What's in the box? No.4 - some very small bits of very small beetles...

In case you've not read any of my 'what's in the box?' posts before, it is an occasional series detailing the specimens (generally leaf beetles, family Chrysomelidae) that land on my doormat when other entomologists send me specimens as part of my role as coordinator of the UK Leaf & Seed Beetle Recording Scheme.

Sometimes these are quite mysterious and have included both an aberrant specimen of a common species and a species new to the country (most exciting to a bug-nerd!). Next mission - a species new to science... but until then here's a close look at the contents of a small tube of tiny beetles that arrived preserved in ethyl acetate. In this case, the identity was clear as a letter was included stating that these were voucher specimens of Aphthona pallida from North Yorkshire in northern England, a small (1.5-1.8mm) species of 'flea beetle' found on Geranium and Erodium, in this case Geranium pratense.

Dorsal view of A. pallida showing the brownish-yellowish elytra and pronotum, and black head. Note the relatively coarse punctures on the elytra and the microsculpturation that is just visible between them (clearest around the centre of the image). The area covered in this photo is about 1.2mm wide

Ventral view of A. pallida showing sculpturing and bristles on the legs and abdomen; note the large hind femurs.

This may be nothing special in itself, but until 2009 there was considerable confusion between this species and A. nigriceps in Britain, with various taxonomic authors treating them as separate species, the same species, or subspecies. Not easy for those trying to produce accurate species records. They have been treated as separate species in some key continental European texts such as Warchałowski (2003) which separates them using the presence of a dark sutural stripe in A. nigriceps. Then, in a 2009 paper, Sinclair & Hutchins discussed the status of A. pallida, concluding that it was definitely a British species and separating it from A. nigriceps most clearly by the shape of the tip of the aedeagus.

Further work (summarised in the accompanying letter mentioned above which was from Jim Jobe, Coleoptera recorder for the Harrogate and District Naturalists' Society) suggests that the darkened suture is an unreliable feature and that the aedeagus is the only certain way to separate these two species. I do not have a specimen of A. nigriceps to hand, but there is an excellent image here, including the aedeagus. Comparing this with the aedeagus of A. pallida below, it is clear that the aedeagal tip of A. nigriceps is flatter/broader, a feature noted by Sinclair & Hutchins (2009).

Aedeagus of A. pallida; note the tip which is less flattened/broadened than that of A. nigriceps.

So, what is the upshot of this? Well, firstly A. pallida is a clear addition to the British list and can be separated from A. nigriceps using the aedeagus - a somewhat fiddly dissection, but it provides a reliable feature. Secondly, it does appear that the relevant part of the generally excellent (though expensive) Warchałowski (2003) is incorrect i.e. couplet 25 on p.396 as this uses the sutural feature as a separator. Lastly, it is likely that many British specimens labelled 'A. nigriceps' are actually A. pallida and ongoing work on this is due to be published in the relevant literature; when this occurs I shall post an update here. It will also allow me to amend this part of my test key to the Chrysomelidae when I start producing the final version this winter.

References

Sinclair, M. & Hutchins, D. (2009). Aphthona pallida (Bach, 1856) (Chrysomelidae) is a British species. The Coleopterist 18(3): 155-157.

Warchałowski, A. (2003). The Leaf-beetles (Chrysomelidae) of Europe and the Mediterranean Area. Natura Optima Dux Foundation, Warsaw.

Some are squat and some are squatters: more of the intertidal

About a year ago when my blog was just getting going, I posted photos of some specimens from a Southampton Natural History Society (SNHS) visit to Calshot Beach in southern England, a site with areas of stones, gravels, sands and shingle as well as nearby saltmarsh (the latter not covered here). That visit produced some excellent views of spectacular species such as the Dahlia Anemone Urticina felina, and we were keen to see what could be found this year. This is an annual SNHS event and the findings go towards building up a late summer/early autumn species list for the site - this year, although we picked low tide, it wasn't as low as last year's so we expected a somewhat different range of species.

Some species, or their signs, were familar from last year, such as the shells of Haminoea sea slugs, the Snakelocks Anemone Anemonia viridis, and the introduced North American bivalve, the Quahog Mercenaria mercenaria. Many others were different however - some are presented here and I hope you enjoy them. The first group I want to cover are the molluscs, starting with some primitive armoured species (the chitons) and then a larger (and edible) introduction.

Lepidochitona cinerea (family Ischnochitonidae). Probably the commonest North European chiton, this species is often found on the underside of stones, though this one was on a large bivalve shell. Though it looks smooth, the valves (sections) are rough to the touch, like fine sandpaper. This specimen is about 15mm long - the maximum is about 24mm.

The fairly common Acanthochitona crinitus (family Acanthochitonidae). The valves are less smoothly arranged than in L. cinerea and there are 18 tufts of coarse bristles. This specimen is about 20mm long - the maximum is about 34mm.

Chitons (class Polyplacophora) have a mantle skirt which forms a toughened 'girdle' around the whole edge of the animal and this is where the fringing spines etc are found. The head is small and covered by the girdle and the dorsal surface generally has armoured 'valve plates' as seen here. They graze plant and algal material from hard substrates and, like limpets, are able to withstand wave shocks without being dislodged.

The introduced Mediterranean/Biscay species Crassostrea gigas, the Portuguese Oyster. The shell has several large wrinkles and smaller concentric lines. It can grow to 180mm in length and is attached to the substrate at the hinge end - here it is attached to a dislodged stone.

Sticking with shelled species, but adding legs, a number of crustaceans were also found. As well as the common shore crab Carcinus maenas, some possibly less familiar species were worthy of a photo or two...

OK, this probably is quite familiar - it's the common hermit crab Pagurus bernhardus, using the shell of a Netted Dog-whelk Hinia reticulata. Gotta love hermit crabs! Note the larger right claw which is covered in small knobs or 'tubercles'.

One of my favourites, the Hairy Crab Pilumnus hirtellus. It is covered in hairs which are broader at the tip than the base and help camouflage it among the sediment and detritus of the intertidal zone. The shell is up to 20mm across, which is about the size of this specimen, doing its best to hide in a white tray with a few scraps of seaweed.

Another favourite, and less commonly seen, the squat lobster Galathea squamifera. The rostrum is triangular and pointed with 4 spines on each side, the rear ones also being the smallest. These spines are usually red-tipped (as here) as are those on the outer edge of the claws. The claws are also covered in flat scale-like tubercles. Despite the claws, it filter-feeds on suspended detritus.

The shrimp Palaemon elegans with a straight (rather than clearly up-curved) rostrum and dainty little claws. Note the telson (the flap at the end of the tail) doesn't have any lateral spines. These features separate it from similar species such as P. serratus.

Lastly, I'd like to introduce a couple of soft-bodied species - not the large showy ones, but a couple that are often likely to be overlooked.

The sea anemone Sagartia troglodytes. Similar to S. ornata (some specimens may be extremely difficult to separate to species), but this one clearly shows the pale brown column darkening at the top with speckles. Note the numerous tentacles; there may be up to 200 arranged in a roughly hexagonal pattern (here it is clear that the arrangement is not circular). The attachment to a buried stone is typical.

The Leathery Sea-squirt Styela clava. This is an introduced Pacific species and can be found attached to stones (as here) and pilings around the south-west coasts of Britain.

As with last years post, this is only a snapshot of what can be found on a diverse section of intertidal habitat, but hopefully an interesting one. However, it does illustrate how important volunteers are for recording wildlife, especially less 'popular' groups like many in marine and intertidal habitats - and with knowledge comes at least the potential for conservation.


References

Crothers, J. & Crothers, M. (1988). A key to the crabs and crab-like animals of British inshore waters. Field Studies 5(5): 753-802 (revised reprint).
Gibson, R., Hextall, B. & Rogers, A. (2001). Photographic Guide to the Sea & Shore Life of Britain & North-west Europe. OUP. Oxford.
Hayward, P.J. & Ryland, J.S. (eds) (2000). Handbook of the Marine Fauna of North-West Europe (2000 revision). OUP, Oxford.

Further reading

Crothers, J.H. (1997). A key to the major groups of British marine invertebrates. Field Studies 9(1): 1-177. Very useful if you are new to marine invertebrates.
Hayward, P.J. (1988). Animals on Seaweed. Richmond, Slough. For those interested in generally small intertidal species found attached to seaweeds.
Hayward, P.J. (1994). Animals of Sandy Shores. Richmond, Slough. Not used here although Calshot Beach is sandy in places and supports some of the species in this book.
Hiscock, S. (1979). A field key to the British brown seaweeds (Phaeophyta). Field Studies 5(1): 1-44. Useful alongside Hayward (1988).

Pastel predators, fearsomely floral

Those of you who enjoy gardening, or simply looking at flowers closely, may well have seen crab spiders (family Thomisidae) lurking in them waiting for prey. You know the ones - they're often fairly flat compared with more bulbous orb-web spinners, and tend to wait with their legs spread out and bent crab-wise (they can walk sideways) until prey comes and they pounce - none use webs to catch their prey. Many are also well camouflaged, and this is certainly true of Misumena vatia which is found fairly commonly in Britain, particularly in the south. Males are tiny (3-4mm) and quite uniform in colour (mainly brown), but females (the focus here) are larger (9-11mm) and variable in colour - usually whitish, yellowish or greenish, and for this reason are particularly associated with white or yellow flowers, although I have seen a small white female crouching very obviously on a purple Buddleia davidii flower-spike - as a youngster, she obviously had a lot to learn!

Waving, not drowning - M. vatia in a typical posture showing the first two pairs of legs which are used to trap prey.

As this photo above shows, the rear pairs of legs (pairs III & IV) are used to grip the substrate with claw hooks and tufts of hairs ('scopulae'), while the front pairs (pairs I & II) act as traps for prey.

M. vatia hiding in a yellow flower. Note the elongated leg pairs I & II used for trapping prey.

M. vatia lurking in a flower being visited by a bee.

Ambush specialists such as M. vatia have venom which is particularly toxic to prey such as bees, even bumblebees, which are much larger than themselves. To us they are quite attractive and engaging little spiders, but to many other invertebrates they are fearsome foes. When suitable prey arrives at a flower, the spider may do nothing for some time, or may open leg pairs I & II in preparation for attack, sometimes also making subtle realignments to ensure it is accurately facing the potential prey item. When, and only when, the prey is definitely within its grasp is the ambush launched, then once gripped it is bitten and quickly dies. Although I did not see one of these spiders attack a bee, I was lucky enough to witness a similar attack on a hoverfly - the common Marmalade Fly Episyrphus balteatus.

After a quick snatch, the fly is bitten on the back of the neck and feeding commences.

Feeding may go on for some time leaving a dry husk as crab spiders have small jaws/fangs so can't mash their prey.

However, if disturbed this species often darts beneath its flower to hide. In this case, the disturbance was accidental by a benign ecologist, and the spider responded true to form - in this case still cluching its prey which dangled from its jaws, showing the considerable strength often seen in invertebrates.

Although I have looked solely at M. vatia here, crab spiders are an interesting and varied group. Some such as those in the genus Philodromus may chase their prey more actively while others show adaptation of shape as well as colour to aid camouflage, such as the angular-bodied females of Thomisus onustus which is often pink, found on heather and can change colour slowly to match its surroundings. Should I manage to get any good shots of T. onustus, they are likely to appear here...

Here's lookin' at you...

Reference

Roberts, M.J. (1995). Spiders of Britain & Northern Europe. Collins, London.

Spider crabs - spiny substrates on legs

We're all familiar to some extent with crabs and other crustaceans - the shell or carapace, the pointed walking legs, the first pair of legs with pincers and so on. Around the (mainly southern and western) coast of Britain, one large and distinctive species is the Spiny Spider Crab Maja squinado which can have a carapace up to 20cm long (not to mention the long legs), although the specimen below is about half this size. This is a fairly shallow-water species, found sublittorally to about 50m depth, but sometimes also in deep littoral pools low on the shore.

Dorsal view of the carapace showing bumps (tubercles) and spines, including the two larger frontal spines of the rostrum seen spreading apart at the top of the photo. These rostral spines are straight unlike those of M. verrucosa which are curved outwards. Note the growths of other organisms such as seaweeds, hydroids and sponges.

The spines have clear potential as protection against predators, and can also prove uncomfortable to the unwary paddler if a carapace is trodden on (fortunately they are not poisonous like some organisms such as weaver fish) and indeed may hide under loose substrates such as coarse sand. Their ability to hide is enhanced by the range of other organisms that use them as a substrate to grow on e.g. sponges, hydroids and seaweeds - this allows them to blend in with other substrates supporting similar organisms. For those of you who like fairy tales, think about Baba Yaga's walking hut from the traditional Russian story, or indeed the Studio Ghibli animation Howl's Moving Castle!

A close-up of the upper surface of the carapace.

Zooming in on the carapace, the tubercles can be seen to have tufts of bristles - a close look shows that where some have broken off, tiny holes remain in the surface of the carapace. Such bristles or hairs are also seen on the legs following a moult, though these are gradually rubbed off. More of these bristles later...

The inner surface of the carapace.

In contrast to the patchily pinkish, rough outer surface (could this texture be to aid the attachment of organisms?), the inner surface, with no need to be involved in camouflage, is smooth and white. The dimples show that the tubercles are hollow, reducing weight (even so, with their spindly limbs and large bodies, large spider crabs can't support their own weight out of water) while the wrinkled arc shows where muscles and other tissues were attached when the animal was alive.

Another view of the underside; this time some of the points of attachment for the mouthparts and related appendages. The basal segment of one such appendage remains - its pair shows an empty socket.

A close-up of one of the articulations on the underside of the carapace.

The first of these two photos shows the membrane forming part of the joint at the base of the appendage, but some hairs are also visible. The second photo shows such a brush of hairs in more detail. They are simple unjointed structures and are likely to be guard hairs with the function of keeping sand grains and other unwanted material out of delicate joints.

The V-shaped notch between the two rostral spines showing numerous bristles as well as the tiny holes where some are missing.

The spaces between spines around the edge of the carapace show similar bristles. These may again be there to trap unwanted material (and maybe they help with camouflage by breaking up the outline, especially if they collect seaweed fragments and similar), but the crab also has much tinier, finer sensory hairs (not visible here) which also need to be protected by guard hairs. Of course, crabs do not rely solely on sensory hairs - they also have compound eyes on mobile stalks.

One mottled compound eye on its mobile stalk. This mobility means the eye can be tucked away into a notch in the carapace to prevent damage.

A close-up of the eye showing individual lenses and the 'seal' around the edge. Red and green iridescence is also visible just below the centre of the photo.

The base of the eye-stalk again showing the guard hairs which help to protect joints from damage by unwanted materials.

This has been a fairly brief tour of spider crab morphology, even though it covers only the carapace - if I find some during a bout of beach-coming, I may write a follow-up covering legs and other appendages. Until then, enjoy the story so far and we'll see what the tide and strandline bring...


References

Crothers, J. & Crothers, M. (1988). A key to the crabs and crab-like animals of British inshore waters. Field Studies 5: 753-806. Revised version available here.
Gibson, R., Hextall, B. & Rogers, A. (2001). Photographic Guide to the Sea & Shore Life of Britain & North-west Europe. OUP, Oxford.
Hayward, P.J. & Ryland, J.S. (eds) (2000). Handbook of the Marine Fauna of North-West Europe (reprint with corrections). OUP, Oxford.

Hoverfly heaven: summer in a suburban garden

Over the summer I've written a fair amount about the bee species found in our garden - from general bee diversity to a more detailed description of the behaviour of a single, relatively uncommon species. Much of this relates to our attempts to make our garden bee-friendly by providing bee-logs, a wide range of nectar sources and in general a suitably diverse structure. Of course, features like this attract other species groups too and one of these is the hoverflies (Diptera, Syrphidae) which can often be seen visiting flowers.

A 'typical' hoverfly showing yellow and black banding.

Though harmless, many species of hoverfly show 'Batesian' mimicry i.e. features such as yellow-and-black banding which mimic the colour/pattern of potentially harmful organisms such as wasps. This may help deter predators, especially if they have previously been stung by a wasp, though in humans it can cause unnecessary swatting by the entomologically uninitiated...

The common 'Marmalade Fly' Episyrphus balteatus feeding in a day-lily

A head-on view of E. balteatus. Note the eyes meet on the top of the head - this is often a clear indicator that the specimen is a male (and not just in this species); in females the eyes generally don't meet.

Myathropa florea showing the distinctive pale spots and bars on the otherwise dark thorax.

Scaeva pyrastri feeding on Buddleia davidii - note the white 'lunules' rather than yellow bands.

An oblique/side view of S. pyrastri showing the somewhat flattened abdomen.

Syritta pipiens showing the distinctively swollen and toothed hind femur.

 As well as wasp-like mimicry, a number of species mimic bees, including the 'drone-flies' of the genus Eristalis which mimic honey bees (Apis mellifera). 

Eristalis arbustorum (note the golden pubescence) on a dried-out dock (Rumex) plant.

The dark form of Eristalis tenax, one of the honey bee mimics in this genus. The paler form has paler, clearer banding. E. tenax may be found feeding alongside honey bees and can look very similar. The larval forms are very different though, with Eristalis producing the 'rat-tailed' maggots (named after their long posterior breathing tubes) which can be found in stagnant water.

Other species can be very different again. Many hoverflies are small and dark (such as Cheilosia), while some are bumblebee mimics such as Volucella bombylans and Eriozona syrphoides which is likely to be a fairly recent (1950s) colonist associated with spruce.

Merodon equestris, a mimic of hairy bee species with very variable colouration from almost all black to extensively brown and/or pale.

Rhingia campestris showing the long 'snout' in side view - a characteristic of this genus.

Of cours, it's not all about the flowers - hoverflies need to make sure there are plenty of their kind around next year. So, I shall leave you with a couple of pics of them doing exactly this. Feel the love!

A pair of Helophilus (probably H. pendulus).

A pair of Sphaerophoria scripta trying the back-to-back position. The female's on the right.

Reference

Stubbs, A.E. & Falk, S.J. (2002). British Hoverflies. BENHS, Reading.

Further reading (if you want to know about the larvae)

Rotheray, G.E. (1993). Colour Guide to Hoverfly Larvae (Diptera, Syrphidae). Derek Whiteley, Sheffield.