In the insect world, appearances can be deceiving. A cute, fuzzy or brightly colored exterior, may hide a painful surprise when handled carelessly. Caterpillars, the immature stages of butterflies and moths, are not usually intimidating, but some should be approached with caution.
Many caterpillars have bodies covered with pointed or barbed hairs for defense against predators. These hairs can produce irritation and rashes when they come in contact with human skin. Some species have hollow, stinging hairs with poison glands at the base called urticating setae. These special defensive hairs can puncture the skin and break, releasing a venom. This venom produces a painful burning sensation and inflammation in many people.
Slug caterpillars are varied in appearance with bodies bearing long fleshy lobes covered with brown hairs or colorful triangular projections. The most common species, the saddle back is distinctive, with a charcoal grey body and lime green saddle across its mid-section.
The largest stinging caterpillar commonly encountered is the larva of the Io Moth. The mature larvae can reach lengths of 2.5 inches. These caterpillars are lime-green in color with bright horn-like spines and four rows of stinging hairs.
Stinging caterpillars are generally not encountered in large numbers. Many are solitary feeders on a wide variety of smooth-leafed shrubs and trees, though the saddle back has been found associated with garden crops including corn. These caterpillars have one or two generations per year and transform into plain brown moths.
The majority of caterpillar stings result from careless handling or brushing against trees and shrubs while mowing the lawn or doing other yard work. Since these insects are rarely encountered and occur in low numbers no chemical control is needed. The best ways to prevent stings are education and avoidance. Admire that colorful or cute and fuzzy caterpillar from afar and walk away with a pleasant memory not a burning irritation.