The Tent Makers

(This column was published in the June 19, 1995 Buffalo News.)

   The population of eastern tent caterpillars has fluctuated in approximately 
ten year cycles ever since these insects were first encountered by American 
colonists in 1646. This year they are at or near a population peak.

   Visit the countryside around Buffalo and you will soon find foot long 
grayish webs or "tents" in the crotches of fruit trees, usually apples or wild 
cherries. Look closely and you'll see dozens of fuzzy black caterpillars 
crawling about these nests or feeding on nearby leaves. Still closer 
examination will disclose silken trails leading out from the web to each 
individual caterpillar for these are the Hanzels and Gretels of the insect 
world.

   Like us this tiny insect spends nine months waiting to be born, but unlike 
us it then has only three months to live. From late summer to the following 
May hundreds of tiny eggs are encased in a small varnished-brown capsule that 
encircles a fruit tree twig. Then on a warm spring day tiny caterpillars eat 
their way out through egg and shell casing. Some begin web weaving immediately 
while others feed on buds and early leaves along the branch on which they 
emerged.

   For the next four to six weeks the caterpillars continue to feed, to 
enlarge their tent and to grow. They molt five times, befouling their home 
with discarded skins and excrement.

   Suddenly at this time of year their life-style changes. Having defoliated 
their home tree, they desert their tent, drop to the ground and seek new food 
sources. Their diet is no longer restricted to fruit trees: they stuff 
themselves on maples, birches, poplars and willows as well for these are their 
last meals.

   At this stage they often cross roads in search of foliage. Once in Canada I 
came upon a quarter mile of highway covered with a caterpillar hoard. A car 
had slid off the road on the slime of their crushed bodies and police were 
slowing cars to prevent further accidents.

   Within a few days surviving caterpillars weave a cocoon flattened against a 
tree trunk or building wall. They must fold themselves into this small web to 
pupate. After a three week metamorphosis a small tan moth emerges. With no 
mouth parts with which to feed, the only functions of its brief life are to 
mate and produce eggs.

   As a youngster a favorite task was burning caterpillar tents with a 
gasoline soaked rag on the end of a stick. Many still use that method to 
destroy the filthy nests, but care must be taken not to injure the tree or 
yourself in the process. Fruit growers prefer pesticides including the 
biological control, Bt.

   But my lifelong distaste for these insects was compromised recently when I 
read one of the finest nature books ever written, Vincent Dethier's "The World 
of the Tent-Makers." Dethier's elegant prose elicits empathy for this tiny 
forager.

   In particular, Dethier provides a litany of the predators, parasites and 
pathogens of this almost defenseless caterpillar. We are far from their only 
enemy. Ants drag them off to their subterranean caverns. Shield bugs follow 
caterpillar threads to the tent, there to suck each one "dry as an empty wine 
skin." Ichneumon wasps dash in to pierce caterpillar bodies and deposit eggs. 
The eggs hatch and the resulting parasites slowly eat their hosts: from 
caterpillar cocoons will emerge, not moths, but wasps. Fly grubs burrow into 
the caterpillars. Invisible viruses destroy whole colonies. Cuckoos eat the 
larvae in summer, chickadees and woodpeckers the eggs in winter.

   Despite all this, the species survives to continue its sylvan depredations. 
And this year tent caterpillars are doing far too well.