2017-06-01 / Nature

The Cursed Shipment of Silk

By Charles Avenengo


A female American goldfinch at Sachuest Point perches on a tree with a nest of gypsy moth caterpillars. (Photo by Carmen Rugel) A female American goldfinch at Sachuest Point perches on a tree with a nest of gypsy moth caterpillars. (Photo by Carmen Rugel) The details have been obscured over time, but around 1869, a square-rigger pulled out of a French harbor, bound for the New World. In addition to being laden with the usual items of commerce, this vessel had in its cargo hold the eggs of a moth that would ultimately affect millions of trees annually in the United States, including over 200,000 that were defoliated last summer in Rhode Island.

In those days, the sail westward across the Atlantic took at least two months, and this cargo of gypsy moth eggs had to be kept alive throughout the voyage until their safe unloading in Boston harbor. The recipient of the eggs was a recently immigrated Frenchman, Etienne Trouvelot. An amateur entomologist, Trouvelot transported his shipment from the docks to his house in Medford, just northwest of Boston. He cultivated the eggs and eventually had one million in his backyard. His plan was to use the silk from his imports to create an industry in North America that could compete with that of the more weather-delicate Chinese silkworm.

Naturally, the scheme failed. No silk was ever produced and the moths inevitably escaped.

Ten years later, having lost interest in entomology, Trouvelot had become an astronomer and was living in Washington D.C. Meanwhile, Medford had become infested with his legacy of gypsy moths. Over the next 150 years, the infestation would spread west to Minnesota and south to North Carolina, defoliating millions of trees along the way.

As it turns out, gypsy moths are not the only caterpillars leaving local forests bare. In addition to the European invasive, there are currently at least three other moth species hard at work, now chomping on local leaves.

Last week, Newport experienced a major outbreak of forest tent caterpillars, which is a native moth species. Massive amounts ballooned into Newport on silken threads, where they have feasted and denuded oaks, apples and other trees. The moths spun down in such numbers from the oaks at Trinity Church that more than 400 caterpillars were counted crawling around the southern face of the church. An additional 200 were on the church’s adjacent Honyman Hall. Other local areas, like Aquidneck Park, were also infected by the outbreak. “To some degree, the sky is falling. We are nervous,” said Newport Tree Warden Scott Wheeler. “Up until now we’ve been in better shape than the rest of Rhode Island. Newport has escaped the worst of it. This is something new.”

Wheeler said that the scale of the outbreak of forest tent caterpillars is a first. Newport has seen outbreaks by other species like honey locust leafhoppers and of course, a massive defoliation last year in Portsmouth by gypsy moths. But this is the first major assault in our area by this species.

“We have forest tent caterpillars every year. They move around. Last year the outbreak was in Richmond, Charlestown, Coventry and Exeter,” said Dr. Heather Faubert, who runs the University of Rhode Island Plant Protection Clinic.

This year, it is evidentially Newport’s turn. Both Wheeler and Faubert said that next year the tent caterpillars should move on, but right now officials are waiting to see what happens.

A third leaf-eating caterpillar currently inhabiting the island is the familiar Eastern tent caterpillar. Also native, the Eastern tent is a cousin of the forest tent caterpillar. Eastern tent caterpillars create the familiar silky webs nestled in the crotches of trees in gardens and forests.

A fourth problem is the winter moth. Invasive like the gypsy moth, Faubert said the winter moth was introduced to Nova Scotia in the 1930s and spread into Rhode Island by 2004. She said there is currently little damage from winter moths this season.

Experts said that the current rainy cycle aids in the control of caterpillars. The wet weather precipitates a fungus that destroys the pests.

Homeowners currently enduring a caterpillar infestation have a number of allies willing to assist. In addition to dozens of local professional arborists and foresters, there is the University of Rhode Island’s Cooperative Extension. Additionally, the Newport Tree Society has recently issued a press release addressing the problem, suggesting various remedies and insecticides. There is also a wealth of information on line.

People generally don't like moths. They strip forests bare, get into clothes, cereal, hair and leave their droppings on cars. They are not pretty like their cousin, the butterfly, and we don't quite understand why they immolate themselves in flames and artificial lights.

The northeast has more than one thousand species of moths. And in the spirit of the Boston Tea Party, it’s too bad that back in 1869 someone didn't slip that one box of eggs from the cargo ship's hold and overboard into Davy's Jones locker. A whole bunch of trees would have been grateful.

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