The spongy moth, now widely recognized by its updated common name, is a well-known insect that poses a significant threat to forests across various regions. Originally known as the “gypsy moth,” its name was formally changed to “spongy moth” in March 2022 by the Entomological Society of America to remove a term considered an ethnic slur. This defoliating pest has a widespread impact, leading many to question its origins and how it became so prevalent.
Native Range
The spongy moth is indigenous to a broad geographic area spanning Europe, Asia, and parts of North Africa. In its native habitats, the moth inhabits deciduous and mixed forests, where its populations are naturally regulated by predators and pathogens. The caterpillars feed on the foliage of a wide variety of trees, including oaks, birches, and maples.
Small mammals, including deer mice, prey on the moth’s pupae and caterpillars. Birds like cuckoos and chickadees also feed on different life stages of the moth. Additionally, naturally occurring fungi, such as Entomophaga maimaiga, and viruses, like the nucleopolyhedrosis virus (NPV), help to control outbreaks by causing disease among caterpillar populations. These biological controls contribute to keeping the moth’s numbers in check within its original ecosystems.
Arrival in North America
The introduction of the spongy moth to North America was an unintentional event rooted in a scientific experiment. In 1869, Étienne Léopold Trouvelot, a French naturalist residing in Medford, Massachusetts, imported spongy moth egg masses from France. His primary goal was to cross-breed these moths with silkworms to develop a hardier, disease-resistant variety for silk production, hoping to establish a domestic silk industry. At the time, the potential for invasive species was not well understood, and the practice of importing insects was not subject to the strict regulations seen today.
Trouvelot conducted his experiments at his home, where he cultivated a large number of caterpillars. Accounts suggest that some of the moths accidentally escaped from his property in Medford. Despite Trouvelot reportedly notifying local authorities of the escape, his warnings were largely unheeded, as the immediate threat posed by the few escaped caterpillars was not recognized.
Subsequent Spread
Following its initial escape in Medford, Massachusetts, the spongy moth began to spread across North America. Within approximately 20 years, by 1889, significant defoliation was observed in the trees around Medford, indicating a growing population. The moth’s spread occurred through both natural dispersal mechanisms and human-assisted transport.
Natural spread primarily involves the wind dispersal of young larvae, a process known as “ballooning.” Small caterpillars can produce silk threads that catch the wind, allowing them to travel short distances. However, stronger winds can carry them much further, facilitating their expansion into new areas.
Human activities have significantly accelerated the moth’s dispersal, as egg masses are often laid on various outdoor items such as firewood, vehicles, recreational equipment, and nursery stock. When these items are moved, the egg masses are inadvertently transported to new locations, leading to new infestations. From its initial point, the spongy moth has expanded its range throughout the northeastern United States and into eastern Canada, including provinces like Ontario, Quebec, New Brunswick, Prince Edward Island, and Nova Scotia.