Forest tent caterpillars are a common sight across North America, often appearing in large numbers. This can raise concerns about their impact on trees and human health. This article clarifies the nature of these caterpillars and their interactions with humans and the environment.
Identifying Forest Tent Caterpillars
Forest tent caterpillars are distinct in appearance, typically growing to about two inches long when mature. Their bodies are predominantly blue and black, featuring a prominent row of white, footprint-shaped or keyhole-shaped markings along their backs. Numerous hairs cover the sides of their bodies.
These caterpillars are native to North America and are found in areas with hardwood trees, favoring species such as aspens, oaks, birches, and maples. Larvae typically hatch from egg masses in early to mid-May, coinciding with the budding of host trees. They feed actively for approximately five to six weeks before pupating. Unlike some other caterpillar species, forest tent caterpillars do not construct large silken tents. Instead, they spin inconspicuous silken mats on tree trunks or branches where they gather to rest or molt.
Are They Toxic? Understanding the Risk
Forest tent caterpillars are not poisonous, meaning they do not inject venom or produce internal toxins harmful if ingested. The primary concern for humans stems from their numerous body hairs. These fine hairs can cause skin irritation, itching, or rashes in sensitive individuals upon contact.
The reaction to these hairs is typically physical, rather than chemical. Symptoms may include redness, swelling, itching, welts, and sometimes small blisters. The hairs can also become airborne or be left behind on surfaces, causing irritation even without direct contact. While most reactions are mild and localized, some individuals may experience a mild allergic response. However, severe allergic reactions, such as anaphylaxis, are extremely rare.
If pets or children ingest forest tent caterpillars, it generally does not result in systemic poisoning. However, the physical irritation from the hairs can lead to mild digestive upset, such as drooling, discomfort, vomiting, or diarrhea. While certain caterpillars have been linked to spontaneous abortions in mares if consumed in large quantities, forest tent caterpillars specifically have not been widely associated with this issue.
Safe Handling and Management
When encountering forest tent caterpillars, avoid direct skin contact. If removal is necessary, wearing gloves can prevent irritation. Caterpillars can be dislodged from surfaces using a stick or a strong stream of water from a hose.
Should skin irritation occur from contact with the caterpillar hairs, wash the affected area promptly with soap and water. Applying adhesive tape to the irritated skin and then pulling it off can help remove embedded hairs. For symptom relief, cold compresses or ice packs can reduce swelling and pain. Over-the-counter hydrocortisone creams or oral antihistamines may also alleviate itching and inflammation.
Forest tent caterpillar populations can occasionally reach outbreak levels, leading to significant defoliation of trees. Despite extensive leaf loss, most trees are resilient and typically recover, often regrowing their leaves within the same season. While large numbers of caterpillars can be a nuisance, they seldom cause lasting harm to healthy trees.