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''Bombylius major'' (commonly named the large bee-fly, the dark-edged bee-fly or the greater bee fly) 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
bumblebee A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only Extant taxon, extant group in the tribe Bombini, though a few extinct r ...
s 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 ''Bombylius'' is a large genus of flies belonging to the family Bombyliidae. They are known as the bee-flies, due to their striking resemblance to bees and bumblebees, and are distributed worldwide. One species of the genus, '' Bombylius major'', ...
'' currently comprises around 450 described species. ''Bombylius major'' can be found from April to June throughout
temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
,
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
and some parts of
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
, 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 Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
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.''Insects'' , Collins Gem , Guide, 1986, page 114, 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 (bees have two), 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 Holometabolism, also called complete metamorphosis, is a form of insect development which includes four life stages: egg, larva, pupa, and imago (or adult). Holometabolism is a synapomorphic trait of all insects in the clade Holometabola. Immatur ...
. ''Bombylius major'' has several host species, including the brood of solitary wasps and bees, particularly digging bees such as ''
Andrena ''Andrena'' is a genus of bees in the family Andrenidae. With over 1,500 species, it is one of the largest genera of animals. It is a strongly Monophyly, monophyletic group that is difficult to split into more manageable divisions; currently, '' ...
''. 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 Hypermetamorphosis, or heteromorphosis, is a term used mainly in entomology; it refers to a class of variants of holometabolism, that is to say, complete insect metamorphosis. Hypermetamorphosis is exceptional in that some instars, usually larva ...
parasitoids In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...
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 ''Claytonia virginica'', the Virginia springbeauty, eastern spring beauty, grass-flower narrowleaf springbeauty or fairy spud, is an herbaceous perennial plant in the family Montiaceae. Its native range is eastern North America. Its scientific na ...
, 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 (and almost exclusively) 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.


Female

In Russia, female ''B. major'' act in a narrow oligophagous manner, favoring a limited number of food sources, including pollen grains of Siberian squill ('' Scilla siberica''), lesser celandine (''
Ficaria verna ''Ficaria verna'' (formerly ''Ranunculus ficaria'' ), commonly known as lesser celandine or pilewort, is a low-growing, hairless perennial flowering plant in the buttercup family Ranunculaceae. It has fleshy dark green, heart-shaped leaves and d ...
''), and willow (''
Salix caprea ''Salix caprea'', known as goat willow, pussy willow or great sallow, is a common species of willow native to Europe and western and central Asia.Meikle, R. D. (1984). ''Willows and Poplars of Great Britain and Ireland''. BSBI Handbook 4. . De ...
'') over dandelion (''
Taraxacum officinale ''Taraxacum officinale'', the dandelion or common dandelion, is a herbaceous perennial flowering plant in the daisy family, Asteraceae. The common dandelion is well known for its yellow flower heads that turn into round balls of many silver-tuf ...
''), coltsfoot (''
Tussilago farfara ''Tussilago farfara'', commonly known as coltsfoot, is a plant in the tribe Senecioneae in the family Asteraceae, native to Europe and parts of western and central Asia. The name "tussilago" is derived from the Latin ''tussis'', meaning cough, an ...
''), and primrose (''
Primula vulgaris ''Primula vulgaris'', also called the common primrose, is a species of flowering plant in the family (biology), family Primulaceae, native plant, native to Eurasia.''Flora Europaea'Primula vulgaris''/ref> The common name of this plant is prim ...
'').


Male

In the same study, male ''B. major'' preferred plants similar to females, with the exception of dandelion. However, an examination of the gut showed a regularly lower amount of pollen than in females. Males consistently consume less quantities of pollen than females. Ingestion of pollen differs throughout a male life cycle, with more pollen being consumed in towards earlier stages. Overall, males had a preference for nectar and fed on significantly greater portions of nectar over pollen.


Behavior

There is continued research on the behavior of ''B. major'' in respect to environmental factors, mating, and human interaction.


Flight

It has been discovered that the fly is capable of a unique type of flight behavior, which was discovered with the use of a high speed camera. In this behavior, the flies are seen to rotate around a vertical axis as they fly (this action is known as “yawing”). However, it is still unknown what can cause this behavior to be triggered and what purpose it serves, but a proposed explanation includes mating habits.


Pollinator role

The ''B. major'' bee-fly is a common, generalist floral pollinator, meaning that it does not give preference to one flower over another, instead pollinating a wide variety of plant families and species. The fly uses its proboscis to carry and transfer the pollen. The species is a dominant pollinator within its community, sometimes even pollinating up to two thirds of the local flowers. In addition, ''B. major'' will visit and pollinate plants that attract few other species. Some types of flowers, for example ''
Pulmonaria officinalis ''Pulmonaria officinalis'', common names lungwort, common lungwort, Mary's tears or Our Lady's milk drops, is a herbaceous rhizomatous evergreen perennial plant of the genus '' Pulmonaria'', belonging to the family Boraginaceae. Etymology The g ...
,'' will be almost exclusively pollinated by ''B. major'', with other species contributing a negligible amount to that plants pollination. Some flower species, such as '' Delphinium tricorne'', are even specifically adapted to the fly in terms of color, shape, and form. If given the choice, ''B. major'' will have a consistency in plant choice.


Flower attraction

Long distance floral attraction is governed by optical sense, with color being the most important factor. The flies are typically more attracted to blue and violet colors, and occasionally yellow, over orange and pink. However, short distance floral attraction is based on the fly's olfactory sense.


Activity

The fly is mostly active during day hours when the weather conditions are warm and sunny. ''B. major'' is attracted to sunnier places and is more likely to pollinate these areas, with a larger average of flower visits in areas of higher amounts of sunshine. The fly will hide in the trees during the night and usually dart away from a cast shadow.


References

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External links

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Photograph by Felipe vilarroya
{{Taxonbar, from=Q1549111 Bombyliidae Asilomorph flies of Europe Diptera of Asia Diptera of North America Insects of the United States Flies described in 1758 Taxa named by Carl Linnaeus Articles containing video clips Parasites of bees