Bombylius major
Bombylius major is a parasitic bee mimic fly. B. major is the most common type of fly within the Bombylius genus. The fly derives its name from its close resemblance to bumblebees and is often mistaken for them.
Bombylius major exhibits a unique flight behavior known as "yawing" and plays a role in general pollination, without preference of flower types. The fly does not bite, sting, or spread disease. However, the fly uses this mimicry of bumblebees to its own advantage, allowing close access to host solitary bee and wasp nests in order to deposit its eggs. After hatching, the larvae find their way into the nests to parasitically feed on the grubs.
Description
Bombylius major is part of the family Bombyliidae, with a reported 6000 species worldwide. The subfamily Bombyliinae contains approximately 1100 identified species. The genus Bombylius currently comprises around 450 described species.Bombylius major can be found from April to June throughout temperate Europe, North America and some parts of Asia, concentrated in the northern hemisphere. The species occurs across a variety of environments, from arid to moist.
Morphology
The adult body size varies from 6.3 to 12 mm in length and is considered a relatively medium-sized fly. The body color is dark, but is densely covered by a thick coat of lighter color hairs. The head is typically brown and black hairs, but the lower portion of the head is mostly white hairs. It has dark patches on the anterior half of the wings and long hairy legs that dangle while in flight. The dark wing span can range from 8.4 to 14 mm and has a dark brown edge. Their boldly patterned wings have a distinct dividing border through the horizontal middle between the dark and clear portions. Their antennae are typically very short and pointed. Additionally, the species has long legs and a long rigid proboscis found in the front of the head, which is used to feed on the nectar of flowers. The proboscis ranges from 5.5 to 7.5 mm in length. While its wings continue to beat, its front legs grip the flower and its long rigid beak is inserted to collect the nectar. Despite its fearsome appearance, the beak is quite harmless. Males are typically smaller than females. Movement is categorized by both hovering and darting between locations. The flies also emit a high-pitched buzz.Mimicry
The species gets its common name from its similarity in appearance to bees. This mimicry likely confers some defense against predation. However, there are several distinguishing features: B. major has only one pair of wings, extremely thin legs, and the head is very small, with a long rigid proboscis.Life cycle
Bombylius major is mostly seen in the spring, beginning to appear at the end of March and large numbers seen until the end of May, with the species being sighted into June. The fly is holometabolous.Bombylius 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. 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.
Egg
The parasitic eggs of B. major are produced in large numbers, however few will make it to the host insect burrow entrance. The female fly will dip down and coat her rear abdomen with dust that covers the eggs as they leave the female.Larvae
Larvae live parasitically in the nests of various solitary bees and wasps. When the fly larva locates a host larva, it will consume it slowly, greatly increasing in size as it tightly holds onto the host, eventually becoming a pupa and overwintering.Pupae
White larvae gradually turn into a yellowish brown pupa, with distinct mouthparts, wings, antennae, and legs.Diet
The species sometimes acts as a nectar robber, sometimes as a pollinator; this foraging behavior allows the species to feed on floral nectar, which is an essential part of adult fly diets. This is facilitated by the characteristic long proboscis of the fly, which is horizontally inserted into the flower. This occurs as the fly continues to buzz in the air, sometimes without touching either the anthers or stigma of the flower. However, in some plant species such as Claytonia virginica, bee flies can be effective pollinators. The fly also consumes pollen as part of its diet, with considerable differences between the sexes. Males and females visit the same range of flowers as a food source.Along with one other species, Bombylius pygmaeus, B. major was observed to selectively visit bluets at several North American sites despite the abundant presence of many other flowers. Of the other pollinators present, these flies were also the most frequent visitors to the flowers.