Tuesday, 13 August 2013

Identification of common garden hoverflies

Hoverflies are a colourful group of flies (Diptera) which make up the family Syrphidae. Hoverflies are given their name for their characteristic hovering behaviour, and are also referred to as flower flies as they are frequent flower visitors. Adult hoverflies feed mainly on pollen and nectar, making these insects very important pollinators.

There are 270 known species of hoverfly in Britain; these species vary greatly in size, shape and colour. Hoverflies are one of the most common insects to visit our gardens, so are very important pollinators in urban areas. If you have not already read the 30-year wildlife study by Jennifer Owen, I highly recommend you do so! Over the course of this study, Jennifer Owen recorded an amazing 94 hoverfly species in her Leicester garden – over 35% of all British species. Here are a few of the most common hoverflies you might see in your garden – have a read and see how many you can spot this summer…

Marmalade fly (Episyrphus balteatus
This is our most common garden visitor which appears in large numbers between July-August  when large numbers migrate across the Channel from the continent. Episyrphus balteatus was the most common hoverfly species found in Jennifer Owen's study, making up 15% of all hoverflies caught in her garden. It is easy to identify with its orange abdomen and unique double black bands - the only hoverfly to have such markings. 

Episyrphus balteatus on teasel - note the double black bands on the abdomen
Poppies are a popular choice!

Eristalis spp.
Hoverflies in the genus Eristalis belong to the tribe Eristalini. Syrphids in this group are easily identifiable by the strong downwards loop in a major wing vein (see below).

Wing of Eristalis sp. showing strong loop in vein
The most common species in this group is the drone fly, Eristalis tenax. This hoverfly is a good honeybee mimic (hence its common name - a male honeybee is called a drone) which can be found throughout the summer months. There are in fact 9 Eristalis species which are all quite similar - other common species include Eristalis pertinax, E. arbustorum and E. nemorum.  These hoverflies are identifiable by subtle differences in leg colour patterns, abdomen colouration, and the extent of orange triangular markings on the abdomen. Could these curious triangles be mimicking the pinched waist of the honeybee?

Eristalis sp. on Echinacea
Eristalis sp. on Coreopsis - note the orange triangular markings on the abdomen
Eristalis sp. on ox-eye daisy
Honeybee (Apis mellifera) drone: Eristalis hoverflies mimic these to deter predators

Sun fly (Helophilus pendulus)
This brightly coloured hoverfly is very distinctive with its clear yellow stripes on its thorax. The sun fly mimics the social wasp - quite effectively, some might say. Helophilus is a common flower visitor, and can also be found resting on leaves where it may emit a buzzing sound - another form of mimicry to deter predators. Look out for these lovely insects in late spring and late summer.

Helophilus pendulus on hawkbit
Helophilus pendulus basking in the sunshine

Large bulb fly (Merodon equestris)
The large bulb fly (or large Narcissus fly) is a densely hairy hoverfly which mimics bumblebees. There are four main colour morphs which mimic the colour patterns of different bumblebee species. This hoverfly got its name because its eggs are laid on the leaves of bulb plants (such as bluebells and daffodils); once they have hatched out, the larvae burrow into the bulb and stay here for up to 300 days before emerging as adults. You can spot these common garden visitors from May-September - see if you can find all four colour varieties.

Merodon equestris - this colour morph mimics the red-tailed bumblebee (Bombus lapidarius)
Merodon equestris mimicking the common carder bee (Bombus pascuorum)

Common carder bee - can you spot the difference between the model and the mimic?

Long hoverfly (Sphaerophoria scripta)
The long hoverfly is a small, yellow-and-black striped hoverfly with a slender abdomen. There are a few species within the genus Sphaerophoria but this particular hoverfly can be identified easily if you come across a male - its abdomen is significantly longer than its wings. This hoverfly peaks in numbers in July-August and is common in open grassland, gardens (including Jennifer Owen's) and urban wasteland. 

Sphaerophoria scripta on Cosmidium
The long hoverfly: note the elongated slender abdomen

Syrphus spp.
The tribe Syrphini is a very large, diverse group of hoverflies which are notoriously difficult to identify. Within this group, there are many common species in the genus Syrphus, which all possess "moustache" bands on the 3rd and 4th abdominal segments (tergites).  
 
Syrphus sp. on cornflower - note the moustache bands on the abdomen

Syrphus ribesii is very abundant in gardens, hedgerows and waste ground. Numbers peak in early June and again from July-September.

Syrphus sp. on hawkbit
Thistles provide essential forage for hoverflies

Myathropa florea
This large hoverfly is another wasp mimic with bold black and yellow markings. Myathropa florea is easily identified by the markings on its thorax: a central black patch partially bisected by a pair of pale bars. Adults of this species are fond of large umbellifer flowers, such as wild carrot, and can be seen from May-September.

Myathropa florea: note the pale hairs on the thorax
Myathropa florea are frequent visitors to wild carrot (Daucus carota)
 
Pied hoverfly (Scaeva pyrastri)
The pied hoverfly is a large hoverfly with distinctive oblique white bars on a black abdomen. This species is very fast-moving, so quite difficult to photograph (from my personal experience!). Scaeva pyrastri can be found in gardens, meadows and wasteland and its numbers peak in August, sometimes being boosted by strong immigrations. 

Scaeva pyrastri - note the oblique white bars on the abdomen


Others to look out for...

Pellucid hoverfly (Volucella pellucens): if this hovers above you, you can see right through it!
Volucella bombylans: a large bumblebee mimic with hairy (plumose) antennae
Platycheirus albimanus: a small hoverfly with beautiful silver spots

Lejogaster tarsata: a small metallic hoverfly. Males are green-bronze and females are blue
 
If you want to find out more about hoverflies, the best book out there is by Stubbs & Falk - this provides a vast amount of information on the ecology of British hoverflies as well as a fantastic step-by-step taxonomic key and beautiful colour plates to help you get started with your hoverfly ID. You can find out more about the distribution of hoverfly species by typing the latin name or geographical location into the NBN Gateway search tool.

3 comments:

  1. I like this nice and quick summary of some of the common hoverflies.

    Might have been worth mentioning the recording scheme, dipterists forum and the courses that the Field Studies Council runs.

    ReplyDelete
  2. Great site. Found some Hoverflies I had not heard of.

    ReplyDelete