These were on my Ornamental Plum. I swear I have had every creepy insect, worm, whatever eating my plants this year!

Saddleback caterpillars.... very painful stingers. The spines of Acharia stimulea are strong, acutely pointed, and hollow. They embed deeply into tissue and break off, and can interrupt healing as the protoplasm from the venom glands dries into the tissue area (Gilmer 1925). The venom itself can cause a systemic condition called erucism or acute urticaria, for which severe symptoms may include migraines, gastrointestinal symptoms, asthma complications, anaphylactic shock, rupturing of erythrocytes, and hemorrhaging (USAF 1982, Hossler 2009).

Physically manifested symptoms may or may not be present with erucism (Hossler 2009). Contact dermatitis caused by Acharia stimulea includes immediate intense burning sensations around the contact zone, arector pili muscles tightening causing hair to stand on end, increased perspiration in the affected area, red blanching of the skin, and blistering (Edwards et al. 1986; Hossler 2009, 2010). Symptoms can last for five hours, and leave red blotches in the envenomation site (Hossler 2009).

Prevention of stings is the most effective measure when faced with erucism hazards: protect skin with long sleeves, pants, and gloves when anticipating potential contact with Acharia stimulea, and avoid areas of heavy infestation if known (USAF 1982; Hesler et al. 1999; Gottschling et al. 2007; Hossler 2009, 2010). Should contact occur, the removal of spines should always take precedence as the longer spines are embedded in tissue the more venom is administered (Hossler 2009, 2010). Other symptoms should be treated on a case by case basis tailored for your specific reaction by a certified physician (Hossler 2009, 2010).

Personal repellants, such as DEET, are not effective controls for Acharia stimulea. Manual removal of eggs, larvae or cocoons with proper protective wear and tools is an effective method of control in case of unpredicted population increase (Benaim-Pinto et al. 1991, Gottschling et al. 2007, Iserhard et al. 2007). Spines of urticating caterpillars can become airborne and consequently be inhaled or contact sensitive tissues like the eyes and nose. They may also embed in surfaces such as wooden tables and plastics, which become a contact hazard at a later time if the area is not cleaned. Stray spines can also get caught in fabrics, such as carpet, aprons and clothing and come into skin contact that way