The insect Gregor Mendel bred in his later heredity experiments was the bee.
After his famous pea-plant studies, Mendel continued investigating inheritance in other organisms. At the Augustinian monastery in Brno, he kept specially designed beehives and bred honeybees. Historical accounts identify the bees as Cyprian and Carniolan varieties, both known for being particularly aggressive.
Mendel hoped that bees might help him explore heredity beyond plants, but the work did not produce a surviving body of experimental results. Only brief references to his beekeeping appeared in reports of the Moravian Apiculture Society. The bees reportedly became a nuisance to monks and visitors, and Mendel was eventually asked to remove them.
The answer is sometimes confused with mice because later colleagues recalled that Mendel may also have bred mice of different sizes. However, the insect associated with his later experiments was bees. His bee studies never achieved the lasting clarity of his pea research.