Small, spiny and very very hungry

It must be the time of year, but after writing about a Platycheirus hoverfly larva, I found another one - a different genus, but the overall form and fused posterior respiratory processes (PRPs) make it clearly a hoverfly (Syrphidae); larvae of some other fly families such as the Pipunculidae have PRPs that appear fused, but a close look reveals they are not.

Dorsal view of the hoverfly larva - about 10mm long and the head end is bottom left.

This is quite different to the smooth, 'maggoty' Platycheirus larva with its yellow-green lines of fat. Here, small bumps and spines can be seen on the top and sides plus lots of little black speckles (see below). The PRPs are a pale brown colour and the dark line down the middle is the long thin 'heart' which could be clearly seen pumping while I took this shot. Referring as ever to Rotheray (1993), the features soon brough me to two possible genera, either Scaeva or Eupeodes (previously known at Metasyrphus). Let's look a little more closely...

PRPs and posterior clasper of Eupeodes luniger

Close-up of PRPs and posterior clasper of E. luniger. The green polygon outlines the clasper and the red lines follow the directions of the lower pair of spiracles, showing that they diverge strongly.

The photo legends give the game away - it's Eupeodes luniger - but let's consider why. Firstly, the top photo of the PRPs (themselves within a roughtly triangular surround) shows that the black patches are made of tiny dark spines or 'spicules' - something that separates Eupeodes from Scaeva. Most Eupeodes are found on conifers, but two are commonly associated with ground layer vegetation - E. corollae and E. luniger. The larvae of these (as with Platycheirus they are aphid predators) are fairly similar, but can be separated by looking carefully at the spiracles - the slit-like openings of the PRPs. In corollae the lower pair are almost parallel, but in luniger, as here in the lower photo, they diverge strongly. The clasper is also typical of Eupeodes and, as shown clearly in Rotheray (2003), is used to grip the edges of leaves or thin stems (here it is gripping a thin wooden spatula being used to position it under the microscope). This is a surprisingly unusual adaptation in hoverfly larvae many of which do sometimes fall off leaves as they can not easily grip them and have to rely on the surface tension created by moisture on leaves; some exude saliva just ahead of themselves and use this to grip (Rotheray & Gilbert 2011). The locomotory structures of Eupeodes are also known to be complex (besides the presence of a clasper) and the photo below hopefully gives some indication of the folding and creasing that forms the prolegs and associated structures on the underside of the larva. Though migratory, both E. luniger and corollae are common in a range of habitats in Britain, and their similarity to Scaeva remains when adult. This specimen, as before, has now been released into our garden to feed on aphids. More soon!

The complex prolegs and locomotory growths on the underside of Eupeodes

References

Rotheray, G.E. (1993). Colour guide to hoverfly larvae (Diptera, Syrphidae). Dipterists Digest 9: 1-156.
Rotheray, G.E. (2003). Aphid Predators. Richmond, Slough.
Rotheray, G.E. & Gilbert, F. (2011). The Natural History of Hoverflies. Forrest Text, Tresaith.

Miniscule mummification

Following yesterday's post about aphid-feeding hoverfly larvae, I went out into the garden and found evidence of another aphid-bothering insect - the empty skin or 'mummy' of an aphid stuck to the underside of a sycamore leaf by a domed silken cocoon on which it lies. The whole arrangement is only about 2mm long so it was tricky to get good photos even under the microscope due to the white structures tending to overexpose, but this is what I managed...

Aphid 'mummy' attached to a silken cocoon

There are numerous parasites of aphids (technically 'parasitoids' as they develop inside them) and one key group is the aphidiiine wasps (subfamily Aphidiinae within the Braconidae), tiny wasps that lay eggs directly into living aphids. Some, such as the genus Aphidius, produce larvae that cut their way out of the abdomen leaving an empty aphid with a neat lid. However this arrangement - an aphid 'mummy' atop a domed silken cocoon containing pupa/e (the larvae will have fed on the aphid internally) - is typical of the genus Praon.

Aphid mummy attached to the top of a Praon cocoon - the developing Praon have left the aphid and have pupated beneath it.

When a Praon adult leaves the cocoon it cuts a small hole through which to exit, but the photo above shows the cocoon to be intact and skirt-like with the developing wasp/s inside. It is impossible to identify further at this stage, although P. volucre is a common species - however, I have retained the leaf and cocoon and hope to raise at least one adult for identification - I'll be looking out for a tiny black wasp with orange-yellow legs: another often-overlooked gardeners' friend!

Great hovering maggots

When collecting brambles to feed our stick-insects, small invertebrates on them often end up indoors as stowaways. As the bramble leaves are destined to be rapidly eaten, I tend to put the invertebrates back outside - recently I've unexpectedly found moths, aphids, a parasitic bee, small spiders, barklice and others. Some of these get out of the stick-insects' containers and wander about the place. So, I wasn't too surprised this morning when I saw something wiggling its way across the lid. The pointed head end with a dark point and pulsing legless 'maggoty' movement made it clear this was a fly larva - in particular a hoverfly (Syrphidae).

Hoverfly larva, the head end is at the bottom of the photo

Being a bug-nerd, before putting it back outdoors, I decided to take a closer look to see if I could identify it. Using the standard work by Rotheray (1993), it is clearly not Microdon (which is domed in shape and has a band of bristles aruond the edge of the body), but does have a colour pattern. It's not green (though the fat deposits are a yellow-green colour), nor does it have dorsal projections, although there is some dorsal striping. The next step is to look at the 'posterior respiratory projections' (PRPs) at the rear end.

Rear end of the hoverfly larva showing PRPs with pale bases and about as wide as long.

The larva is somewhat flat and so 'subrectangular' rather than square-ish in cross-section, and has dorsal stripes merged smoothly at the head end - these features indicate that it is in the genus Platycheirus.

Head end of Platycheirus larva showing the point where dorsal stripes meet smoothly

Platycheirus larvae are associated broadly with low or ground-layer vegetation and feed on aphids - definitely popular with knowledgeable gardeners! However, the ecological and biological details of Platycheirus larvae, including differences in feeding strategies between species, are poorly understood. This does not have clear chevrons of fat so is probably in the fulviventris group, although not P. fulviventris itself as this is associated with wetland monocots rather than hedgerow brambles. Consulting Stubbs & Falk (2002), fulviventris is in the clypeatus group and it may well be the common and widespread P. clypeatus although the only way to be certain would be to raise it to adulthood and the habitat is more suited to another common species P. albimanus although this falls outside the fulviventris and clypeatus groups. Fortunately for the larva, it is back outside on aphid-laden bramble in our garden.

Dorsal view of the Platycheirus larva showing the dark gut between patches of fat

References

Rotheray, G.E. (1993). Colour guide to hoverfly larvae (Diptera, Syrphidae). Dipterists Digest 9: 1-156.
Stubbs, A.E. & Falk, S.J. (2002). British Hoverflies. BENHS, Reading.

A tale of two pincers

In case you haven't heard of iSpot, it is a UK-based online species identification site, linked to the Open University and Opal (the Open-air Laboratory), where anyone from beginner to expert can post photos of wildlife either with or without an identification, for others to agree with or amend as appropriate. Some groups are relatively straightforward to identify from photos (many birds and butterflies for example) whereas others are more difficult (or need detailed close-ups of key features) such as lichens, ichneumons and many flies. So, when a set of close-ups of a pseudoscorpion appeared on iSpot with a suggested identification of the rare species Kewochthonius halberti, my interest was piqued and I decided to investigate...

The specimen had been found inland whereas K. halberti is considered coastal, associated with the high-water line. However, like many pseudoscorpions (they form an order of arachnids), their small size (up to 4mm) and secretive habits, being found under stones, logs, debris etc., this species is poorly understood and it is always possible that it is associated with other habitats as well. So, I consulted the key in Legg & Jones (1988), the standard work on British species (which is very good value from here by the way), bearing in mind that even such a well-respected text may have omissions given the poor level of knowledge regarding the group covered.

The pseudoscorpion in question, preserved in ethanol

Having worked through the key, I too came to K. halberti, but it didn't look right - the shape of the cephalothorax (the front segment with a plate covering the head and thorax) narrowed towards the front for example, and so I posted a comment on the observation on iSpot and began a discussion with the original observer, Kris Hart (who kindly gave permission for me to use his photos here).

The movable finger of the pedipalp pincer showing small blunt teeth along the edge.

Some features were clear such as the tergites (plates running across the top of the abdomen) having no longitudinal split down the middle. However, whether or not the chelicerae (the jaws attached to the front of the head forming small pincers rather than the large scorpion-like pincers on the pedipalps) were more or less than 2/3 the length of the cephalothorax was a less clear decision. I measured them as 0.7 of this length but given the margin for error, this was a borderline result. The teeth on the edge of the pedipalp finger (above) match those of K. halberti, but this species is only 1.2mm long, whereas the specimen is twice this length - definitely outside the plausible range of variation.

So, I returned to the key and chose the 'smaller chelicerae' branch which took me to the genus Neobisium. This immediately looked promising as the species were of the same size as the specimen, and also showed more or less the same shape of cephalothorax. Indeed, keying it out soon led to the 'common neobisid' N. carcinoides - probably Britiain's commonest pseudoscorpion. The final feature indicating this was the shape of the galea - the small bump on the outside edge near the tip of the 'finger' of the chelicera.

The movable finger of the chelicera of N. carcinoides. The galea is the small round bump near the tip to the bottom left of the photo and is a low, rounded structure rather than being more highly raised.

So, a possible rare species turned out to be a very common one. This often happens and may seem disappointing, but not so - apart from being a more accurate record, it illustrates the process of using fine structural or morphological details to aid identification. It also provided an opportunity to look at a specimen from a group that isn't seen very often (without finely sieving leaf litter or other suitable debris) and become more familiar with it. Variaous possibilities were considered - was it an adult? (juvenile pseudoscorpions are very poorly understood); had the preserving fluid had an effect on colour? It also showed how a resource such as iSpot can be used to collaborate in the identification of difficult specimens as I asked Kris for extra photos, further details and so on through the comments facility. Lastly, it has highlighted an area of difficulty in the key - something that can only be done by using it. So, yes it's a common species, but also very much a worthwhile piece of work. Thanks Kris!


Reference

Legg, G. & Jones, R.E. (1988). Pseudoscorpions. Synopses of the British Fauna (New Series) 40: i-vi, 1-159.

The Bluebells and the Town-hall Clock

In most of Britain, bluebells (Hyacanthoides non-scripta) are a familiar sight in the spring - a few here and there in hedgerows, grassland and on western sea cliffs, but if you visit ancient woodlands, you have a good chance of seeing carpets of these flowers...

Bluebell Wood in the Holywell Estate in Hampshire

Bluebell flowers are all on one side of the stem forming a 'raceme' of drooping flowers, each a cylindrical bell shape with two blue bracts at the base, the petals (more technically 'perianth segments' as they are fused) curled back strongly at the tips, and the anthers cream-coloured. However, you might see some that aren't quite like this - either the introduced Spanish Bluebell (H.hispanica) or, more commonly, the hybrid between the two, H. x massartiana, both being garden escapes.

H. hispanica looks superficially similar to the native bluebell, but the flowers are not all on the same side of the stem, and are not all drooping, the tips are flared outwards but not tightly curled back, and the anthers are blue. The hybrid is sometimes confused with this species, but has features intermediate between the two such as flowers that curl slightly back at the tips.

If you do visit an ancient bluebell wood, however, don't forget to look around for other species - bluebell carpets are an impressive wildlife spectacle, but this type of habitat supports many other species, some of which may be less familiar, such as Moschatel (Adoxa moschatellina), also known as 'Town-hall Clock'.

The pale green  trifoliate leaves of Moschatel

The tiny pale greenish flowers of Moschatel

Moschatel, named after its musky smell, is common in some places, particularly ancient woodlands on damp, fertile soils (and sometimes mountain ledges - in southern Europe, it is a mountain species), but is often overlooked. The trifoliate (three-part, like clovers) leaves are fairly easy to spot, each of the three leaflets further split into three lobes, but the tiny flowers can be elusive. There are five flowers at the end of each long stalk and these are arranged as a cube; four facing sideways at right-angles to each other, the fifth pointing straight up. This gives the plant its alternative 'town-hall clock' name as it recalls the shape of old clock towers with four faces and a roof on top. However, if you want to see it, you have to be quick - it soon dies back and for much of the year there is little evidence of it above ground.


There are many other ancient woodland indicators that can be found by visiting the right sites in spring - as I write, some are still visible, but soon the summer species will take over for another year...

A bluebell wood from ground level

Making the summer

You may have heard the old adage, 'one swallow doesn't make a summer', but what about 300 or more? Given the exceptionally wet weather recently (following a dry winter and an unusually hot early spring leading to drought), the feeling that summer might be coming is certainly a pleasant one, even though objectively the rain is welcome in farms and gardens. So, while spending the weekend at Downton for the Cuckoo Fair, although I'd been seeing small numbers for a few weeks, it was good to see a more sizeable flock of swallows (Hirundo rustica) that had just arrived...

There were about 300 in total and as you can see, when this video was taken (at about 11:00) they were mostly feeding low over the River Avon with some skimming low over the fields - traditional grazed pastures favoured by swallows. By the afternoon and evening, their feeding behaviour had changed - they were flying higher and were not following the river; instead they were moving more widely over the fields, occasionally shifting en masse as a loose flock, presumably following the patterns of movement of their insect prey.

Filming these birds with their rapid, darting flight isn't too difficult (as long as it's just a broad view that you want), but photography is another matter - group shots aren't too tricky, but focusing on individuals is another matter, hence the blurriness, though it is possible to pick out the blue head and the white flashes on the underside of the tail.

Swallows feeding over the River Avon, Downton, Wiltshire

Swallows performing close aerial passes...

Within this flock of swallows, there were a few other birds that looked different - one (black rather than blue, with a white rump-patch) was the house martin (Delichon urbicum) several of which could be found away from the main swallow flock in a nearby field. Another was smaller, fairly uniform on top, with a pale underside and dark throat-collar - the sand martin (Riparia riparia) which is also associated with this low-over-water feeding behaviour.

Among the chaos of the swallow flock, one of the three sand martins seen - and the best photo I could manage!

As well as heralding summer in the UK, migratory species such as these can be excelllent (if sometimes worrying) indicators of environmental conditions. Wintering in southern Africa, Britain's swallows face a long and hazardous journey, with perils including starvation, exhaustion and death in storms. The precise routes have not always been clear, but tracking technology has provided useful data and we now know that some cross the Sahara while others follow the west coast or fly up the Nile Valley. Rather than gaining much weight prior to migration, swallows find food en route (they fly by day and at low altitude), progressing around 200 miles (320km) each day.

It's long been known that annual weather fluctuations affect swallow populations - a cold, wet breeding season reduces insect numbers and hence chicks starve - but there are longer-term trends with populations having fallen across Europe since around 1970. Although the precise causes are uncertain, there are a number of likely reasons for this:

• The effects of climate change on swallows' African wintering grounds and migration routes. Certainly,  swallows are returning to their breeding grounds in poorer condition and laying fewer eggs than was previously the case. One factor seems likely to be the expansion of the Sahara desert,  making this already major barrier increasingly difficult to cross.
• The effects of climate change in Europe. Cold springs (including late frosts) reduce insect numbers. Similarly, very hot, dry summers cause pools to dry out, also reducing insect numbers, and as well as the risk of starvation, chicks die from heat exhaustion and dehydration.
• Land use changes across Europe may be reducing the numbers of nest sites and flying insects. Swallows tend to forage over grazed pastures (as seen at Downton), and the loss of cattle grazing has impacted on swallows in some areas.

So, there are clear concerns about swallow populations (as there are about many other migratory species) and solid evidence for population declines even if some of the causes are not fully understood. It is also a good example of the difference between 'weather' and 'climate' - in very simple terms, climate can be seen as 'average weather'. However, if you have outbuildings (garage, barn, workshop etc), there are some things you can do to encourage swallows to nest - they like to nest on dark ledges and in nooks and crannies, as these stay warm in cold weather and cool in hot weather. They can enter buildings via surprisinly small holes and need very little light (dark areas are at less risk from predators) - my favourite swallow nesting site is at Monkey World Ape Rescue Centre in Dorset where swallows nest high up inside one of the Chimpanzee viewing galleries, darting between visitors as they fly to and from the nest. To encourage swallows to nest in an outbuilding, the following should help:

• Make a small opening (minimum 50 mm high & 70 mm wide), under the eaves or simply leave a window or door open if security is not an issue
• Attach a nest platform where you would like them to be - high up, out of the reach of cats. Use flat pieces of wood to make an open-fronted box (the front should be tilted slightly upwards or have a low lip to stop the nest falling out - robin nest-box designs are sometimes used), or if you are feeling more creative, attach a sawdust-and-cement or papier-mache cup to a wooden backing plate. Block off places where you don't want the birds to nest.
• Put a plastic bag below the nest to catch droppings 
• If the weather is very hot, put an old carpet or blanket on the outside of the roof above the nest and soak it regularly with water. A couple of buckets of bathwater on such material takes several hours to dry and helps keep the temperature down inside the outbuilding.

Now, I think I've spotted a suitable nesting spot, so I'm off to rummage through my timber store to make a box. If it works, watch this space for nest photos! Until then...

Even swallows have to rest sometimes..

Focusing on the familiar IV: ladybirds Part 3

After a short holiday (hence the gap between posts), I'm back and thought I would celebrate the sunshine with another in my occasional series about more familiar species. I've looked at several species of ladybird already, but there are others that you are likely to encounter and today I want to move on from the red-and-black species to look at the Orange Ladybird (Halyzia 16-guttata or more correctly sedecimguttata).

Orange Ladybird, Halyzia sedecimguttata

This is an attractive species, 4.5 - 6mm long with 12-16 (usually 16) pale spots on an orange background. The elytra (wing cases) have a translucent edge - you can see the legs through it - as does the pronotum which leaves the eyes visible from above. It's usually a woodland species, but is becoming more common on trees and shrubs in urban areas, especially where there is ivy - this one was brought indoors by accident on bramble destined to be stick-insect food and was collected from beneath scots pine and ivy. Sycamore and ash are generally considered the main hosts, but hawthorn is now also used widely by adults and larvae, with records also coming from dogwood, lime, hazel, sallow, birch, field maple and occasionally conifers. It feeds on mildew rather than the plants themselves, and hibernates in leaf litter or sheltered parts of trees. Being mildew-feeders, they breed in June & July, later than other (i.e. aphid-feeding) ladybirds as they have to wait for sufficient mildew to develop in order to feed their larvae. Though more common in the south, they can be found throughout the UK, as far north as the Orkneys.

Further reading

Majerus, M. & Kearns, P. (1989). Ladybirds. Richmond, Slough. An excellent little book with detailed keys to species, including the 'micros' - a new edition is being prepared.

Majerus, M., Roy, H., Brown, P. & Ware, R. (2006). Guide to Ladybirds of the British Isles. FSC, Preston Montford. A fold-out laminated sheet perfect for beginners.

Roy, H., Brown, P., Frost, R. & Poland, R. (2011). Ladybirds (Coccinellidae) of Britain and Ireland. FSC, Shrewsbury. Details of all species including maps, identification features, ecology and so on.