The Medford Storm
Sometime around 1868 or 1869, a storm struck Medford, Massachusetts, and tore apart the nets in which Étienne Léopold Trouvelot was keeping his caterpillar specimens. The caterpillars were European spongy moths, known to science as Lymantria dispar (and called the “European gypsy moth” until the Entomological Society of America changed the common name in 2022), and they escaped. No source records how many got out or the exact date. What is recorded is the outcome: a breeding program ended, and a second career began.
The Exile’s Ambition
Trouvelot was born on December 26, 1827, in the Aisne region of northern France, and trained as a lithographer. When Louis-Napoléon Bonaparte staged his coup d’état on December 2, 1851, Trouvelot was among those with reason to leave. He arrived in the United States in 1852 and settled in Medford, where he joined the Boston Natural History Society and took up entomology as an amateur. His project was an attempt to breed a disease-resistant, silk-spinning hybrid by crossing silkworms with European spongy moths. Whether it had any reasonable biological prospect of success the historical record does not address. It addresses the storm, the torn nets, and what followed.
One account states that Trouvelot reported the escape in writing and by word of mouth; another holds that no evidence survives of any notification to officials. The sources disagree, and no documentary proof has settled the matter.
The Pivot to Astronomy
In 1870, Trouvelot left Medford for Cambridge, Massachusetts. What is corroborated is that he was making documented astronomical observations by early 1872: his plate of the Aurora Borealis is dated March 1, 1872. Joseph Winlock, director of the Harvard College Observatory, noticed the work. In Winlock’s recorded assessment, as preserved by Naval Observatory librarian Brenda G. Corbin, Trouvelot combined the qualities of an excellent observer with the skills of an accomplished artist. Winlock brought him to the observatory, where Trouvelot worked with a 15-inch (38 cm) refractor, joining the staff in 1872.
In 1875, he received an invitation to the United States Naval Observatory in Washington, D.C. where the main instrument was a 26-inch (66 cm) refractor, then the largest refracting telescope in the world. He used it for approximately one year. Among the results was his documented observation of what he identified as veiled sunspots, a solar feature he is credited with recognizing that year.
The Mechanics of Precision
Between 1870 and 1890, Trouvelot produced an estimated 7,000 astronomical illustrations covering planets, comets, solar phenomena, and nebulae. Curator Krystle Satrum, in a 2018 exhibition at the Huntington Library, described a grid system he used: a grid over the telescope lens matched a corresponding grid on his drawing paper, allowing proportions to be transferred accurately. His years of biological fieldwork left a visible mark on the images; the solar prominences he drew on May 5, 1873, bear a noted resemblance to veins and cardiac chambers.
In 1876, fifteen of his pastel illustrations appeared at the Centennial Exposition in Philadelphia. In 1882, Charles Scribner’s Sons published a portfolio of fifteen chromolithographic plates, The Trouvelot Astronomical Drawings, with roughly 300 sets printed at an original sale price of $125 per set. Trouvelot also produced a scientific manual and approximately 50 papers.
Return to France
Trouvelot returned to France in 1882. The French Academy of Sciences awarded him the Valz Prize for astronomy that year. He joined the Meudon Observatory outside Paris, working under director Jules Janssen, and described the Parisian skies as “cloudy and vaporous.” He died at Meudon on April 22, 1895, while working on a monograph about Mars. A lunar crater roughly 5.6 miles (9 km) in diameter and a Martian crater approximately 92 miles (148.77 km) across both carry his name.
The Ecological Bill
The first recorded defoliation linked to the escaped moths was in 1889, in the Medford neighborhood where Trouvelot had kept his specimens, across an area estimated at around 360 square miles (approximately 932 km²). By the 1890s, the infestation was established across Massachusetts and eventually reached Wisconsin. An outbreak can strip an entire forest canopy in a single growing season, leaving trees to recover or die depending on how many successive years they are hit.
The eastern forests paid the bill. Trouvelot did not.
The Unresolved Record
Two gaps remain. The number of moths that escaped is unrecorded, and any figure would be speculation. The specific parameters of the hybridization project, what strains Trouvelot was using and how far the work had progressed, are likewise undocumented. What is documented is that by the 1890s the descendants of whatever came through those torn nets had spread across the eastern United States, while Trouvelot lay dead in Meudon with his Martian monograph unfinished and Parisian clouds overhead.