**Nettle Caterpillars** (family Limacodidae, most often referring to the **Saddleback Caterpillar** (*Acharia stimulea*) or related slug moth larvae) are characterized by their smooth, slug-like appearance and, most importantly, the presence of **urticating (stinging) hairs or spines**. They are generalist feeders on the foliage of many deciduous trees and shrubs. The conflict is direct physical contact: brushing against or handling the caterpillars results in a **painful sting**, swelling, rash, and localized nausea, posing a significant stinging hazard to gardeners, arborists, and children.
Taxonomy and Classification
Nettle Caterpillars belong to the order Lepidoptera. They undergo complete metamorphosis. The stinging defense is highly effective against predators. They are called “slug moths” because the larvae lack the characteristic prolegs of most caterpillars, giving them a smooth, crawling movement.
Physical Description
Mature Nettle Caterpillars are 1 to 1.5 inches long.
- **Appearance (Key ID):** Smooth, plump, legless, often brightly colored, and covered in clusters of hollow, venom-tipped **spines** (e.g., Saddleback has a distinctive green “saddle” on a brown body).
- **Stinging Mechanism (Key ID):** The contact with the spines causes the venom to be injected into the skin, resulting in immediate, intense, burning pain.
- **Damage Sign:** Irregular holes or marginal feeding damage on host plant leaves, though the damage is usually minor and overshadowed by the stinging hazard.
- **Conflict:** Direct stinging hazard to humans.
Distribution and Habitat
Nettle Caterpillars (Limacodidae) are found worldwide, concentrated in tropical and temperate regions. Their habitat is the foliage of a wide variety of deciduous and ornamental plants, where they often feed gregariously in high numbers.
Behavior and Conflict
The conflict is purely medical/defensive.
- **Defensive Sting:** They are not aggressive but deliver the sting when pressure is applied or they are touched.
- **Medical Treatment:** Immediate application of adhesive tape over the area and rapidly peeling it off can help remove embedded spines. Ice packs and antihistamines can reduce pain and swelling. Seek medical attention if a severe systemic reaction (difficulty breathing) occurs.
- **Seasonal Abundance:** They are usually encountered in late summer and fall as they complete their final instars before pupating.
Management and Prevention
Control is integrated pest management (IPM), favoring manual removal when necessary.
- Teach children and pets to avoid contact. Wear gloves and long sleeves when pruning or harvesting plants known to host these pests.
- If necessary, remove the caterpillars using long-handled tweezers or a gloved hand and destroy them.
- General caterpillar insecticides (like *Bacillus thuringiensis* (Bt)) are effective when the caterpillars are small, but treatment is usually unnecessary unless populations are exceptionally high.
Conservation and Research
Nettle Caterpillars are managed as a public health nuisance. Research focuses on the composition of their venom, the effectiveness of medical treatments for the sting, and their general biology and host range.