Hoverflies, also called flower flies or syrphids, make up the insect family Syrphidae. As their common name suggests, they are often seen hovering, maintaining a spot in the air as part of their display behavior; the adults of many species feed mainly on nectar and pollen, while the larvae (maggots) eat a wide range of foods. In some species, the larvae are saprotrophs, specifically detritivores, eating decaying plant and animal matter in the soil or in ponds and streams. In other species, the larvae are insectivores, preying on aphids, thrips, and other plant-sucking insects.

Insects such as aphids are considered crop pests, so the aphid-eating larvae of some hoverflies are economically and ecologically important. The larvae are potential agents for use in biological control, while the adults are pollinators.

About 6,000 species in 200 genera have been described. Hoverflies are common throughout the world and can be found on all continents except Antarctica. Hoverflies are harmless to most mammals, though many species are mimics of stinging wasps and bees, a mimicry which may serve to ward off predators.

Hoverfly hovering behavior is unlike that of hummingbirds 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,

while female hovering serves to inspect ovipositing sites.

<gallery mode="packed" heights="160px" widths="160px" caption="Adult hoverflies often hover over the plants they visit">

Eupeodes_fumipennis-female_hovering.jpg|Eupeodes fumipennis

Eupeodes_volucris-female_hovering.jpg|Eupeodes volucris

Helophilus_fasciatus-female_hovering.jpg|Helophilus fasciatus

Syritta_pipiens-male_hovering.jpg|Syritta pipiens

File:Syrphidae - kanagawa japan - 2023 11 9.ogv|A hoverfly on flowers in Japan

File:Purple bromeliad fly.webm|thumbtime=60|A purple bromeliad fly visiting Paris daisy, variety Madeira deep pink. Last scene is repeated at one fourth speed

File:Female Eristalis tenax.webm|thumbtime=121|A female common drone fly on Zinnia. A portion shown in close-up played at one-tenth place

File:Female Western Calligrapher.webm|thumbtime=181|Female Western Calligrapher on zinnia taking pollen and nectar. Insert shows entire visit at 3X speed. Some portions of main video shown at one-tenth speed

File:Female Margined calligrapher.webm|thumbtime=38|Female margined calligrapher fly consuming pollen from zinnia florets. A portion shown at one-tenth speed

</gallery>

Description

The size of hoverflies varies depending on the species. For example Paragus tibialis is long, while Criorhina nigriventris is long. Some, such as members of the genus Baccha, are small, elongated, and slender, while others, such as members of Criorhina, are large, hairy, and yellow and black. As members of the Diptera, all hoverflies have a single functional pair of wings, with the hind wings reduced to balancing organs. Many species are brightly colored, with spots, stripes, and bands of yellow or brown covering their bodies.

With a few exceptions, Hoverflies are distinguished from other flies by having a spurious vein, located parallel to their fourth longitudinal wing vein. Predatory species are beneficial to farmers and gardeners, because aphids destroy crops, and hoverfly maggots are often used in biological control. That includes one of the most common widespread hoverfly species, Episyrphus balteatus, the larvae of which feed on aphids.

thumb|right|Hoverfly depositing egg on [[Epipactis helleborine which has ants farming aphids]]

An example of a well-known hoverfly maggot is the rat-tailed maggot of the drone fly, Eristalis tenax. It has a breathing siphon at its rear end, giving it its name. The maggots also have a commercial use, and are sometimes sold for ice fishing.

thumb|right|[[Ichneumonidae|An ichneumonid wasp ovipositing inside a hoverfly larva]]

Very rarely, hoverfly larvae have caused accidental myiasis in humans. That occurs when the larvae are accidentally ingested from contaminated food.

Evolution

The oldest known fossils of crown group Syrphidae are from the Eocene aged Florissant Formation, Green River Formation and Baltic amber. The genus Prosyrphus, found in Late Cretaceous (Cenomanian) Burmese amber, appears to represent a stem group to the family.

Distribution and habitat

Hoverflies are a cosmopolitan family found in most biomes, except extreme deserts, tundra at extremely high latitudes, and Antarctica. Certain species are more common in certain areas than others; for example, the American hoverfly, Eupeodes americanus, is common in the Nearctic realm, and the common hoverfly, Melangyna viridiceps, is common in the Australasian realm. About 6,000 species and 200 genera are in the family.

While some hoverfly larvae are aquatic and are often found in stagnant water, those of species that prey upon aphids and other plant parasites are usually terrestrial, residing on leaves. Adults are often found near flowers, their principal food source being nectar and pollen. 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 wild bees. Relatively little research into fly pollinators has been conducted, compared to bees. Although hoverflies are often considered mainly nonselective pollinators, some hoverflies species are highly selective and carry pollen from one plant species. Cheilosia albitarsis is thought to only visit Ranunculus repens.

Specific flower preferences differ among species, but syrphid fly species have repeatedly been shown to prefer white- and yellow-coloured flowers. Nonvisual flower cues such as olfactory cues also help these flies to find flowers, especially those that are not yellow. 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.

Also, a number of interactions occur between orchids and hoverflies. The orchid species Epipactis veratrifolia mimics alarm pheromones of aphids which attracts pollinating hoverflies. Another plant, the slipper orchid in southwest China, also achieves pollination by deceit by exploiting the innate yellow color preference of syrphids.

Systematics

Relationship with humans

thumb|Hoverfly nectaring on a small flower bud covered with dew drops.

Hoverflies (adult syrphid flies) are pollinators.

Larvae of many hoverfly species prey upon pest insects, including aphids and leafhoppers, which spread some diseases such as curly top, so they are seen in biocontrol as a natural means of reducing levels of pests. Gardeners, therefore, sometimes use companion plants to attract hoverflies. Those reputed to do so include Alyssum spp., Iberis umbellata, statice, buckwheat, chamomile, parsley, and yarrow. Many syrphids, such as Toxomerus marginatus, are attracted to herbivore-induced plant volatiles, and there are commercial formulations of said volatiles, like methyl salicylate, which can be used to attract them for biocontrol purposes. Larvae in the subfamily Eristalinae live in semi-aquatic and aquatic environments, including manure and compost, and can filter and purify water.

book The Fly Trap concerns his enthusiasm for hoverflies on the island of Runmarö in the Baltic Sea. 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.

Identification guides

  • Skevington, J.H., et al., 2019. Field Guide to the Flower Flies of Northeastern North America. Princeton University Press . 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 Society . 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 genera Cheilosia and Sphaerophoria.
  • van Veen, M.P. (2004) Hoverflies of Northwest Europe: Identification Keys to the Syrphidae. KNNV Publishing, Utrecht .
  • 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.
  • Bot, S. and Van de Meutter, F. (2023) Hoverflies of Britain and North-west Europe: A photographic guide (Bloomsbury Naturalist). .

Regional lists

  • List of hoverfly species of Great Britain
  • List of the Syrphidae of Ireland
  • List of flower flies of New Zealand
  • List of the flower flies of North America
  • Syrphidae of New York State

References

  • Hoverfly – index to scholarly articles
  • All About Hoverflies
  • A website about Dutch hoverflies
  • Hoverfly Recording Scheme – UK Dipterists Forum
  • world Syrphidae checklist, including relationship with other taxa.
  • Diptera.info Picture Gallery

Species lists

  • Nearctic at nearctica.com
  • West Palaearctic including Russia at faunaeur.org
  • Australasian/Oceanian at bishopmuseum.org
  • List of the flower flies of North America
  • List of hoverfly species of Great Britain
  • Syrphidae of New York State
  • List of flower flies of New Zealand