The Bombyliidae are a family of flies. Their common name is bee flies. Adults generally feed on nectar and pollen, some being important pollinators. Larvae generally are parasitoids of other insects. The Bombyliidae are a large family of flies comprising hundreds of genera, but the life cycles of most species are known poorly, or not at all. They range in size from very small (2 mm in length) to very large for flies (wingspan of some 40 mm). When at rest, many species hold their wings at a characteristic "swept back" angle. Adults generally feed on nectar and pollen, some being important pollinators, often with spectacularly long proboscises adapted to plants such as Lapeirousia species with very long, narrow floral tubes. Many Bombyliidae superficially resemble bees and accordingly the prevalent common name for a member of the family is bee fly. Possibly the resemblance is aposematic, affording the adults some protection from predators.
In parts of East Anglia locals refer to them as 'beewhals', in reference to their lance-like proboscises.
The larval stages are predators or parasitoids of the eggs and larvae of other insects. The adult females usually deposit eggs in the vicinity of possible hosts, quite often in the burrows of beetles or wasps/solitary bees. Although insect parasitoids usually are fairly host-specific, often highly host-specific, some Bombyliidae are opportunistic and will attack a variety of hosts.
While the Bombyliidae include a large number of species in great variety, most species do not often appear in abundance, and for its size this is one of the most poorly known families of insects. There are at least 4,500 described species, and certainly thousands yet to be described.