On the wall of my office is a beautiful map of Kentucky, shown below. The other pictures are a crater on Mars, a drawing of Jupiter, and gypsy moths. All of these images are connected by one person, Étienne Léopold Trouvelot, a self-educated cartographer, astronomer and entomologist. This is the story of Trouvelot’s Folly – the deliberate and disastrous introduction of the gypsy moth to North America. Scroll below the figure to read more.
Trouvelot made his living as an illustrator, first in his native France, later in the small town of Medford, Massachusetts. In 1877, Trouvelot was hired by the Kentucky geologist Nathaniel Shaler to draw maps for the Kentucky Geological Survey. During their discussions, Trouvelot shared shocking news with Shaler – he was raising moths in his back yard, including gypsy moths imported from Europe, in the vain hope of creating a domestic silk industry. (For a full account of gypsy moth in America, see the fine book by Robert Spear, 2005, The Great Gypsy Moth War.)
Shaler was a good enough naturalist to realize the dire consequences of Trouvelot’s deed. Shaler later recounted his reaction: “About thirty years ago I had in my employment a Frenchmen, a remarkable man, who was exceedingly experimental…He had the idea of bringing, and had already brought from Europe, specimens of the gypsy moth, with a view of crossing them with some American moths, in order that he might get a hybrid silkworm that would feed on oak leaves. Learning of it I spoke to him about it and told him of the risk which he was running, the risk of settling a pest with us…I begged him to destroy the creatures, which he told me he would” (quoted in Spear 2005).
Gypsy moth caterpillars are powerful wanderers, capable of slipping through small holes in the netting that Trouvelot used to contain his subjects. Trouvelot may have been sincere in when he promised Shaler that he would destroy his insects, but it was already too late. By the time Trouvelot was ready to quit his failed silk enterprise, there were caterpillars and egg masses all over the neighborhood.
Trouvelot turned his considerable abilities to astronomy, making some of the finest and most detailed drawings of the sun and planets. He was on the staff of Harvard University and used the telescope of the US Naval Observatory, gaining considerable fame with astronomers and the public for his work. Astronomers honored him by designating Trouvelot Crater on the Moon and Trouvelot Crater on Mars. The Martian crater is considered a potential landing site for future Mars missions.
Trouvelot returned to France in 1882, long before most people were aware of what his moth experiments had unleashed on the United States. As Spear recounts, Trouvelot was aware that his gypsy moths were escaping but never told his neighbors.
Over the next few years, gypsy moths spread through Medford, at first only annoying a few neighbors. Then, after a mild winter that allowed many eggs to survive, the gypsy moth exploded in 1889. Witnesses reported vast hordes of caterpillars turning roads and railroad tracks slick, and stripping large trees of all their leaves in a few minutes. There are accounts of workers destroying 100 tons or more of caterpillars. At that point, what had been a nuisance became a crisis. The caterpillars were defoliating apple, pear, maple and oak trees alike, and even devouring garden crops.
There are two ways to deal with a new pest or pathogen – try to exterminate it, or try to manage it. Attempts to exterminate an invader is a form of warfare, marshaling vast resources against the enemy. War rarely succeeds against an invader unless it has a small beachhead of a few individuals. As we will see, management would have been a better strategy.
Charles Henry Fernald was a professor of zoology at the University of Massachusetts. Medford citizens sent samples to him of the unknown, unnamed caterpillar. Entomology was a family affair in the Fernald household and Fernald’s wife Maria and son Henry received the first caterpillars while Charles was out of the country. They carefully reared adults and were able to identify them as gypsy moth, Lymantria dispar. Well known in Europe and Asia, the insect had never been seen in the Americas.
When Fernald returned, he and other entomologists set out fight a war against the gypsy moth. As the crisis grew to engulf much of Massachusetts, Fernald gained the attention of the state’s political powers with a plan to exterminate the invader. Eradication efforts began with attempts to destroy egg masses with kerosene torches, but there were too many. Fernald turned to one of the few insecticides then available: Paris green.
If you are a fan of Victorian murder mysteries, you may be familiar with Paris green, a common poison both in fiction and in real life (including an episode of Boardwalk Empire). A mixture of arsenic and copper, it has the reputation of being lethal to any animal, including humans, that comes in contact with it. Paris green was used as a poison, as a pigment for paints and even as an ingredient in fireworks. Paris green is no longer used because of its high toxicity, though other pesticides containing arsenic are still on the market.
As the army of gypsy moth caterpillars grew, so did an army of laborers scorching trees with fire and spraying Paris green with abandon. The war went on for decades, but it was a failure, doomed from the start. The weapons used were too weak, the gypsy moth too well established and too adaptable. The years in which gypsy moth quietly munched on trees in Medford while Trouvelot told no one gave the insect plenty of time to spread out and prepare for war. Equally important, the adoption of the ‘war’ strategy prevented more sensible management methods from being tried.
Entomologists and foresters knew from the beginning that gypsy moths in Europe and Japan had many natural enemies – beetles, wasps and fungi that held the insect check. A few feeble attempts were made to use these biological controls, but they did not have the popularity or political cachet of going to war. Lacking political support, the management supporters also lacked funding. The warriors got all the money.
Spear argues that the war strategy served the needs of the new discipline of economic entomology. If entomologists could eliminate the gypsy moth with a huge, well-publicized and state-funded effort, they could then make a case for extending their efforts to other economically important insect pests.
The war failed. The gypsy moth is still with us, still expanding its range, still infesting our forests. Over the decades since about 1930, a management approach began to take over. We have to live with Trouvelot’s Folly, the gypsy moth, so the question is whether we can learn to manage the insect to slow its spread and reduce its impacts.
As we will see in Part II, management of the gypsy moth, instead of war against it, is proving quite successful.