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

Bath spider hybridization

Since the end of July, large spiders with long legs have been running across carpets in the house, or falling in the bath. Being agile spiders that often react to disturbance by jumping and running very fast - as opposed to crouching or playing dead - these are spiders that tend to scare people. They are males of several species of the genus Tegenaria. This guy fell in my bath a couple of nights ago and it has been the most compliant Tegenaria I've had so far. He sat still on the white bowl while I got close to its palps, but despite getting good views, I still was unable to ID it.

The two most common species in the UK are Tegenaria gigantea (=duellica) and T. saeva, and this male's palps could have been either. These closely related species differ in details of the female genitalia and of the morphology of the male palps, but their recent history is blurring the distinction between them in the north of England. Work by Peter Croucher, Geoff Oxford and colleagues from the University of York show that both spider species expanded north after the glaciations from refugia in the Iberian Peninsula. Through the vagaries of the colonisation process until recently, they had a mainly segregated distribution in the UK, with T. gigantea in the east of the country and T. saeva in the west.

Distribution in England and Wales of Tegenaria saeva and T. gigantea based on 10x10 km grid squares of standard maps (Ordnance Survey, the national mapping agency of Great Britain). Black squares, T. saeva; white squares, T. gigantea; grey squares, those containing both species. Spiders with intermediate morphologies are not included (figure from Croucher et al 2007).

In the south of the country, both species distributions meet in a narrow stable zone, in Dorset, where hybridisation appears not to be very common and when it happens results in high hybrid mortality. Since the 1970s, however, both species have expanded into Yorkshire and in this region they often occur in the same places and hybridise commonly, so that their species boundaries are falling apart and many morphologically intermediate forms are found. As Hull is in an area of high hybridisation, my inability to ID the spider might have more to do with my limitations, but there is a high chance there is no "pure" T. gigantea and T. saeva in this area any more, and that these house spiders are actually merging into one as they carry on colonising towards the north.

More information
Croucher, P., Oxford, G., & Searle, J. (2004). Mitochondrial differentiation, introgression and phylogeny of species in the Tegenaria atrica group (Araneae: Agelenidae) Biological Journal of the Linnean Society, 81 (1), 79-89 DOI: 10.1111/j.1095-8312.2004.00280.x
Croucher, P., Jones, R., Searle, J., & Oxford, G. (2007). CONTRASTING PATTERNS OF HYBRIDIZATION IN LARGE HOUSE SPIDERS (TEGENARIA ATRICA GROUP, AGELENIDAE) Evolution, 61 (7), 1622-1640 DOI: 10.1111/j.1558-5646.2007.00146.x

German wasp hunting a garden spider

Garden spiders have been quite obvious in the garden for a few weeks now, sitting in the middle of their webs waiting for flying insects to get entangled in their sticky threads. Garden spiders are preyed upon by other animals, including wasps - which later in the year, when garden spiders are larger and more powerful, will eat them in return. This German Wasp (Vespula germanica) caught a middle size garden spider, I saw it fly with it and settle on a drain pipe to subdue it. If the wasp stung the spider I do not know, but its abdomen was curled underneath. After giving the spider a good chew and positioning it under its legs, the wasp flew away. Wasps hunt -and scavenge, famously at picnics -  to feed their larvae.

The wasp with its prey just before flying away

A large garden spider with a wasp prey in October 2008

UPDATE 24/08/11: corrected the title, which said common wasp.

Courting spiders

I have posted on this common garden species, Linyphia triangularis courtship before, but I had the chance of observing this pair of spiders courting in the garden yesterday and take some photos. The male is larger, reddish, with an elongated abdomen and very large chelicerae. The female, at the back, has a rounded abdomen with a black and white pattern. As you can see in the bottom photo, there is a recent moult hanging from the web - I presume is the female's, as I cannot see the large chelicers of the male. In this species, the male does a form of mate guarding, sharing the female's web to wait until she has moulted and therefore she is ready for mating, and fending other approaching males off. The male vibrated its pedipalps and abdomen and slowly approached the female.

Lesser Marsh Grasshoppers

Our back garden opens to an access road, on it there is an area of south facing rough ground which used to be concreted over. With time, grass has taken hold and now it is a little wild area. I cut the grass once a year trying to promote a meadow, and have sown wildflower seeds and naturalised Birds Foot trefoil, oxeye daisies and foxgloves. Today we had a big surprise when in a matter of minutes we came across two species of grasshoppers there, the first time we come across grasshoppers there. We came across at least two female Lesser Marsh Grasshopper, Chorthippus albomarginatus, a green one and a brown one, and a calling male Field Grasshopper, Chorthippus brunneus. Both are common species in the U.K. and are present in the nearby wildlife garden. I anticipate interesting grasshopper behaviour watching! watch this space for more grasshopper posts.

Lambs ears shieldbugs

Although I keep Lambs ears (Stachys byzantina) in the garden for the benefit of the Wool Carder bees this plant also attracts many other bugs. They provide a lot of structure with their large woolly leaves, and spiders, harvestmen and ladybirds are often found on them. They also offer sheltered overwintering opportunities. My other favourite lambs ears bug is a true bug, the pretty shieldbug Eysarcoris venustissimus, also known as the Woundwort shieldbug, as their usual feeding plant is the native Hedge Woundwort (Stachys sylvatica). This is a small shiny bug that appears in a single generation per year. The adults are bronze, grey and white with fine black speckling. They emerge from hibernation in April and can be found mating on May. Females lay their eggs in Stachys plants. Nymphs can be easily found on July and August and by September there is a new adult generation. Today, I watched at least nine nymphs in various stages of development on the Stachys plant. Nymphs are green and black or pinkish and black. All the nymph photos were taken today. 

An early instar nymph. The object near it are seeds of Circaea luthethiana

A group of Wounwort shieldbugs with a green shieldbug nymph.

A last instar nymph. They can be recognised by their black wing buds

A mating pair on Stachys bizantina (11/5/11)

UPDATE 25/08/11. Replaced a photo with the early instar one.