Female horse-flies require blood to help produce eggs whereas males feed on nectar from flowers. Horse-flies lay their eggs in the mud of river banks or in damp earth. The larvae hatch and some are predatory, feeding on the grubs of other mud-dwelling insects. They can paralyse their prey by injecting them with venom, which also pre-digests the grub allowing the horse-fly larva to suck their victim dry. The larvae pupate just below the surface, and over-winter in this state. The adult flies emerge through small holes in the mud in May, and are on the wing until September.