Don't worry (too much) about those tent caterpillars

Fri, 06/12/2015 - 9:30am

At the risk of starting what may be the great caterpillar controversy of 2015, I will say, simply, do not worry too much about the tent caterpillars that are currently appearing in many locations throughout the island. 

The presence of the caterpillars’ tents in trees seems to elicit an automatic response of horror, along with the need to do something, and so many people have asked me about them. To that end, I have spent some time researching the subject. Call it: “I read this so you don’t have to.”

There are three types of tent caterpillars in the Northeast region: forest tent caterpillars (Malacosoma disstria), the eastern tent caterpillar (Malacosoma americanum) and gypsy moth caterpillars (Lymantria dispar). The forest and eastern tent caterpillars are native to the region, while the gypsy moth is from France and has become naturalized in the United States. It is this latter type that seems to be dreaded the most.

The eastern tent caterpillar, like many insects, prefers specific types of trees to lay its eggs in. They particularly favor trees in the genus Prunus, which includes cherries and plums. They also like apple, crabapples, and other fruit trees, maples, birches, oaks and poplar. (This list is in no way exhaustive.)

The gypsy moth caterpillar prefers oaks over other trees, according to the “Caterpillar Comparison Chart” found on the website of the New York State Department of Environmental Conservation, but: “When populations are dense, larvae will feed on almost any tree and shrub.”

These caterpillars are around every year, with what appears to be an “infestation” only occurring every ten to twelve years or so. According to Douglas W. Tallamy, author of “Bringing Nature Home: How you can sustain wildlife with native plants,” and Professor and Chair of the Department of Entomology and Wildlife Ecology at the University of Delaware: “Eastern tent caterpillar is one of the main foodstuffs of both the yellow- and black-billed cuckoos, and tent caterpillar adults are eaten by many bird species, as well as by bats.” (pg. 161). 

My initial guess was that this year’s breakout was the eastern tent caterpillar. The nests are indeed appearing in the fruit trees — cherries, apples and the peach tree in my own yard, in beach plums along Corn Neck Road, and “all over the west side” according to many. My faith that these weren’t the dreaded gypsy moth was strengthened one day, when I watched a cuckoo in the peach tree. It spent quite a bit of time there, not at all bothered by my close presence while doing some yard work.

And then, just a few days ago, my guess was confirmed. Crawling up the side of the house was a caterpillar. I peered at it to observe the dots on it. Sure enough, they were all black and blue. If some of them had been red, it would have been a gypsy. (Disclaimer: just because the ones in my yard are the eastern ones, does not mean I am guaranteeing that the ones in other people’s yards are the same.)

At any rate, the adult ETC moths lay their eggs in the forks of tree branches. When the larvae emerge in the spring, they congregate together in the silken tents that protect them from predators by day, and come out to feed at night on the newly emerging foliage on the trees. The tents also protect the caterpillars from extreme weather and rain. 

When the larvae are fully grown, they will go out on their own to find a place to pupate, i.e. form a cocoon. The eastern tent caterpillar makes a white silk cocoon whereas the gypsy moth caterpillar forms a hard brown case.

Will they kill the tree? Most likely they will not, per the NYS DEC. Most affected trees will send out new leaves in July, and healthy trees can withstand two to three years of defoliation. However, if a tree is weak or otherwise ‘compromised,’ there may be death resulting. 

Does this mean you should spray? No. Spraying a tree with pesticides targets the entire tree and therefore all the many species of insects that may live there that you don’t see. In turn, birds that may eat the sprayed insects may themselves be poisoned. 

If the tents really bother you there are a couple of more environmentally correct solutions. One is to remove the tent from the tree and dip it into a detergent solution. Another solution I have seen offered up on social networking is to spray the tent with vegetable oil. One I particularly was intrigued with was the “poke it with a stick,” method, thereby releasing the larvae to be eaten by the birds. (You could find a little boy that likes to bash things and put him to work.)

This all seems to be a lot of work at a time of year when we all have plenty else to do. Besides, when the biological purpose of the tent is over, the “problem” will most likely resolve itself. And the cuckoos will be very well fed.