Two microsporidian species, Nosema apis and Nosema ceranae, infect honey bees (Apis mellifera) worldwide. They are obligate intracellular parasites that multiply in the epithelial lining of the bee’s midgut and cause nosemosis. N. ceranae infections were primarily found in Apis cerana and raised interest in the last decade with the discovery of their presence in the European honey bee (Apis mellifera). Nosema spp. utilizes hosts’ energetic reserves for the purpose of propagation and disrupts the digestive processes of the bee. Nosemosis reduces the lifespan of a single bee and affects the performance of the colony. It also has an economic impact through the reduction in the honey and pollen yield of severely infected colonies or even causes them to collapse. Lack of effective therapy for nosemosis is of special concern and calls for scientific attention. Although N. ceranae and N. apis are similar in many aspects, there are important differences between them such as clinical signs of infection or the ability to resist low temperatures.