The puss caterpillar (Megalopyge opercularis), the larva of the Southern Flannel Moth, is one of the most venomous caterpillars in North America. Its fur-like appearance, which earns it nicknames like “puss” or “asp,” hides a serious defensive mechanism. Beneath the dense, silky hairs are rows of tiny, hollow spines containing a potent venom. Contact causes these spines to break off and embed in the skin, releasing a painful toxin that can lead to severe reactions. Safe removal requires immediate, non-contact methods and long-term environmental management.
Identifying the Threat and Habitat
The puss caterpillar is approximately 1 to 1.5 inches long and is recognizable by its dense coat of long, silky hairs (setae), giving it a teardrop shape. This furry exterior varies in color, ranging from creamy white to gray, golden brown, or reddish-brown, often blending with tree bark.
Puss caterpillars are found in the southeastern United States, from the Carolinas to Texas. They are most commonly encountered during two distinct generations annually, peaking in late spring to early summer and again in late summer or early fall. These caterpillars feed on the foliage of various deciduous trees and shrubs, including oak, maple, elm, sycamore, and pecan. While naturally found in wooded areas, their presence on low-hanging branches in residential areas poses a direct risk of accidental contact.
Immediate, Non-Contact Removal Methods
Removing a puss caterpillar requires strict adherence to a non-contact protocol to avoid the venomous spines. Wear thick gloves, long sleeves, and safety glasses, as spines can detach or transfer indirectly. The goal is to physically dislodge the specimen into a container for immediate disposal.
A safe method involves using a long-handled tool, such as a scraper, stiff cardboard, or a trowel, to gently scrape the caterpillar off its resting surface. Direct the insect into a sealable glass jar or sturdy plastic container. Once the caterpillar is secured inside, the container must be tightly sealed immediately.
Disposal Methods
The sealed container can be placed in a freezer overnight, which is a standard method for euthanizing invertebrates. Alternatively, place the secured caterpillar into a bucket of water mixed with dish soap. The soapy water mixture breaks the surface tension, causing the insect to drown rapidly. Remember that dead caterpillars can still deliver a painful sting from their venomous hairs, so dispose of the container or water with caution.
Long-Term Prevention and Population Management
Controlling the puss caterpillar population requires targeting both the larval and adult stages of the Southern Flannel Moth. Regular scouting and pruning of host plants is an effective cultural control, especially during peak seasons (late spring and fall). Infested branches, where caterpillars are clustered, can be carefully clipped and immediately sealed in a bag for disposal, removing the localized threat.
The life cycle presents a vulnerability in the form of the cocoon, where the second generation overwinters before the adult moth emerges in the spring. These tough, silk cocoons are often found attached to twigs or hidden in bark crevices on host plants. Inspecting and scraping off these cocoons during the winter months significantly reduces the following year’s population.
Targeted chemical control must be timed correctly for maximum effect. Applications of Bacillus thuringiensis var. kurstaki (Btk), a naturally occurring soil bacterium, are highly effective against young caterpillars when ingested while feeding. Btk is less effective on larger larvae, making early season application a priority. For severe infestations, a professional application of a residual insecticide (e.g., permethrin or cyfluthrin) may be used as a last resort to create a barrier and achieve quick knockdown.
First Aid for Puss Caterpillar Stings
Despite precautions, accidental contact requires immediate first aid to manage the severe pain. The first step is to remove any embedded venomous spines (setae) from the skin. Gently press adhesive tape (such as packing or medical tape) onto the affected area and quickly pull it off. Repeat this process multiple times with fresh pieces of tape to ensure maximum removal of the microscopic spines.
After removing the spines, wash the sting site thoroughly with soap and water. Pain relief can be managed by applying an ice pack or cold compress to reduce swelling and discomfort. A baking soda slurry, calamine lotion, or oral antihistamines can help manage localized swelling or itching. Intense pain that radiates up the limb, or systemic symptoms like nausea, headache, chest pain, or difficulty breathing, require immediate emergency medical attention.