Hylesia moths are known to occur in outbreaks and are infamous for their medical importance both as larvae and adults. Among these, the colorful (white, with black and red markings), processionary larvae of Hylesia umbrata Schaus, 1911 occur in large aggregations and pupae communally, yet little is known of their life history. During the dry season of 1999 in Panama, we took the opportunity to collect and dissect a Hylesia umbrata cocoon mass and keep the pupae under laboratory conditions to document the timing of their expected mass emergence and record any parasitoids. These data are presented and discussed, and cases of lepidopterism (contact dermatitis) by Hylesia adults in Panama are reported.