Larvae of Periphoba hircia (Cramer) (Lepidoptera: Saturniidae) defoliated Acacia mangium in the state of Roraima, Brazil. This is the first report of this species defoliating A. mangium in Brazil. The damage to the foliage was substantial and P. hircia should be monitored to ascertain its significance as pest of this plant. The larval stage of this species had 6 instars. Its cocoons were woven either on A. mangium leaves or in the soil. The pupal period of P. hiricia reared on A. mangium lasted 6 months. Its adults were dimorphic with females larger and having more prominent abdomens than males. Larvas de Periphoba hircia (Cramer) (Lepidoptera: Saturniidae) desfolharam plantas de Acacia mangium no estado de Roraima, Brasil, sendo este seu primeiro relato nessa essencia florestal no Brasil. A desfolha foi substancial e essa espécie deve ser monitorada para determinar sua importância para esta planta. A fase de larva teve 6 ínstares. Seus casulos foram tecidos em folhas de A. mangium ou no solo. O estágio de pupa de P. hiricia em A. mangium durou 6 meses. Adultos dimórficos com fêmeas maiores e abdomen mais proeminente que os machos. View this article in BioOne