There are 8 species of Meloe (the true oil beetles) on the British list. Until a few years ago, five of them were regarded as probably extinct with no records for several decades but two have been recently rediscovered. The best sources for identification of the five extant species are John Walters’ website, and Buglife’s Oil Beetle ID Guide (updated 2013 version, also by John Walters).
The Short-necked Oil Beetle M. brevicollis went completely unrecorded from 1948 until its rediscovery in South Devon in April 2006. The Mediterranean Oil-beetle Meloe mediterraneus was found at the same site shortly afterwards but initially identified as Rugged Oil-beetle Meloe rugosus. It took some careful observations by John Walters to confirm that this was actually a population of mediterraneus, unrecorded in Britain since some time in the 1800s!
Is there any hope of rediscovering the three extinct species in Britain? On the basis of these discoveries in South Devon, there must be hope that the others could still be persisting unnoticed somewhere. Obviously nobody using Buglife’s ID guide is going to rediscover any of the extinct species as they’re not included in that guide. For those wishing to remain vigilant for all the options, the best identification guide is Alex Ramsay’s paper in British Wildlife (Vol 14, No 1 (October 2002); back issues still available for purchase) with artwork by Richard Lewington. Alex’s paper includes all 8 species (and a ninth, M. decorus, with a single British record from Gloucestershire in 1870 regarded as a non-established introduction). Beware that Alex’s paper oversimplifies the separation of the two most frequent species (Black Oil Beetle M. proscarabaeus and Violet Oil Beetle M. violaceus). They are a genuinely difficult pair and the best way to identify them is to look at John Walters’ webpage.
If you prefer something more detailed and can read German, this book is apparently excellent:
Lückmann, J., Niehuis, M. (2009). Die Ölkäfer (Meloidae) in Rheinland-Pfalz und im Saarland. GNOR.
The 1st-instar larvae of meloids are known as triungulins (NOT ‘triangulins’). The word derives from Latin tri- (three) and ungulus (toenail) and refers to a distinctive feature of these larvae which is that they have three-hooked tarsi, presumably an adaptation to help with the critical challenge they face – having to grab onto a female bee and cling on long enough to get back to her nest. Surprisingly, the five extant British Meloe all have quite different triungulins, which can be identified using John Walters’ triungulin page. There is also a key to triungulin larvae of all British meloids except for M. mediterraneus by van Emden (1943) and they’re not too difficult.
In fact, recording triungulins on flowers or on bees is probably the best way to make new discoveries in our fauna. I added Short-necked Oil Beetle M. brevicollis to the Irish list from Cahore dunes, Co. Wexford just two months after it was rediscovered in South Devon. It was a completely fortuitous discovery: I only collected one bee at the site, a voucher of Colletes floralis, and only noticed that there was a triungulin on it some time later. When Darren Mann identified it as M. brevicollis, I was gobsmacked, to say the least!
In a similar vein, Roger Booth found a triungulin on a bee from Kent, possibly of Stenoria analis, which would be new to Britain. Stenoria analis has expanded its range northwards in western Europe recently, following the expansion of its host bee Colletes hederae. The bee was first recorded in Britain in 2001 and BWARS have given it an excellent webpage. There is a good paper on the association between bee and beetle online here with some excellent photographs. It should only be a matter of time before S. analis is confirmed here too.
van Emden, F.I. (1943). Larvae of British beetles. IV. Various small families. Entomologist’s monthly magazine, ?78?(1943), 209 – 223 and 259 – 270.