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Bembidion caeruleum still hanging on

Pete Akers, warden of the Dungeness RSPB reserve, found a single specimen of the very elusive carabid beetle Bembidion caeruleum at ‘The Honeypot’, a bay on the north-west edge of Burrow’s Pit (TR06771854) on 22nd April 2009. The Honeypot is one of the best remaining areas of quicksand on the reserve, or it was when I was last there in May 2005. The soft sediments on the Dungeness pit margins are declining fast now that gravel extraction has completely ceased and the dreaded Crassula helmsii has become established. Access to the Honeypot is strictly by permission of the warden.

Bembidion caeruleum was first identified from Britain by holidaying Norwegian coleopterist Sindre Ligaard who found about 15 specimens by torchlight at Dungeness RSPB reserve on the night of 22nd July 1999 (Telfer, 2001). An earlier record of two specimens from nearby Brett’s Pit on 3rd May 1989 was then unearthed. I’ve since spent several nights torching at Dungeness and only seen a single B. caeruleum: one collected by Brian Eversham on some treacherous quicksand (now gone) at the north end of the ARC pit on 18-19 May 2000. Of the several other coleopterists who have worked the pit margins at Dungeness in the last decade, to my knowledge only John Paul has found B. caeruleum: one on 11th August 2002.

So Pete’s 2009 record shows that B. caeruleum is still present at Dungeness. Since British coleopterists are having such difficulty finding it, perhaps it’s time we invited the Norwegian back to show us how it’s done?!

Reference

Telfer, M. G. (2001). Bembidion coeruleum Serville (Carabidae) new to Britain and other notable carabid records from Dungeness, Kent. The Coleopterist, 10, 1 – 4. [Note that the species is now known, correctly, by the original spelling ‘caeruleum‘ rather than ‘coeruleum‘.]

Charismatic microfauna

Some of the smallest beetles are ‘must see’ species. Here are three of the best.

But for its wonderful name, Microdota liliputana or as Roger Key once dubbed it, “The Lilliputian Micro-dot Beetle” would be just another member of the obscenely speciose Aleocharinae subfamily of staphylinids, albeit quite a small one (1.6 – 1.9 mm). However, I have wanted to see it since I first heard about it maybe 15 years ago, and now I have. It was named by Brisout in 1860, 134 years after the publication of Gulliver’s Travels. This female flew into a pan trap in the reedbeds at the RSPB’s Ham Wall reserve in June/July 2009 – the first for Somerset. The traps were run by Donna Harris and Anna Doeser as part of a project on reedbed management for Bitterns.

Sphaerius_acaroides

Sphaerius acaroides (0.7 mm) probably ought to be called “The Full Stop”, though to be fair there are quite a lot of candidates for that name. It is, taxonomically, the most unique British beetle, being our only member of the sub-order Myxophaga. All our other beetles are either in the Adephaga or the Polyphaga. It has been recorded from a scatter of sites north to Westmorland (map here) but in recent decades has only been found on the wonderful undercliffs at Eype, Dorset and is listed as a Red Data Book species. The trick is to find trickles of water, agitate the mossy vegetated margins knocking any Sphaerius into the water where they become a lot easier to spot and then try to pick them off before they float away downstream. As the name implies, they look very like mites, but have a beetle’s gait. It must be overlooked elsewhere in the country, surely? Finding one is challenging but as the photo shows, carding one with all its appendages on show is even more so!

Finally, Britain’s smallest beetle at 0.55 – 0.65 mm is the ironically named Nephanes titan, or as I like to think of it “The Titan”. It is one of the feather-winged beetles, family Ptiliidae. It’s not supposed to be a rare species but I have only ever noticed it once, while sieving the top layers of a steaming manure heap in the woods north of Isle of Wight Farm, Denham in November 2008.

Ignore the scale bars on the pictures – something went wrong!

Driller killer: the solution … ?

Those who’ve been in contact fall into two camps: those who think the holes were probably caused by another mollusc, and those who think they were caused by a beetle. But tellingly, all the mollusc experts so far think that beetles of some sort must be responsible, and two have noted that they’ve seen holes like this in terrestrial snail shells in the Mediterranean.

As Richard Wright and others have kindly pointed out, there’s a 2004 book on “Natural enemies of terrestrial molluscs” with a detailed chapter on Coleoptera as predators of terrestrial gastropods by Bill Symondson of Cardiff University. Bill’s response must therefore be the most authoritative that I’ve received but is still a guess: “I would guess that these are the exit holes of drilid beetles, that parasitise many species of snails”.

The great thing about Bill’s response is that it has turned the mystery on its head – it’s not about what’s trying to get in but what’s trying to get out! In support of the parasite theory: (1) there are 5 separate holes – why would a predator need more than one?, (2) the holes are quite evenly spaced as they might be if 5 parasites had partitioned up the snail between them, and (3) one of the holes is right by the mouth aperture so there’s no way it was the easiest route of attack to get IN to the shell.

So, given that Drilus flavescens is the only drilid on the British list and it has been recorded not too far away to the south in Berkshire and Oxfordshire (map here), can we add it to the Buckinghamshire list? Maybe.

Andrew Duff dug up another interesting lead here. This person has lots of Garden Snail Cornu aspersum (formerly Helix aspersa) shells in their garden with one or two neat circular 4mm holes in them. Nobody on the wildaboutbritain forum seems to know what’s caused them but whatever it is must be the same beast that drilled the Grangelands Helix pomatia. However, the garden in question is in Lincolnshire! I could believe that Drilus flavescens exists at Grangelands – a superb calcareous grassland just north of the known range. But I find it harder to believe that Drilus exists in a garden in Lincolnshire!

For a definitive answer, Julia’s going to try and breed the parasites out in 2010.

Meanwhile, thanks to all those who’ve been in touch and if anyone has further suggestions, I’d be glad to hear them.

Driller killer: what eats Edible Snails?





Alison Woods and Julia Carey found this empty shell of Helix pomatia, the Roman Snail or Edible Snail, at Grangelands, Buckinghamshire on or shortly before 18th February 2009. Julia is well acquainted with this population of the snail and has never seen one, before or since, with neat circular holes in the shell, despite looking at lots of shells. What made those holes? I’ve been puzzling over the specimen for the best part of a year without coming any closer to an answer. Can you help?

There are 6 circular holes in the shell, each of 4 mm diameter. I’m guessing they were made by a predator but why not attack the exposed body of the snail at the mouth of the shell rather than breaking through the shell wall?

The damage to the Helix shell is reminiscent of that caused to bivalves by the marine necklace shells so my best guess is that this Helix was attacked by another mollusc, perhaps the Leopard Slug Limax maximus which is known to be a predator of other slugs at least.

Any and all suggestions gratefully received!

Mystery Malthodes new to Britain?


The photo shows a small female Malthodes (Cantharidae) captured in a reedbed at Stodmarsh (TR 21924 62059), East Kent (VC 15) between 1st and 30th June 2009. It is a flightless beetle with very short elytra and hind-wings reduced to tiny stubs. At first sight I thought it was Malthodes lobatus, known in Britain only from three females found by Max Barclay near Brighton on 24 July 2002. However, from the photograph (see here) in Barclay and Kopetz (2003) and text therein, my specimen is clearly different: larger (1.5 mm to tips of elytra, 2.8 mm to tip of abdomen), longer elytra (just beyond the hind coxae), distinctly more elongate antennae.

Could my specimen be a brachypterous form of one of the other small British Malthodes? I don’t think so. I’ve compared it to female M. pumilus and it is larger, more robust, with less elongate elytra and distinctly more elongate antennae. Compared to female M. crassicornis, it also has more elongate antennae and a very different pronotum shape.

So I’m thinking something new to Britain? If anyone can put a name to it or offer any pointers, I’d be very grateful.

30th Nov 2010: I have now heard from Andreas Kopetz (pers. comm. 9th Feb 2010) and Vladimír Švihla (pers. comm. 23rd Nov 2010) and have tried to identify my specimen for myself at the Natural History Museum. It looks like I am not going to be able to identify this beetle: if it had been a male there would be no problem but females cannot always be identified. Although the Stodmarsh Malthodes shows some striking differences from M. pumilus and M. lobatus, there don’t appear to be any other tiny flightless Malthodes on the continent which might occur in Britain. So, as Švihla has suggested, this could be an extreme variation of Malthodes lobatus; as this is a flightless species, it could evolve distinct local ecotypes. The other possibilities, that it is a species unknown in Europe, or unknown to science, seem less likely.

Males of M. lobatus (and M. pumilus) are very rare, much less frequent than the females. I think the males have wings and can fly so I am thinking of running a flight interception trap at Stodmarsh to try and find one. Males of M. lobatus are recorded as having been found between mid-June and early July.

Thanks to Darren Mann and James Hogan at OUMNH for discussion and allowing me to use their photo-montage equipment.

Reference:
Barclay, M.V.L. and Kopetz, A. (2003). Malthodes lobatus (Kiesenwetter) (Cantharidae) new to Britain. The Coleopterist, 12(3), 97-100.