Lepidopterism is a term that refers to a spectrum of medical conditions, typically involving the skin, that result from contact with the adult or larval forms of certain butterflies and moths. There are more than 165,000 species of these insects, however, only about 12 species are known to harm humans, most commonly in the form of contact dermatitis. Among these species, the Megalopyge opercularis, commonly called the "Puss Caterpillar", is known to cause a painful and pruritic cutaneous reaction when its venom encounters the skin. Although caterpillar stings are not a common etiology of dermatological rashes, physicians must perform a detailed history and have a high degree of suspicion to arrive to the correct diagnosis and avoid unnecessary medications and therapeutics. We present a case of a 14-month-old boy who presents to the pediatric clinic with a unilateral red rash on the anterior aspect of the left leg, from the distal thigh to the shin. The parents report that the boy was sitting in the park, when he suddenly started to cry. They state that the rash began to spread and that red marks are growing. The patient's parents brought the caterpillar specimen in a bag, clinching the diagnosis. The patient was treated with antihistamine drugs for symptom relief and was recommended to wash thoroughly the area with soap and water. The patient returned to the clinic four days later and the rash had resolved. When encountering an acute onset rash in a patient with recent exposure to nature environments and other open spaces with trees, lepidopterism should be considered in the differential diagnosis and promptly treated. Furthermore, the physician must educate the patients on how to avoid exposure, and special care should be implemented with asthmatic and atopic patients, because although rare, anaphylactic reactions to these stings have been reported.