Ask the Expert: What Are Those Caterpillars in My Trees?

There have been many calls from people on Long Island who are seeing “Gypsy Moth Caterpillars” out in large tents, and asking how bad the season will be. Fox Tree Service president Bart L. Fuscoa Certified Arborist and Registered Consulting Arborist—reveals that the pest is not what many of those people may think.

The tree pest that is being described is not the Gypsy Moth Caterpillar, but rather the Eastern Tent Caterpillar, Malacosoma americanum, which is also a pest native to North American trees.

The size, long hairs and shape are very similar, however the coloring is different.

The Gypsy Moth Caterpillars have red or reddish markings along with some darker spots, and although they will feed on almost any tree and other plants, they come out after the Eastern Tent Caterpillars are finished. They feed heavily on the White Oaks, which break bud later than the Red Oaks.

The Eastern Tent Caterpillar has all dark spots, often blue. They build their nests in and feed on wild cherry, apple and crabapple, but may be found on other plants as well. 

The nests, created from a silk-like material the caterpillars spin, are built in the crotches of limbs and can become quite large.

Life Cycle

The Eastern Tent Caterpillar adult deposits her eggs on the branches of her favorite tree, the branches almost always used are about the size of a pencil. The egg mass is very shiny and black, and form a circle around the branch about an inch long. On clear winter days, the eggs are easy to spot as they reflect the sunlight brilliantly. These egg masses can contain up to 400 eggs.

The caterpillars usually hatch about the same time that the foliage of their host trees start to break bud. On Long Island the caterpillar hatching is in March.

After hatching they spin a silken tent in a crotch of the tree. Multiple egg masses can create a single large tent. The tent provides protection from predators, rain and extreme heat. They like to feed during the cool hours of the morning.

The caterpillar pupates, forming a cocoon, and emerges a few weeks later as an adult.

Moths find each other and mate; the females begin to lay eggs on the small branches, starting the cycle over again. These eggs will hatch the following spring; there is only one generation of this pest per year.

Control

Mechanical:

Look for the egg masses prior to their hatching, when they can be easily removed by hand or small pruning shears from low branches. If you miss some, they will develop a nest, which can be removed by wiping it off. If removed during the warmer time of the day, this will eliminate the caterpillars that stay in the nest after the day warms. DO NOT burn the nests; this can cause damage to the tree.

Insecticides:
Bacillus thuringiensis var kurstaki , a biological insecticide, will work best when used on the young larvae. As the caterpillars get larger, a more conventional pesticide will be needed.

If you have a tall tree, and the eggs or tents cannot be reached, you may want to seek the help of a professional certified applicator.

It is already late in this pest’s development, so talk to an arborist and see if the nests contain live caterpillars, before a treatment program is initiated.

These photographs were taken this morning, May 8, 2012, by breaking open the nest it shows the insect is still active.

Have questions about caterpillars in the trees in your yard or looking for other tree-care information?  You can contact Fox Tree Service in Suffolk at  631-283-6700, and in Nassau at 516-921-7111, or visit online at foxtreeservice.com.  

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