B. major has several host species, including the brood of solitary wasps and bees, particularly digging bees such as Andrena. Egg deposition takes place by the female hovering above the entrance of a host insect nest, usually a solitary bee, and throwing down her eggs using a flicking movement.Boesi, R., Polidori, C. and Andrietti, F. 2009 — Searching for the Right Target: Oviposition and Feeding Behavior in Bombylius Bee Flies (Diptera:Bombyliidae).Zool. Stud., 48:141-150. The larvae are hypermetamorphic parasitoids which then feed on the food stored, as well as the young solitary bees or wasps. If the female is unable to flick her eggs near the nest, she plants them on flowers visited by the host insects. The developing larvae then make their way to the host nest or attach themselves to the bees or wasps to then be carried to the nest.
