Phenotypic plasticity is the capacity of a single genotype to exhibit a range of phenotypes in response to environmental variation. For a parasite, different hosts represent different environments. The septate gregarine parasite Leidyana subramanii (Apicomplexa: Eugregarinorida) can infect at least 17 species of grasshopper. To determine if L. subramanii exhibited host-induced phenotypic plasticity, we cultured this gregarine species in 2 different grasshopper hosts (Eyprepocnemis alacris alacris and Poekilocerus pictus). Our results indicated that host species dramatically influenced L. subramanii morphology. When reared in E. a. alacris, the gamonts of L. subramanii were 5 times longer and wider than when reared in P. pictus. The smaller size of the parasite when reared in P. pictus may be influenced by the grasshopper's unique diet and chemical defenses. Poekilocerus pictus feeds on toxic milkweeds (Calotropis spp.) and sequesters plant cardenolides in its tissues. These plant-derived compounds may influence growth and development of the parasite. Our findings indicate that gregarines can exhibit phenotypic plasticity. Such plasticity is seldom discussed in the scientific literature, despite the fact that parasite intraspecific variability, including phenotypic plasticity, can confuse species identification and confound remediation. As such, these data indicate that parasitologists studying gregarines need to be aware of intraspecific variation in their study organisms.