Calling Caterpillars By The Wrong Name: How gypsy moths came to pillage Connecticut forests

In New England, we are fortunate enough to experience two springs every year: one in May when the first leaves begin to unfurl on the trees, and again in summer when the trees unfurl new leaves to replace the original ones devoured by gypsy moth caterpillars. (Kent McFarland/Creative Commons)

In New England, we are fortunate enough to experience two springs every year: one in May when the first leaves begin to unfurl on the trees, and again in summer when the trees unfurl new leaves to replace the original ones devoured by gypsy moth caterpillars. (Kent McFarland/Creative Commons)

In New England, we are fortunate enough to experience two springs every year: one in May when the first leaves begin to unfurl on the trees, and again in summer when the trees unfurl new leaves to replace the original ones devoured by gypsy moth caterpillars.

It wasn’t always like this – not until the turn of the 20th century did our second spring begin to come around, spreading west, north, and south from just outside Boston.

The cause for this second spring has nothing to do with the celestial ballet of the Earth and Sun, but rather an enterprising painter looking to make a mark in the North American silk industry and bad taxonomy.

From the kingdom down to the species, taxonomy, the science of naming and classifying life on Earth, provides a hierarchy for organizing life on Earth. In the process, taxonomy breaks the biological world up in a way our minds can make sense of, but more importantly it tells us something about which species are closely related to each other and which are not. This system of classifying life, invented by by the Swedish botanist Carl Linnaeus in the early 1700s, is still the dominant way we look at life today.

In the mid 1800s a painter named E. Leopold Trouvelot was living on a tree-lined street in Medford, Massachuetts just outside of Boston. Beyond painting, Trouvelot was drawn to the giant caterpillars of North America – the silkworms. There are thousands of species of caterpillars in North America, but not many that get as large as the silkworms, so it’s not surprising Trouvelot took an interest in them.

He was intrigued by more than just their size; he was looking to start a new silk industry.

Most species of silkworms wind a cocoon made of silk, which protects them as they undergo metamorphosis and grow into a moth. Sericulturists, or silk-makers, take these cocoons and unwind them to produce a single a strand of silk that is later combined with the silk from other cocoons to form sheets and garments. This practice is still done to this day with the domestic silkworm (Bombyx mori), a species of silkworm native to Eurasia.

Mansfield was actually the site of the first silk mill in the United States, which was built just east of campus at Hanks Hill in 1810, and for many years Mansfield led the nation in silk production. Rows and rows of mulberry trees, the food for these caterpillars, would have blanketed the landscape back then.

By the 1860s a disease was causing a decline in the mulberry trees, and the Civil War made it difficult to get other textile materials like cotton to the North. Trouvelot began experimenting with ways to get silk from other silkmoths. He set his sights on the gypsy moth. The gypsy moth may seem an odd choice for silk farming –  taxonomy today tells us this species is not closely related to the silkmoth at all.

Why did he think he could draw silk from it?

Well, taxonomy has come a long way since the 1860s. When Trouvelot was doing his work in the 1860s and 1870s, we were only about 100 years down Linnaeus’ path of rigorously identifying and classifying life on Earth, so one would forgive any misclassification of the era.

Unfortunately, we are still dealing with the mess from one of these misclassifications. At the time of Trouvelot’s experiments both the gypsy moth (Lymantria dispar) and the domestic silkmoth (Bombyx mori) were grouped in the same family and same genus. Some taxonomist thought they were closely related and put them together.  For Trouvelot, Bombyx mori was Lymantria mori. So when Lymantria mori started to have some trouble producing silk, he looked for the next best thing: Lymantria dispar, better known as the gypsy moth.

Toruvelot visited France in the late 1860s and returned with gypsy moth egg masses in tow. Being in the same genus, Trouvelot thought they must make a similar quality silk, but the silk of the gypsy moth couldn’t hold a candle to that of the domestic silkmoth.

Trouvelot’s experiments were failing, and his caterpillars were escaping from the tree he in his backyard. Worried about the release of these non-native caterpillars, he contacted local entomologists, who showed little interest in the problem. Ten years later, with his street as the epicenter, came the first outbreak of gypsy moths in North America.

The range of the gypsy moth now extends west to Michigan and south to North Carolina. While recent attempts at slowing its spread have showed promise, the gypsy moth continues to expand its range, causing millions of dollars in damage every year and altering the forests around us. Taxonomy may seem an arcane endeavor, but at times getting the name right can mean a world of difference.


Kevin Keegan is a campus correspondent for The Daily Campus. He can be reached via email at kevin.keegan@uconn.edu.