Oral Mucosal Envenomation of an Infant by a Puss Caterpillar Dante Allen Pappano, MD, MPH,* Rebecca Trout Fryxell, PhD,† and Molly Warren, PA-C† Abstract: The term “puss caterpillar” describes the larva of at least two Megalopygidae species common to North America. Accidental con- tact with the hairs (setae) is intensely painful, and serious systemic effects have been reported. We describe the envenomation of an infant through the face and oral mucosa, resulting in severe discomfort, limited oral intake, and vomiting, but no other untoward effects. Key Words: caterpillar, envenomation, Megalopyge (Pediatr Emer Care 2017;33: 424–426) C oincident with the new school year, while young children are confronted with alphanumeric symbols and images of bright- yellow school buses, red apples, and friendly, bright-green anthro- pomorphic inchworms, the less friendly “puss caterpillar” (family Megalopygidae) is prowling playgrounds in search of a suitable site to build its cocoon and pass the winter. 1,2 Unlike its smiling, often spectacled cartoon counterpart, this caterpillar bears venom- ous spines and “setae” capable of inflicting severe pain, among other untoward symptoms. 3,4 Generally, envenomation occurs in older children and adults who are engaged in outdoor activities in the late summer and fall. 5 We report the first known envenomation of an infant, the first oral mucosal envenomation, and the first indoors envenomation inflicted by a caterpillar who managed to crawl inside the victim’s home. CASE On the day of presentation, the father heard the patient, a white male infant just less than 10 months of age, cry out inside their home. He found his young son drooling with something that appeared to be a piece of “carpet fuzz” extending from the infant’s mouth. He removed and examined the object, identifying it as a masticated caterpillar. He noted that his own fingers began to burn and sting where he had touched the caterpillar. The infant then vomited several times. The infant was brought to East Tennessee Children’s Hospi- tal, where he was found to be drooling and crying in distress, but to have no airway compromise. On further examination, his lower lip was swollen; he had a petechial rash on his face (Fig. 1), and fine hair-like projections were noted on his face, buccal mucosa, and right hand. The remainder of his physical examination includ- ing his tongue and posterior oropharynx was normal. In the emergency department, the spines were removed using (3M TM Tegaderm TM , St. Paul, MN) transparent film dressings. Some intraoral portions of the spines were felt to be embedded under the mucosa and could not be removed. The infant received diphenhy- dramine, dexamethasone, ranitidine, ibuprofen, and intravenous fluids prior to admission for observation. Shortly after admission, he was able to tolerate his usual feedings, and he was released the following morning. DISCUSSION “Puss caterpillars, ” the larval form the Megalopygidae, are felt to be the most dangerous of the 50 or so insects in the Lepi- doptera order that are known to cause envenomation in humans in North America. 4,6,7 Known as the flannel moth in the adult form, the larvae of Megalopyge opercularis are informally called by many names, “wooly slug, ”“tree asp, ”“opossum bug, ” and “el perrito” (little dog), which appear to be among the most common. 2 Its closely related cousin Megalopyge (Lagoa) crispata is largely in- distinguishable by the untrained eye. 3 Some believe the sting of the M.(L.) crispata to be less severe, but this is controversial. 6 Certainly, there are many more reports of envenomation by M. opercularis than M.(L.) crispata; however, the accuracy of identification in most cases cannot be ensured. In the case we report, the poor state of the masticated cater- pillar (Fig. 2) obscured distinguishing features, disallowing exact species identification. The basic morphologic appearance and physiologic reaction to envenomation placed it in the family Megalopygidae. Because of regional distribution patterns and in- sect life histories, the specimen was most likely M.(L.) crispata. Most untoward contact between puss caterpillars and humans occurs in the late summer and fall, when the mature “instar” (life stage) of the caterpillar is encountered. 4,8 For M. opercularis, envenomations have been reported from across a wide swath of the southern United States, Mexico, and even as far south as Venezuela. 2,4,9 The greatest number of cases is reported from Texas, where in the past the problem was severe enough to temporarily shut down the San Antonio school system. 10 The North American habitat of M.(L.) crispata covers an even greater geographic area that ranges from the Northeastern United States westward to Oklahoma. 1,6 Indoor exposure has not been reported previously. During the fall, these creatures are actively searching for a suitable location to build a cocoon and pass the winter. Such exploration may be re- sponsible for the unusual indoors encounter described in this case. It is possible that a heavier than usual density of puss caterpillars might make atypical encounters more likely; however, no data are routinely collected on this species’ density by year or region. The setae of Megalopygidae are short and stout with a bulb- like base containing a poison gland. When the setae are stimulated via contact, pressure at the base of the setae causes the toxic com- pounds to be emitted from the hair. 11 There are no barbs, and re- moval using various forms of adhesive-backed material such as tapes has been reported previously. 4,8,12 One author of this case re- port (D.A.P.) found wiping hard with thread-based gauze more ef- fective than Tegaderm (3M, St. Paul, MN) when attempting the removal of hairs from the face, lips, and oral mucosa in a similar case involving a nonvenomous caterpillar species. In the case of Megalopygidae, the exact nature and compo- nents of the venom have eluded discovery, but it appears to be free From the *East Tennessee Children’s Hospital and †Department of Entomol- ogy and Plant Pathology, University of Tennessee Institute of Agriculture, Knoxville, TN. Disclosure: The authors declare no conflict of interest. Reprints: Dante Allen Pappano, MD, MPH, East Tennessee Children’s Hospital, 2018 Clinch Avenue, Knoxville, TN 37916 (e‐mail: epappano@aol.com). Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0749-5161 ILLUSTRATIVE CASE 424 www.pec-online.com Pediatric Emergency Care • Volume 33, Number 6, June 2017 Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.