Caterpillar venom apparatus typically consists of barbed spines arranged in clumps or scattered on the dorsal surface of the insect. These are purely defensive in nature. Patients who are stung commonly have intentionally handled the insect or have had accidental skin contact while gardening. Envenomated patients typically present with acute pain followed by focal erythema and swelling. Caterpillars with a less sophisticated venom apparatus or low-potency venom may cause simple focal pruritus or urticaria, although some caterpillars are capable of producing a very painful sting requiring aggressive pharmacologic pain control. Systemic symptoms are rare. The puss caterpillar, or wooly slug (Megalopyge opercularis), is perhaps the most well-known and important venomous caterpillar in the United States. Wooly slug caterpillars have a widespread distribution, appear hairy and flat, and may reach a length of 4 cm.
Caterpillar with Barbed Spines. Typical garden caterpillar with barbed spines arranged in clumps. (Photo contributor: Alan B. Storrow, MD.)
Caterpillar Sting. Appearance of a caterpillar sting at 2 hours. The patient presented with moderate pain and severe itching. Note how the erythema follows the pattern of the caterpillar. (Photo contributor: Alan B. Storrow, MD.)
Puss Caterpillar. The “puss caterpillar” or “woolly slug” is likely the most important venomous caterpillar in the United States. The hairy appearance and small hair tail are characteristic. (Photo contributor: Alan B. Storrow, MD.)
Centipede. Note the curved “fangs” (actually modified legs) on the first segment of this centipede from Texas. (Photo contributor: Alan B. Storrow, MD.)
Centipede. This dead centipede was retrieved from the photographer’s shoe the day after he developed diffuse urticaria for no apparent reason on a trek in Nepal. (Photo contributor: Ken Zafren, MD.)
Chigger Bites. Chigger bites on a leg appear as puncta surrounded by erythema. (Photo contributor: Kevin J. Knoop, MD, MS.)
Chiggers are the larvae of trombiculid mites and may inflict multiple intensely pruritic bites on their victims. They are parasitic only as larvae. They infest humans by crawling onto them and latching on. Proper clothing precautions and repellents are usually effective in reducing unpleasant chigger infestations.
Centipedes are venomous arthropods that have one pair of legs per body segment. The 1st segment contains hollow curved “fangs” (really modified legs) bearing venom glands at the bases, which are capable of penetrating human skin. Centipedes generally ...