All About Hover Flies

CV Duke, BSc (Hons)

Images by Leon Truscott, David Iliff, Chris Webster, David Skingsley

(C) All Rights Reserved 2006
 

What Are Hover Flies?

Hover Flies ( known in America as Flower Flies ) belong to a large family of small to big flies. They are true flies or Diptera, with only one pair of wings in the Family Syrphidae. ( Wasps and bees have two pairs ).

Hoverflies have spots, bands or stripes, of yellow, brown against a dark-coloured background, sometimes with dense hair covering the body surface (emulating furry bumble bees). Their fast flight, motionless flight and, in some species, their size are astonishing feats. Some Hovers are among the biggest flies of Central Europe. Many species are very colorful. It is not always that easy to identify hover flies. Some thick-headed flies and bee flies are similar and dark coloration makes it hard to identify them correctly at a glance. Bee flies tend to be longer hairy, have snouts and are a study in themselves!

Hovering is a speciality although other flies can also hover - the head of the insect remains absolutely still whilst in flight. They may be seen "Nectaring" on many wild and garden flowers where they are amongst the most frquent of visitors. In Holland and Belgium alone over 300 species exist!. In Britain About 270 species are known at present, but significant species and numbers can migrate like butterflies with powerful flight such as the Red admiral or Painted lady.The Marmalade Fly Episyrphus balteatus is one of the most common hoverflies to be seen in the garden. The distinctive double stripes on the abdomen make it almost unmistakable.

Many are seen in the summer season in number mixing with butterflies, bees, bumble bees and other flower dependent insects. Male Hovers tend to enmerege and mature first, earlier in the season to ensure reproduction is sucessful. Many species are useful to the gardener since their larvae eat pest aphids on garden plants and crops.The degree to which they contribute to pollination is also ironically poorly investigated but no doubt are important for Carrot, Onion and fruit Trees.

This group is a useful indicator for evaluating site ecology, being a day active, with a varied range of larval habitat specialisations

 

Table 1 General Classification of the Family: Syphidae

  Sub-Family: Syriphinae

  Genera

      Tribe Syrphini Eg Syrphus, Epistophe, Scaevia

      Tribe Bacchini Eg Bacchus, Melastoma, Platycheirus

   Sub-Family: Eristalinae

  Genera

      Tribe Cheilosiini Eg: Ferdinandea, Rhingia, Cheilosa

      Tribe Chrysogasterini Eg: Chrysogaster, Neoascia

      Tribe Volucellini Eg Volucella

      Tribe Sericomyiini Eg Sericomyia

      Tribe Xylotini Eg Syrittia, Xylota

      Tribe Eumerini Eg Merodon

      Tribe Eristinali Eg Eristais, Helophilus, Myiatropa

   Sub-Family: Microdontinae

  Genera

        Rare in UK
 

What is the purpose of the Bright bodies and patterns?

Many of the of hoverflies have ornate body patterns, often of black and yellow, to mimic wasps and bees but are harmless. Hover fly mimicry include warning coloration of yellow and black, a narrow waist like a wasp and even the ability to mimic the stinging action of a wasp, by pushing the tip of the abdomen into your fingers if they are caught and held.

The superficial resemblances (a) to honeybees (for example the genus Eristalis spp ), to (b) bumblebees (in the genera Pocota or Volucella) and to (c) wasps (in the genus Chrysotoxum) is often striking.

 

Fig 1 The Drone Fly Eristalis tenax (Left) & Honey Bee - Apis melifera (Right) feeding on everlasting Daisy

IMAGE WITH THANKS YVONNE (C) 2007

Fig 2. The Common Wasp ( paravespula vulgris ) Left compared to the Hover Fly Right (Chrysotoxum cautum - female)

IMAGES (C) COLIN DUKE 2007 (C) DAVID ILIFF 2007

Fig 3. The Bumblebee (Bombus ) Below Left compared to the Hover Fly Below Right (Volucella bombylans)

The Bumblee Bee The Hover Fly Volucella bombylans Male
IMAGES (C) COLIN DUKE 2007 (C) LEON TRUSCOTT2007

Comments

(a) In the Eristalis species there are more subtle varieties as they attempt to emulate the various form the honey bee takes Merodon equestris var naricisus, var equestris. There is some evidence to suggest that colour form depends on temperature exposure that larvae experience, with lighter forms appearing mid-summer and darker forms earlier in the year.

(b) Volucella bombylans var plumata imitates the Earth or Common garden Bumblebee. The Hover Fly larva of this species go one step further and actually live in the nests of bumble bees, eating the rubbish produced being both detritivores and larval predators. and possibly the bees larvae as well.( exception is V. inflata who live in aqueous insect messes)

(c) The genus Chrysotoxum admirable displays associated features,wasp like stripings, dark wings, resembling social wasps the antennae are long and wasp like, not seen in typically in many other flies. Fig 2. Another good but less common example is Doros profuges, a large hoverfly, the adult of which is a spectacular wasp-mimic

Some species wave their front legs in front of their face to mimic the jointed antennae of the potter wasps. It is thought that this mimicry protects hover flies from falling prey to birds and other insectivores which avoid eating true wasps because of their sting. Hover flies do not sting and are harmless.

This kind of Mimicry is know as Batesian mimicry involving a palatable, unprotected species (the mimic - Hoverfly ) that closely resembles an unpalatable or protected species (the model - The Bee or Wasp ). Birds know not to attack a bee as they will be stung. Gilbert (2004) Ref 11 further extends that Hoverflies also behaviourially mimic the patterns and habits of their hymenopteran models.

Clearly Hoverflies not only mimic the host but have developed elaborate evolutionary mechanisms to ensure the larva survive

What is the easy way to confirm if a Fly is a Hover?

Much information can be revealed by the wings - two in the case of Hoverflies as oposed to 4 in the Mimic - The Bees

Despite the rather random appearance of veination in hover flies a logical appraisal of characteristics can be applied based on veins that radiate outward - Radial veins, Median Veins and Anal Veins. The distinctive presence of the two cross veins in the Hover flies are described below.

Like many diptera looking at veination characteristics takes identification one stage further. To confirm an insect is a Hover one of the most characteristic features of hoverflies is the presence of a longitudinal false vein in the wing if an examination of wing veins is necessary. In Hovers a great part of the edge of the wing is without veins. The vein running all the way to the edge in most flies ( Radial), only reaches the last transverse vein, not the edge in hover flies upper outer cross vein (A) and lower outer cross vein. Another feature of hover flies is the so-calles 'floating vein' (B). This vein just ends nowhere. Usually veins end either at the edge of the wing or in another vein. Both these features being present means you are actually looking at a hover fly.

Generally the dorsal thorax does not have coarse bristles.

Looking at the behaviour of the Fly in air also confirms that it is a hover either by its characteristic controlled hovering or its rapid start stop darting.

Fig 4 Veination in the Hover Fly - the false or floating vein.

How Do I begin to identify the many Species?

Becoming familiar with Hoverfly Antomy will soon yield subtle features used to distinguish the many similar flies down to species as well as genera level. Using Keys will readily assist..It is beyond the scope of this article to list or describe the identification features in detail but the presence shape, size and colour of Bands and/or Bars, Presence or absence of hairs on anatomical parts, banding on the eyes are imoportant characteristics. Whether for example the Antenna is long, short,elongated or the Arista is Plumose (feathered) Colour of hairs on the Scutellum. The colour and shape of the face ( Flat Convex etc ). The angle of which the eyes are set to the frons and the relative positioning of the occelli to the front or rear on the head. Considerable attention is given to the "Veination" or pattens of veins on the wings

Gilbert Ref: 4 is an excellent intoduction to basic Hoverfly Identification. As expertise progressess the definitive works of Stubbs Ref: 1 is invaluable in narrowing down each species using the many keys available. The identification of Hoverfly Larvae in itself a study can be explored using an excellent guide on The Hoverfly Larva by Rotheray Ref: 5. The amateur naturalist may make very valuable contributions with report on for example distribution valuable to the Hover Fly Recording scheme Ref 5

Fig 5:Basic Features of The Hover Fly

Click on the Term To Find Out More

Glossary

Abdomen The last of 3 major components making up an insect containing digestive organs etc

Alula A memmbranous flap close to the squama

Antenna Composed of 3 segments with a hair like projection - the arista arising out of the third or final segment.

Arista - A bristle like structure arising out of the 3 segmented parts making up the antenna

Frons - The space behind the antenna between the eyes when viewed dorsally.

Haltere - Balance organs located to the mid thorax which act as a "gyroscope" to control flight.

Humerii - The raised corners to the front of the dorasal thorax

Ocelli - An arrangement of simple celled eyes usually in 3, on the top of head in a triangulated vertex.

Occiput The margin immediately behine the Compounbd Eyes

Postalar Cali - Elongated swellings at the posterior corners of the Thorax.

Pre Genital Segment. The end segment located just below the 4th Tergite containaining the genitalia

Plumose - Feathered like

Scutellum - Plate like structure between the abdomen and the thorax when viewed from above

Spiracle - (Anterior,Posterior) Breathing pores located on the side of the thorax toward the head and abdomen respectfully

Squama - where the hind margin of the wing meets the thorax there is a membranous flange known as squama

Sternites - The ventral part of the abomen of which is segmented into 4 sternites

Stigma A small cell portion arising on the outer coastal margin on tghe forewing which may not be transparent or in fact coloured

Tergites - The dorsal part of the abomen of which is segmented into 4 Tergites

Thorax - The portion between the head and Abdomen The second of 3 major components making an insect containing respiratory organs etc

 

Where do they complete their Life - Cycle?

Like other flies Hovers go through all stages of insect life: egg-larva-pupa-imago. The larvae of hoverflies are remarkably diverse for just one family of flies.

Some have adapted to aquatic life live in extremely dirty water (including stale), eating all kinds of decaying materials. In order to breathe they developed a long pipe at the rear end of the body, which they stick into the air. including the rat-tailed maggots (about 40 species).

Other larvae hunt for plant lice or aphids. Over one third of hoverflies have larvae that eat aphids (over 110 species).

Some live in decaying wood, or sap runs on live trees (33 species).

Some are a pest in agriculture eating live plant tissue such as roots, stems and flower bulbs from within or as leaf miners (about 30 species).

Like the Large Blue Butterfly, The larva of the Hoverfly, Doros profuges, is believed to live within nests of the ant Lasius fuliginosus. Little is known but one assumption is larva must either feed upon root aphids that have been herded by the ants or gain some other benefit from living within their nest.

There is much to learn and contribute about the life cycles of this interesting group with many species very poorly documented or understood.

Fig 6: The Life Cycle of The Hover Fly


What do they Eat?

Adults

Adults feed mainly on nectar and pollen, beside nectar, Hover Flies feed on honey dew produced by aphids as well. Hover Flies are one of the few kinds of insects that can digest pollen, which is protein rich development of the eggs. The surface coat of Pollen has is resistant to most insect digestive juices. The yellow patternation can reflect the amount and type of pollen the insects have eaten, they are often seen hovering or nectaring at flowers, while the larvae (maggots) eat a wide range of foods.

Larvae

In some species, the larvae are saprotrophs, eating decaying plant and animal matter in the soil or in ponds and streams. For example the rat-tailed maggot, larva of the Drone fly   Eristalis tenax is found in polluted pools and sewage. They obtain air by extending their snorkel like tail breathing tubes to reach the water surface.breaking it with feathery hairs which emerge from the tube Adults are so called because of the resemblance to Drones of bees.

Fig 7: The Larvae of the Drone Fly - Aka " the rat Tailed Maggot

.

 

Larvae may feed externally on plants or they may be internal feeders, attacking the bulbs; for example the Narcissus Fly, Merodon equestris. also known as the Great BulbFly . In other species, the larvae are insectivores and prey on aphids, thrips, and other plant-sucking insects.

Fig 8: Hover Fly Larvae Grazing on aphids

 

 

Sexing Hover Flies

Like many other flies males and females often look alike, having the same coloring, size etc. Exceptions are found especially among the drone flies, where females differ from the males. However it's always easy to tell males and females apart. Like all other flies the males have much bigger eyes. These eyes almost touch each other in the middle and are therefore closer together. Females have much smaller eyes, placed farther apart. Tiny eyes or occeli are composed of simple cells and are found at the top of the head in a triangle between the large compound eyes, perhaps this is why it is sometimes easier to get "underneath a Hover fly when it hovers. ( t he nature/ physics and of eyes in the Male also influences flight behaviour with males more able to judge distances and predate females )

A more obtrusiive method of identifying the sex of the species is to look at the underside of the abdomen, males have curbed asymetricla genitalia. The abdomen of the female is more pointed with inconspicuous genitalia.

Fig 9 Male Eye Form (Top) Female Eye Form (Bottom)

Fig 10: Viewed from above Female Eye Form (Left) Male eye Form (Right). The dotted triangle

is composed of three simple eyes or ocelli the ocellar triangle.

Hover Habitats

Hoverflies indulge in a wide range of habitats many of which are in decline. The favoured habitat for adult Doros profuges appears to be the transition zone between woodland or scrub and calcareous grassland. but clearly this hoverfly is dependent on its host the ant and factors which affect it such as the ants Northerly limit. woodland and Forest management also play crucial with much dead and rotting wood being removed.

The Golden Hoverfly Callicera spinolae is a large, colourful, hairy hoverfly that is also at risk, adults can be found feeding from Ivy flowers in autumn. It is found mainly in East Angli. The larvae live in rot holes in trees. Golden hoverflies are saproxylic, they are dependent on decaying wood.

Other species include Aspen Hoverfly, Hammerschmidtia ferruginea which lives in open aspen woodland in the Highlands of Scotland and depend on decaying oily layers in Aspen and the Pine Hover Fly, Blera fallax.

Aquatic habitats such as bog give rise to distinctive fauna. The Bog Hoverfly Eristalis cryptarum, a bee mimic also may be in decline due to the disappearance of Boggy habitat. Bog Hoverflies have been seen nectaring on marsh plants such as the flowers of bogbean, marsh marigold and cuckoo flower.

Hover Enemies

Hoverflies generally have no major "enemies aside perhaps opportunistic Spiders and Birds. Based on observations of a tame Spotted Fly Catcher, Davies (1977) notes that this mimicry does not fool it - the ability for this bird to distinguish between Bees an the less conspicuous black and yellow Syrrphinae, rubbing off stings in Bees but readily eating the hovers with no such precaution. However no species is generally without an enemy some where in the food chain.Species of solitary wasps ( Ectemnius cavifrons) specialise in taking hovers, social wasps will also take Hoverflies in summers of when numbers are high. The hoverfly parasitoid Wasp, Diplazon laetatorius, an Ichneumon Wasp, in the field, can attack, and eventually kill, over half of all aphid-eating hoverfly larvae. Failing behavioural responses the Hover Larvae may develop an immune response deterring up to 1/5 of such attacks in for example the Marmalade Fly, Episyrphus balteatus, due to host immunity. The parasitoid egg is surrounded by specialised blood cells which release poisonous compounds that kill the invader. Nevertheless many Hovers may readily fall prey to an even more insidious fate such as the insect "eating" fungal infection.

 
COMMON BRITISH HOVER FLIES

Episyrphus balteatus

Marmalade Fly

Episyrphus balteatus

(C) Colin Duke 2006

 

Heliophilus pendulas

Sun Fly

Heliophilus pendulas

(C) Colin Duke 2006

Eristalix tenax.

Eristalix pertenax.

(C) Colin Duke 2006

 Melascaeava cinctella.

Melascaeava cinctella.

(C) Colin Duke 2006

Sericomyia silentis.

Sericomyia silentis.

With Thanks (C) Leon Truscott 2007

 

Portevinia maculata

Portevinia maculata

With Thanks (C) Leon Truscott 2007

Ferdinandea cuprea.

Ferdinandea cuprea.

With Thanks (C) Leon Truscott 2007

Melastoma scalare

Melanostoma scalare.

With Thanks (C) Chris Webster 2007

Xylota sylvarum.

Xylota sylvarum.

With Thanks (C) Leon Truscott 2007

Parasyrphus punctulatus  

 

Parasyrphus punctulatus

With Thanks (C) Leon Truscott 2007

 

Epistrophe eligans.

Epistrophe eligans.

With Thanks (C) Leon Truscott 2007

 Epistrophe grossulariae.

Epistrophe grossulariae.

With Thanks (C) Leon Truscott 2007

 

 

Myothropa florea

Image (C) Colin Duke 2006

 

 

 

Epistrophe melanostoma.

With Thanks (C) Chris Webster 2007

v

Dasysyrphus albostriatus.

Dasysyrphus albostriatus.

With Thanks (C) Leon Truscott 2007

Dasysyrphus tricintum

Image Copyright (C) Colin Duke 2007 All Rights Reseved

 

 

Merodon equestris.

Merodon equestris.

 With Thanks (C) Leon Truscott 2007

 

 

 

 

Volucella pellucens.

Volucella pellucens.

With Thanks (C) Leon Truscott 2007

 Volucella bombylans.

Volucella bombylans.

With Thanks (C) Leon Truscott 2007

 

Volucella inflata.

With Thanks (C) Chris Webster 2007

 

 

Melangyna cincta.

With Thanks (C) Chris Webster 2007

 

 Melangyna lasiophthalma.

Melangyna lasiophthalma.

With Thanks (C) Leon Truscott 2007

Melangyna umbellatarum

Melangyna umbellatarum

With Thanks (C) Leon Truscott 2007

Eupeodes latifasciatus.

With Thanks (C) Chris Webster 2007

Eupeodes latifasciatus.  

Eupeodes latifasciatus.

With Thanks (C) Leon Truscott 2007

Eupeodes luniger.

Eupeodes luniger.

With Thanks (C) Leon Truscott 2007

 

Eupeodes luniger.

With Thanks (C) Chris Webster 2007

 

Anasimyia contracta.

With Thanks (C) Chris Webster 2007

 Anasimyia contracta.

Anasimyia contracta.

With Thanks (C) Leon Truscott 2007

 

Anasimyia lineata.

Anasimyia lineata.

With Thanks (C) Leon Truscott 2007

 

 Scaeva pyrastri.

Scaeva pyrastri.

With Thanks (C) Leon Truscott 2007

 Leucozona lucorum

Leucozona lucorum

With Thanks (C) Leon Truscott 2007

 

 l glauca

Leuconza glauca

(C) Colin Duke 2006

 

Chrysotoxum cautum female

With Thanks (C) David Iliff 2007

 

 

Cheilosia illustrata.

Cheilosia illustrata.

With Thanks (C) Leon Truscott 2007

 

 Brachypalpoides lentus.

Brachypalpoides lentus.

With Thanks (C) Leon Truscott 2007

Platycheirus fulviventris.

With Thanks (C) Chris Webster 2007

 

 

Sphaerophoria scripta.

Image (C) Colin Duke 2006

 

 

 

 

Rhingia campestris.

With Thanks (C) Chris Webster 2007

 

What is the definitive Reference on Hovers?

1. Stubbs, A.E. British Hoverflies An Illustrated Identification Guide 469 pages, 12 col plates, b/w illus.British Entomological and Natural History Society [ISBN: 1899935053]. 276 species are described and their identification is made easy by the extensive keys, which incorporate over 640 line drawings. The 12 colour plates by Steven Falk show 263 specimens depicting 190 different species.Good information on the family

2. Ball, S.G. & Morris, R.K.A.,. Provisional atlas of British hoverflies (Diptera, Syrphidae). Biological Records Centre, Huntingdon. [ISBN 1 870393 54 6]. 2000 Maps of distribution and analysis of flight periods are published in a BRC atlas:-

3. The Hoverfly Recording Scheme provides a good contact point for those with a shared interest in studying and recording hoverflies.

4. Gilbert,Francis - Hoverflies, Cambridge University Press, No 5 Naturalistsí Handbooks series. ISBN 0 85546 255 8

5.Rotheray, Graham Colour guide to Hoverfly Larvae by published by Derek Whiteley, Sheffield, 1993. ISBN

6. Judy Woods- -Hover flies - Insects - Section Insects

7. van Veen, M.P. Hoverflies of Northwest Europe by in English, and published in Utrecht by KNNV Publishing in 2004.

8 . UK Hoverfly Discussion Group UK Hoverflies.

9. A forum for dealing with Diptera Dipterist Forum.

10. A useful online key for Eristalis genera Eristalis key. (August 2002)

11.Gilbert (2004) Does the abundance of hoverfly (Syrphidae) mimics depend on the numbers of their hymenopteran models? ( Evolution) ISSN 0014-3820 2004, Vol. 58, No2, pp. 367 - 375 9

12. Chandler, Peter (1998) Handbooks for the Identification of British Insects: volume 12 - Checklists of Insects of the British Isles (New Series) Part 1. Diptera Royal Entomological Society

Biodiversity Action Plans

13 UK BAP Bog Hoverfly

14 UK BAP Aspen Hoverfly

15 UK BAP Golden Hoverfly

16 UK BAP Pine Hoverfly

17 UK BAP Doros Profuges

 

Acknowledgements

The author gratefully acknowledges the input of Leon Truscott, David Illif, Chris Webster, Dave Skingsley whose input would not have made this article as useful as it is and for the many folk on discussion groups who have shared knowledge, contributed and made suggestions. The work is an evolving project and the author welcomes definitive imaging for the Photo Matrix. Email Colin Duke.

The works of Stubbs Ref 1 and Gilbert Ref 5 are praised and recommended.


   Micscape Editor acknowledgement: The editor would like to thank the author and photographers for the huge amount of their time, skill and
patient photography which has been required to compile this resource. The article is mirrored with the kind permission of the author from

http://www.ukwildlife.bravehost.com/article//hovers/hover2.html

 

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