Bombyliidae

The Bombyliidae are a family of flies, commonly known as bee flies. Some are colloquially known as bomber flies. Adults generally feed on nectar and pollen, some being important pollinators. Larvae are mostly parasitoids of other insects.

The Bombyliidae are a large family of flies comprising hundreds of genera, but the life cycles of most species are poorly known, or not at all. Their size varies between species ranging from 2 mm long to a 40 mm wingspan making them some of the largest flies. 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. Unlike butterflies, bee flies hold their proboscis straight, and cannot retract it. Many Bombyliidae superficially resemble bees and accordingly the prevalent common name for a member of the family is bee fly. Possibly the resemblance is Batesian mimicry, affording the adults some protection from predators.

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, wasps, or solitary bees. Although insect parasitoids are usually fairly, often highly, host-specific, some Bombyliidae are opportunistic and will attack a variety of hosts.

The Bombyliidae include at least 4,500 described species, and certainly thousands more remain to be described. However, most species do not often appear in abundance, and compared to other major groups of pollinators they are much less likely to visit flowering plants in urban parks or suburban gardens. As a result, this is arguably one of the most poorly known families of insects relative to its species richness.^{[citation needed]} The family has a patchy fossil record, with species being known from a handful of localities, the oldest known species are known from the Middle Cretaceous Burmese amber, around 99 million years old.

Although the morphology of beeflies varies in detail, adults of most bee flies are characterized by some morphological details that make recognition easy. The dimensions of the body vary, depending on the species, from 1.0 mm to 2.5 cm. The form is often compact and the integument is usually covered with dense and abundant hair. The coloration is usually inconspicuous and colours such as brown, blackish- grey, and light colors like white or yellow predominate. Many species are mimics of apoid Hymenoptera. In other species patches of flattened hairs occur that can act as silvery, gilded or copper-tone reflecting mirrors; these perhaps serve as visual signals in conspecific mate/rival recognition, or perhaps imitate reflecting surface particles on bare soils with high content of materials like quartz, mica or pyrite.

The head is round, with a convex face, often holoptic in males. The antennae are of the type aristate composed of three to six segments, with the third segment larger than the others; the stylus is absent (antenna of three segments) or is composed of one to three flagellomeres (antenna of four to six segments). The mouthparts are modified for sucking and adapted for feeding on flowers. The length varies considerably: for example, the Anthracinae have short mouthparts, with the labium terminating in a large fleshy labellum; in Phthiriinae, the tube is considerably longer, and in Bombyliinae more than four times the length of the head.

The legs are long and thin and the front legs are sometimes smaller and more slender than the middle and rear legs. Typically, they are provided with bristles at the apex of the tibiae, without empodia and, sometimes, also without pulvilli. The wings are transparent, often hyaline or evenly colored or with bands. The alula are well developed and in the rest position the wings are kept open and horizontal in a V shape revealing the sides of the abdomen.

The abdomen is generally short and wide, subglobose-shaped, cylindrical, or conical, composed of six to eight apparent urites. The remaining urites are part of the structure of the external genitalia. The abdomen of the females often ends with spinous processes, used in ovideposition. In Anthracinae and Bombyliinae, a diverticulum is present in the eighth urite, in which the eggs are mixed with sand before being deposited.