The Forest Tent Caterpillar (Malacosoma disstria) is a species native to North America often encountered in large numbers during cyclical outbreaks. These dense populations frequently lead to questions about their safety, particularly concerning toxicity to humans and pets. The Forest Tent Caterpillar is generally not considered poisonous to people or animals. Concerns about their safety typically arise from their sheer numbers and the fine hairs that cover their bodies.
Are They Toxic or Irritating?
The terms “poisonous” and “venomous” refer to organisms that produce or inject toxins, respectively. Forest Tent Caterpillars are neither poisonous nor venomous; they do not produce or inject toxins harmful upon consumption. However, the caterpillars do have stiff, bristle-like hairs called setae covering their bodies.
These setae can cause a localized reaction known as contact dermatitis in some individuals. The fine hairs act as a physical irritant, triggering an allergic immune response in sensitive people. This is a mechanical or allergic reaction, not a toxic one, comparable to a mild rash from irritating plant fibers. While harmless to most people, the setae can concern grazing animals like horses. Ingesting large numbers of the hairs has been linked to potential reproductive issues in pregnant mares.
How to Identify This Species
Accurate identification is important to distinguish the Forest Tent Caterpillar from other species. Mature larvae grow to be about two inches long and have a dark, hairy body. Their coloration includes a dark bluish or black base with distinct blue bands running along the sides.
The most identifying characteristic is the row of creamy-white or yellow markings running down the center of their back. These markings are often described as keyhole, footprint, or diamond shapes. Despite their name, this species does not spin the large, conspicuous silken tents found in tree limbs like their relative, the Eastern Tent Caterpillar. Instead, they spin thin, silken mats on trunks or branches where they congregate to rest or molt.
Safety Measures and Handling
The primary safety measure is to avoid direct physical contact. The fine hairs can become airborne or detach onto surfaces like furniture and clothing, causing irritation without direct handling. If you need to clear them, use a strong jet of water or a broom to dislodge them. Wearing long sleeves and gloves provides a physical barrier when working in areas with a heavy presence.
If contact with the caterpillars or their hairs occurs, wash the affected skin and clothing with soap and water to remove any remaining setae. For a mild rash, applying an adhesive strip, like clear packing tape, and quickly pulling it off can help remove embedded hairs. Symptoms of a mild allergic reaction, such as a localized, itchy, red rash, can usually be managed with a cool compress or an over-the-counter hydrocortisone cream. While rare, symptoms like difficulty breathing or significant swelling warrant immediate medical attention.