The forest tent caterpillar has caused repeated serious defoliation of
hardwood forests throughout North America. Aspen, water tupelo, hard
maple, gums, and oaks are preferred hosts but this insect will feed on a
variety of other broadleaf trees.
[Illustration: Forest tent caterpillar larvae.]
The shiny black egg masses encircling the twigs of host trees can be
seen during winter months. Small black, hairy larvae hatch out just as
the leaves are beginning to unfold. They do not construct a tent, but
make a silken mat on the larger branches or trunk of the tree on which
they rest between feeding periods. When full grown, the larvae are about
two inches long, brownish-black with distinctive white, keyhole-shaped
spots down the middle of the back, and blue lines along the sides. Just
before pupating, the larvae spin a whitish silk cocoon on the bark or
leaf of the host. In about ten days the light brown moths emerge, mate,
and the females begin laying their eggs.
Parasitic flies are one of the more important agents which normally keep
this insect under control. Outbreaks occur with some regularity,
however, and chemicals may be required to prevent defoliation.
[Illustration: Colony of third instar larvae.]