have lovely colors and designs.  They are mostly blue, black, white and orange.
     The caterpillars consume cherry leaves at dawn, mid-afternoon and after sunset.  They leave their tents to move out to where the leaves are, laying down paths of silk on the limbs and twigs that they will follow to get back to their shelters when full of foliage.  Older larvae feed only at night.
     Yellow-billed cuckoos and black-billed cuckoos are the only birds in North America that will regularly eat the hairy tent caterpillars.  Those cuckoos are the only birds that specialize in eating hairy caterpillars of many kinds.
     Mature tachnid flies and the adults of certain kinds of wasps lay eggs on tent caterpillars.  The larvae of those flies and wasps consume the moth larvae.       
     By the end of May the surviving members in each tent disperses, crawling across the ground to find a sheltered place in the soil to pupate.  Adult moths emerge from those cocoons about two weeks later.  Those moths are nocturnal, flying only at night in search of mates.  Mating and egg-laying occur on the day the moths emerge from their pupae. 
     Each female moth lays 200 to 300 fertile eggs in a single batch on a cherry tree.  She has to be a little forester to know which tree to use because the caterpillars only eat cherry, and apple, leaves.  In about three weeks, about the second week in July, fully formed larvae are in those eggs, but they remain dormant until the end of next April, when they hatch and begin another cycle.
     Tent caterpillars can cause damage to cherry tree and apple tree foliage, perhaps killing a tree or two.  But that is unusual.  For the most part, the tents of tent caterpillars are another unique and interesting part of late spring in this area.  The larvae of a little, brown moth are more intriguing than damaging.