Ophryocystis is a genus of neogregarine protozoan parasites that infect insects in the orders Coleoptera and Lepidoptera. Ophryocystis species with beetle hosts replicate in the Malpighian tubules, while those infecting butterflies do so in the hypodermis.
There are currently 16 described Ophryocystis species. The most well known and extensively studied is Ophryocystis elektroscirrha, which infects Danaus (monarch and queen) butterflies.