The asp caterpillar, commonly known as the puss caterpillar, is the larval stage of the Southern Flannel Moth (Megalopyge opercularis). Despite its deceptively soft, furry appearance, this insect possesses a powerful defense mechanism that can cause significant harm upon contact. It is venomous, meaning it actively injects toxins through specialized structures, rather than being poisonous. Its danger lies in numerous hollow spines, or setae, hidden beneath its dense, hair-like exterior, each connected to a venom gland. When the caterpillar is brushed or pressed against the skin, these fragile spines break off and embed themselves, releasing venom that causes an immediate and intense reaction.
Identifying the Asp Caterpillar
The asp caterpillar is typically a compact, tear-drop shaped larva, measuring about one to one-and-a-half inches long when fully grown. The body is completely covered in a long, thick coat of silky hair, which ranges in color from yellowish-white or gray to golden brown or reddish-brown. This dense covering makes the caterpillar resemble a small, walking tuft of cotton.
The creature’s head and legs are mostly obscured from view by the surrounding “fur.” Hidden within this seemingly soft layer are the short, sharp, venom-filled spines that cause the sting. These spines are arranged in rows along the caterpillar’s body, waiting to be deployed if the insect is touched. This camouflage is highly effective, as the innocent look often tempts people to pick it up.
Symptoms Following Contact
Contact with an asp caterpillar results in an immediate and intense reaction. The first and most prominent symptom is a sudden, severe, throbbing pain that is often compared to a broken bone or a bad burn. This pain does not remain localized but can quickly radiate up the affected limb, sometimes reaching the lymph nodes in the armpit or groin.
The site of contact will rapidly develop a rash characterized by a distinct pattern of small, red spots. This unique grid-like pattern marks the exact points where the numerous venomous spines penetrated the epidermis. Beyond the localized pain, the venom can trigger systemic symptoms in susceptible individuals. These may include headache, nausea, vomiting, abdominal distress, fever, and muscle spasms. In rare instances, a severe reaction can lead to swollen lymph nodes, widespread hives, or signs of respiratory distress or shock, which require immediate medical attention.
Immediate Response and Medical Care
The first step after contact is to safely remove the caterpillar without touching it with bare hands, if it is still present on the skin. The most effective method for removing the embedded venomous spines is a technique involving adhesive tape. Gently apply cellophane or medical tape over the affected area, pressing it down lightly, and then quickly strip the tape away to pull out the embedded setae. Repeat this process several times until the entire contact area has been treated.
Once the spines are removed, the sting site should be gently washed with soap and water to prevent secondary infection. Pain management is typically the next concern, and applying a cold compress or ice pack can help reduce the burning sensation and localized swelling. Over-the-counter oral antihistamines can be taken to help alleviate itching.
Professional medical care is necessary if symptoms progress beyond localized pain and rash. Seek immediate attention if the victim experiences difficulty breathing, widespread swelling, intense abdominal pain, or signs of a severe systemic reaction like fever or shock. For severe pain that does not respond to initial first aid, a physician may need to administer stronger pain medication, as common non-prescription pain relievers are often ineffective.
Geographic Range and Prevention
The asp caterpillar’s natural range extends across the Southern United States, and can be found as far north as Virginia and New Jersey, and south into parts of Mexico and Central America. They are often encountered in urban and suburban settings because they feed on the leaves of common host plants. These host plants include deciduous trees, such as oak, elm, pecan, and hackberry, as well as various garden shrubs and rose bushes.
The caterpillars typically have two generations per year, leading to a bimodal peak in human encounters, with activity common in the late spring and a second surge in the fall months. Prevention relies primarily on awareness and caution, particularly during the peak seasons. It is best practice to avoid touching any unfamiliar caterpillar, especially those with a furry appearance. When working in the garden or around host trees, wearing long sleeves, long pants, and gloves can provide a physical barrier against accidental contact.