Eastern Tent Caterpillars appear across North America in early spring, known for constructing distinctive silken tents in tree crotches. These social caterpillars emerge from their eggs and build communal nests, often causing concern among property owners and animal handlers regarding their potential danger, particularly the question of whether they are poisonous.
Understanding the “Poisonous” Question
Eastern Tent Caterpillars are not poisonous in the traditional sense, meaning they do not produce toxins that are harmful if ingested. The term “poisonous” typically refers to substances that cause illness when swallowed or absorbed internally. Instead, these caterpillars are classified as urticating, meaning they can cause an irritating reaction upon contact. Their bodies are covered with numerous fine hairs, known as setae, which are responsible for these irritating effects. Their defense mechanism relies on these specialized hairs, which can embed themselves in skin or mucous membranes. This mechanism is primarily a physical irritant rather than a chemical one.
Effects of Encountering Eastern Tent Caterpillars
Contact with Eastern Tent Caterpillars can lead to various reactions, primarily due to their urticating hairs. In humans, direct skin contact often results in dermatitis, characterized by an itchy rash, redness, and mild swelling. These symptoms typically resolve on their own within a few hours to a few days, depending on the individual’s sensitivity and the extent of contact. While uncomfortable, these reactions are generally not severe.
The effects on animals can be more concerning, particularly for horses. If horses accidentally ingest Eastern Tent Caterpillars, either by consuming contaminated forage or drinking water with caterpillar remnants, they can develop a condition known as Mare Reproductive Loss Syndrome (MRLS). This syndrome can lead to abortions in pregnant mares, early fetal losses, or other reproductive problems. The exact mechanism of MRLS is thought to involve the caterpillar hairs penetrating the intestinal lining, allowing bacteria to enter the bloodstream and cause systemic inflammation. Other domestic animals, such as dogs and cats, may experience mild gastrointestinal upset if they ingest the caterpillars. This might manifest as temporary vomiting or diarrhea.
Identification and Avoiding Contact
Eastern Tent Caterpillars are relatively easy to identify by their appearance and behavior. The caterpillars are dark, typically black with a prominent white stripe down their back, flanked by blue and yellow markings, and grow to about 2 inches in length. Their most distinguishing feature is the silken tent-like communal nest they construct, usually in the crotches or forks of cherry, apple, and other deciduous trees.
To avoid contact, keep a safe distance from these tents and the caterpillars. When working in areas where they are present, wearing long sleeves, gloves, and protective eyewear can help prevent skin exposure to their hairs. Property owners can physically remove small tents by hand, ensuring they wear appropriate protective gear, or contact a pest management professional for larger infestations. Regularly inspecting trees and forage for caterpillars or their tents helps minimize the risk of accidental ingestion by livestock.