Summer Hoverfly identification

Late summer brings out masses of hoverflies in the garden. They buzz around the fennel and the wild rocket and the red valerian. Despite their superficial similarity - many are stripy yellow and black - there are 276 British hoverfly species (family Syrphidae). With a little attention to detail, though, and armed with a good identification guide (I use British Hoverflies, by Alan Stubbs and Steven Falk) it is relatively easy to identify them, although there are several species complexes hard to ID to species level. The following nine species are amongst the most common in gardens in July and August. On the top photo, the, by far commonest, Episyrphus balteatus, the marmalade fly, hovering. This is a very distinctive species, due to its double abdominal dark bands. Individuals can occur in large aggregations, and are found in groups on dandelion flowers.

Sphaerophoria sp. a male on Erysimum

Female Sphaerophoria sp. on fennel.

 Scaeva pyrastri, female hovering and Red Valerian

another Scaeva pyrastri on wild rocket

Syrphus on Large Bindweed. This is another very common species.

Female syrphus on Erysimum

Platycheirus scutatus on Japanese Anemone

Myathropa florea sunbathing.

The tiny Syritta pipiens, with distinctive swollen back femurs, on Nipplewort

Eupeodes luniger hovering on Herb Robert

The dronefly Eristalis tenax feeding on Lavender

An impressive slug

A showery day, I come across this enormous Arion slug crossing the garden path. It must be close to 15 cm. Identification to species level is difficult to impossible as they are distinguishable by examination of internal genitalia characters - or molecular genetic analysis, and hybrids are common. British large Arion slugs are made of several species complexes, Arion ater/rufus A. lusitanicus and A. flagellus. Both groups are very polymorphic slugs, from almost white to black, including all shades of brown yellow red and orange. I have never found the the black morph in the garden, but a good representation of the others abound. The polymorphism of these slugs in the U.K., not only in colour, but also in genital characters, might stem from common hybridisation between several subspecies that colonised the British Isles from Europe, postglacially but also in more recent human introductions. Distribution changes might also come about due to expansions as a result of climate change. In addition, the slugs - except for A. flagellus - are able to self-fertilise and form relatively homogeneous populations, which might give the impression of being a separate species.

 Arion slugs had deep tubercles on their backs, and no keel. At the end tip is the mucus gland, producing an extremely sticky mucus. Unlike the yellow slug, which is strictly nocturnal, Arion slugs are active all around the day, provided that it is damp. When disturbed they show a characteristic behaviour: they contract their bodies into an almost round shape and retract their tentacles inside their mantle. Inspired by a post in Myrmecos, I set the photo vertically. I had to use a white plate - instead of bowl - and allow the slug to relax and start to crawl out. 

A very yellow specimen

A disturbed Arion

A selection of colours found in the garden

The black morph of Arion sp.

References

Noble, L. R. Jones, C. S. (1996). A molecular and ecological investigation of the large arionid slugs of North-West Europe: the potential for new pests The ecology of agricultural pests: biochemical approaches Ed. William O. C. Symondson, Systematics Association, special volume. Clarendon Press., 53, 93-132
Evans, N. (1986). An investigation of the status of the terrestrial slugs Arion ater ater (L.) and Arion ater rufus (L.) (Mollusca, Gastropoda, Pulmonata) in Britain Zoologica Scripta, 15 (4), 313-322 DOI: 10.1111/j.1463-6409.1986.tb00232.x
UPDATE 30/08/11: reference added and Arion ater in a photo caption changed to Arion sp.

A new adult generation of Woundwort shieldbugs

Every day I check the Lambs ears for the Woundwort (or Bronze) shieldbugs, Eysarcoris venustissimus. They are usually immobile and once you've found them once, they are easy to find, although they will hide under the leaves if they feel threatened. They form clusters on the tips of leaves, not only of the Lambs ears, but also on the Enchanter's nightshade, which covers the ground on this side of the garden. Today I spotted the first adults of the year, four of them, one on a cluster of final instar nymphs; another, still white (above), looked like it had just moulted into adulthood.

A new and shiny adult Woundwort shieldbug adult on Lamb's ears

A fresh adult with three final instar nymphs

These are some nymphs on the seed stalks of Hedge Woundwort: their colours make them almost invisible at a distance, as the stalks also have a contrasting green/black pattern.

Swift hoverfly settled down for the night

This hoverfly species, Scaeva pyrastri, is a challenging photographic subject. I find it particularly flighty, and many a time I have chased it across the garden as it fed on Verbena bonairensis, Buddleia, Hebe or Red Valerian. It is very aware of shapes approaching, and it cunningly and swiftly flies out of range. You really have to stalk it for close ups. S. pyrastri is a migrant hoverfly which flies from the continent to rear a generation in northern Europe and all my records are of July and August, of single individuals. Their numbers vary greatly from year to year. It is a large, handsome hoverfly, males giving the impression of having a disproportionately larze head (as above) due to their enormous eyes, which are distinctively hairy, and like in other hoverflies meet on top of their heads. The species has very characteristic white markings in the black abdomen. Adults are found in a range of flowers, while the larvae feeds on ground aphids. This male had chosen to settle in the startlingly red rowan berries and it allowed me to approach to the minimum focusing distance of my camera.

Loving the fruit

Our apple and plum trees fruit in August, and there are many bugs that love them, some quite surprisingly. Slugs, springtails, woodlice and fruit flies gorge on fallen apples, and comma and speckled wood butterflies feed on blackberries, but recently I noticed a few new characters in our produce. Seven spot ladybirds clustered on overripe plums (we were away and failed to collect them) and honeybees and wasps joined them. The common wasp (Vespula vulgaris) above, kept coming back to feed on a damaged spot on this fallen apple. Sweet, sweet fruit!

7 spot ladybirds and a wasp

honeybee in plum