Walnut caterpillars (Datana integerrima) are a common sight on deciduous trees, particularly walnut and pecan trees, across eastern North America. Their noticeable presence often leads to questions about their potential danger. This article explores their characteristics and addresses safety concerns.
Identifying Walnut Caterpillars
Walnut caterpillars undergo several developmental stages, changing in appearance as they mature. Newly hatched larvae are small and light yellow-green. Middle-sized caterpillars, 0.5 to 1.5 inches, appear dark red with four white stripes. Full-grown walnut caterpillars are distinctly black with long, whitish-gray hairs, and can reach up to 2 inches. When disturbed, these caterpillars exhibit a characteristic defensive posture, raising both their head and the end of their body.
These caterpillars are known for their gregarious nature, often feeding and molting in large groups or colonies. They can frequently be found clustered together on tree trunks or limbs when they are preparing to shed their skins. After molting, they leave behind an accumulation of cast skins, sometimes described as a “hairball,” on the tree. The adult form is a moth with a 1.5 to 2-inch wingspan, typically brown and tan with dark lines on its forewings.
Are Walnut Caterpillars Dangerous?
Walnut caterpillars are generally not considered harmful to humans or pets. They are not venomous, meaning they do not inject toxins, nor are they truly “poisonous” in the sense of causing harm if ingested in small amounts. Their primary defense mechanism involves their appearance and behavior, such as arching their bodies when disturbed, rather than chemical defenses.
While they are not poisonous, some individuals may experience mild irritation upon direct contact with the hairs covering their bodies. This contact can sometimes lead to temporary skin reactions, such as itching or a mild rash. These symptoms are typically minor and resolve without lasting effects. For pets, casual contact or accidental ingestion of a walnut caterpillar is unlikely to cause severe issues, though any unusual symptoms should prompt a consultation with a veterinarian.
Handling Walnut Caterpillars Safely
Interacting with walnut caterpillars generally requires a cautious approach to prevent skin irritation. It is advisable to avoid direct bare-skin contact with the caterpillars and instead use gloves or tools if removal becomes necessary. Simple methods for removal include gently knocking them off branches into a bucket of soapy water, which effectively dispatches them. This method is suitable for smaller trees or localized infestations where caterpillars are easily accessible.
After any potential contact with the caterpillars or infested areas, washing hands thoroughly with soap and water is recommended to remove any lingering hairs. While walnut caterpillars can defoliate trees, especially during outbreaks, natural predators often help manage their populations. Therefore, extensive control measures might not always be needed unless tree health is significantly impacted, allowing for a calm and considered response to their presence.