Tent caterpillars help more than hurt wildlife

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By Sylvia Brockner

If you are one of the many people who find tent caterpillars objectionable in your backyard, now is the time to control them.

I know they do little harm in our forests, but I find it difficult to be tolerant of them. Their favorite food is the new leaves of apple trees, so they were very common and considered destructive pests in the apple-growing sections of New York state where I grew up.

However, their second choice of food is the new spring leaves of the wild chokecherry, which is a native of this area and a source of food for many birds, small animals and even bears. I have a cluster of small chokecherries in my yard, and the fruit is so popular that it seldom is fully ripe before it is consumed by wildlife.

So, if you don’t want your chokecherries stunted by tent caterpillars, now is the time for action, and it doesn’t involve the use of any chemical sprays. The adult is a small brown fuzzy moth. As an adult, it laid eggs last summer on the twigs of chokecherries, apple and other host trees and shrubs in an oval mass.

Look over your shrubs before the leaves appear and see if you can locate such an egg mass. It will be the same color as the twigs but will be shiny, oval-shaped and usually placed near a fork on the stem.

It is shiny because the female moth covers the egg mass with a varnish-like substance, which seals the mass so the eggs don’t get wet during winter weather. When the first eggs hatch, the caterpillars are tiny little black things, which almost immediately spin a silk thread that they use to make a tent around the forked branches.

This is usually in May or early June, but the caterpillars grow rapidly and molt their skin five times before they are grown, and the nest tent must be enlarged to accommodate the growing family.

When I was a child, they were such a threat to apple trees that we used to have to find the egg masses and prune them out of the shrubs before they hatched. It was eventually discovered that by eliminating all of the tent caterpillars, the creatures that preyed on them declined as well. Eventually, it was considered better not to remove all of the egg masses but to let some of them hatch to supply their native predators with enough food to return and keep them under control.

Our cow pasture had been planted with hawthorns, as they were prickly enough with their long thorns that the cows didn’t mow them down and could have some summer shade. These small trees and shrubs were the home of many birds such as robins, catbirds, brown thrashers and others who paid for their easy life by eating tent caterpillars and by their fine choruses of song.

The birds’ nests were so common in the hawthorns or crabapples that we joked about their being able to have a breakfast in bed and that feeding a family was an easy job. The many birds did keep the tent caterpillars under control and out of the apple orchard.

After shedding their skin five times, the caterpillars are grown and spin themselves into a cocoon, which is thimble shaped. Each time they have shed their skin, they have changed color and have changed from black to blackish and yellow stripes and have a heavy coat of bristles, which are yellowish-tan.

The caterpillars leave the nest each morning to crawl out among the branches looking for new green leaves to eat. They lay down a silken thread as they go and use this as a trail marker to find their way back. Late each afternoon they return to the nest for protection overnight. When the larvae emerge from their cocoons, they have transformed into brown furry moths, and the cycle starts all over again.

A similar insect, which is of much more concern here, is the fall web worm. They build a much bigger web nest in the top of evergreen trees and consume all the growth within the nest, thus often destroying the leader of pines that continue the upward growth of the tree. This doesn’t usually kill the tree but often deforms the growth so the tree is less valuable as timber. Their nests don’t usually appear until late summer, thus the name fall web worm.

Bluebirds are coming

If bluebirds bring us happiness, the least we can do is to provide them happy homes. The Evergreen Naturalists Audubon Society will hold its annual nesting box sales March 13-14 from 9 a.m. to 3 p.m. at the Bergen Park King Soopers store and the Safeway stores in Evergreen and Conifer. The boxes are constructed by TENAS volunteers from select cedar to exacting standards. Proceeds go to TENAS projects on environmental education and habitat improvement. For more information, call Bud Weare at 303-679-8889.