Hoverflies, also calledflower flies orsyrphids, make up theinsectfamilySyrphidae. As theircommon name suggests, they are often seenhovering or nectaring atflowers; the adults of manyspecies feed mainly onnectar andpollen, while thelarvae (maggots) eat a wide range of foods. In some species, the larvae aresaprotrophs, specificallydetritivores,[1] eating decaying plant and animal matter in the soil or in ponds and streams. In other species, the larvae areinsectivores, preying onaphids,thrips, and other plant-sucking insects.
Insects such asaphids are consideredcroppests, so the aphid-eating larvae of some hoverflies are economically and ecologically important. The larvae are potential agents for use inbiological control, while the adults arepollinators.
About 6,000 species in 200genera have been described. Hoverflies are common throughout the world and can be found on all continents exceptAntarctica. Hoverflies are harmless to mostmammals, though many species aremimics of stingingwasps andbees, a mimicry which may serve to ward off predators.
Hoverfly hovering behavior is unlike that ofhummingbirds since they do not feed in midair. Hovering in general may be a means of finding a food source. Male hovering is often a territorial display while seeking females,[2]while female hovering serves to inspectovipositing sites.[3][4][5]
Adult hoverflies often hover over the plants they visit
The size of hoverflies varies depending on the species.[6] For exampleParagus tibialis[7][8][9] is 3–5 mm (1⁄8–13⁄64 in) long, whileCriorhina nigriventris is13.6–20.6 mm (17⁄32–13⁄16 in) long.[10] Some, such as members of the genusBaccha, are small, elongated, and slender, while others, such as members ofCriorhina, are large, hairy, and yellow and black. As members of theDiptera, all hoverflies have a single functional pair of wings, with the hind wings reduced tobalancing organs.[11] Many species are brightly colored, with spots, stripes, and bands of yellow or brown covering their bodies.[11] Due to this coloration, they are often mistaken both by insect-eating birds and by humans forwasps orbees; they exhibitBatesian mimicry. Despite this, hoverflies are harmless to humans.[6] Drone flies,Eristalis tenax, resemble honeybees, an example of Batesian mimicry.[12]
With a few exceptions,[13] Hoverflies are distinguished from other flies by having aspurious vein, located parallel to their fourth longitudinal wing vein.[6] Adults feed mainly onnectar andpollen.[11] Many species also hover around flowers, lending to their common name.[6]
Bee flies of the familyBombyliidae often mimicHymenoptera and hover around flowers, as well, rendering some bombyliid species hard to tell apart from Syrphidae at first glance. Hoverflies can, nevertheless, be distinguished in the field by anatomical features such as:[citation needed]
The legs and mouthparts of hoverflies are usually not particularly long and thin (some bombyliids have a long and needle-like proboscis, many have legs that are noticeably longer and thinner than in similar-sized syrphids)
Their facial cuticle often has prominent bulges and/or beak- to knob-like projections (most bee flies have an evenly curved or sloping face).
The wings are often clear or have smooth gradients of tinting, and their veins merge posteriorly into a "false edge" that runs parallel to the wing's true rear edge and extends along half or more of the wing length (bombyliid wings lack a "false rear edge" and often have large dark areas with sharp boundaries, or complex patterns of spots).
Their abdomens and thoraces often have glossy cuticular body surfaces, abdominal colors are usually mainly due to cuticular pigments (bee flies are usually very hairy, their abdominal colors are almost always due to pigmentation of hairs and not the underlying cuticle).
Their wariness of people is surprisingly low, and their behaviour can be observed up close.
Unlike adults, themaggots of hoverflies feed on a variety of foods. Some aresaprotrophs, eating decaying plant or animal matter, while others areinsectivores, eatingaphids,thrips, and other plant-sucking insects.[6][14] Predatory species are beneficial to farmers and gardeners, because aphids destroy crops, and hoverfly maggots are often used inbiological control. That includes one of the most common widespread hoverfly species,Episyrphus balteatus, the larvae of which feed on aphids.[citation needed]
An example of a well-known hoverfly maggot is therat-tailed maggot of thedrone fly,Eristalis tenax. It has a breathing siphon at its rear end, giving it its name.[6] The species lives in stagnant water, such as sewage and lagoons.[15] The maggots also have a commercial use, and are sometimes sold forice fishing.[16]
Very rarely, hoverfly larvae have causedaccidental myiasis in humans. That occurs when the larvae are accidentally ingested from contaminated food.[15][17]
While some hoverfly larvae are aquatic and are often found in stagnant water, those of species that prey uponaphids and other plant parasites are usually terrestrial, residing on leaves.[22] Adults are often found near flowers, their principal food source being nectar and pollen.[11] Some species areinquilines; for instance, members of the genusVolucella can be found in bumblebee nests, while members ofMicrodon aremyrmecophiles, found in ant or termite nests.[6] Others can be found in decomposing vegetation.[citation needed]
Hoverflies are importantpollinators of flowering plants in many ecosystems worldwide.[23] Syrphid flies are frequent flower visitors to a wide range of wild plants, as well as agricultural crops, and are often considered the second-most important group of pollinators after wildbees. Relatively little research into fly pollinators has been conducted, compared to bees.[23] Bees are thought to be able to carry a greater volume of pollen on their bodies, but flies may be able to compensate for this by making a greater number of flower visits.[citation needed]
Like many pollinator groups, syrphid flies range from species that take ageneralist approach to foraging by visiting a wide range of plant species through those that specialize in a narrow range of plants.[24] Although hoverflies are often considered mainly nonselective pollinators, some hoverflies species are highly selective and carry pollen from one plant species.[25]Cheilosia albitarsis is thought to only visitRanunculus repens.[citation needed]
Specific flower preferences differ among species, but syrphid fly species have repeatedly been shown to prefer white- and yellow-coloured flowers.[26] Nonvisual flower cues such as olfactory cues also help these flies to find flowers, especially those that are not yellow.[27] Many syrphid fly species have short, unspecialized mouth parts and tend to feed on flowers that are more open as the nectar and pollen can be easily accessed.[28]
Also, a number of interactions occur between orchids and hoverflies. The orchid speciesEpipactis veratrifolia mimics alarmpheromones of aphids which attracts pollinating hoverflies.[29] Another plant, theslipper orchid in southwest China, also achieves pollination by deceit by exploiting the innate yellow color preference of syrphids.[30]
Fredrik Sjöberg's [sv] bookThe Fly Trap concerns his enthusiasm for hoverflies on the island ofRunmarö in theBaltic Sea.[35] The island is a hotspot for hoverflies and other insects; Sjöberg has collected 58 species of butterflies there, and (in seven years of hunting) 202 species of hoverflies, including 180 in his garden.[36]
Skevington, J.H., et al., 2019. Field Guide to the Flower Flies of Northeastern North America. Princeton University PressISBN9780691189406. This book "covers all 413 known syrphid species that occur in or north of Virginia, Kentucky, and Missouri, west to include Iowa, Minnesota, Ontario, and Nunavut, and east to the Atlantic Ocean, including Greenland."
Stubbs, A.E. and Falk, S.J. (2002)British Hoverflies An Illustrated Identification Guide. Pub. 1983 with 469 pages, 12 col plates, b/w illus. British Entomological and Natural History SocietyISBN1-899935-05-3. 276 species are described with extensive keys to aid identification. It displays 190 species on colour plates. 2nd edition, pub. 2002, includes new British species and name changes. It includes European species likely to appear in Britain. Additional black and white plates illustrate the male genitalia of the difficult generaCheilosia andSphaerophoria.
van Veen, M.P. (2004)Hoverflies of Northwest Europe: Identification Keys to the Syrphidae. KNNV Publishing, UtrechtISBN9050111998.
Miranda G.F.G., Young A.D., Locke M.M., Marshall S.A., Skevington J.H., Thompson F.C. (2013) Key to the Genera of Nearctic Syrphidae.doi:10.3752/cjai.2013.23
Bot, S. and Van de Meutter, F. (2023)Hoverflies of Britain and North-west Europe: A photographic guide (Bloomsbury Naturalist).ISBN978-1-3994-0245-3.
^Ball, S.G.; Morris, R.K.A. (2000).Provisional atlas of British hoverflies (Diptera, Syrphidae).Monks Wood, UK: Biological Record Centre. pp. 167 pages.ISBN1-870393-54-6.
^Van Veen, M.P. (2004).Hoverflies of Northwest Europe, Identification Keys to the Syrphidae (Hardback). Utrecht: KNNV Publishing. p. 254.ISBN90-5011-199-8.
^Skevington, Jeffrey H. (2019).Field Guide to the Flower Flies of Northeastern North America. Princeton University Press.ISBN9780691189406.
^abLarson, B.M.H.; Kevan, P.G.; Inouye, D. W. (2001). "Flies and flowers: taxonomic diversity of anthophiles and pollinators".Canadian Entomologist.133 (4):439–465.doi:10.4039/ent133439-4.S2CID55767580.
^Sajjad, Asif; Saeed, Shafqat (2010). "Floral host plant range of syrphid flies (Syrphidae: Diptera) under natural conditions in southern punjab, Pakistan".Pakistan Journal of Biology.42 (2):1187–1200.
^Campbell, Alistair, J.; Biesmeijer, J. C.; Varma, V.; Wakers, F. L. (2012). "Realising multiple ecosystem services based on the response of three beneficial insect groups to floral traits and trait diversity".Basic and Applied Ecology.13 (4):363–370.Bibcode:2012BApEc..13..363C.doi:10.1016/j.baae.2012.04.003.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Rodriguez-Saona, C., Kaplan, I., Braasch, J., Chinnasamy, D., & Williams, L. (2011). Field responses of predaceous arthropods to methyl salicylate: A meta-analysis and case study in cranberries. Biological Control, 59(2), 394–303.https://doi.org/10.1016/j.biocontrol.2011.06.017
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