Includes 10 British species; Calyptomenus dubius (Marsham) and nine species of Clambus.
These are tiny beetles, less than 2mm in length, convex oval and of a distinctive appearance and so not likely
to be confused with any other group. The head is about as wide as the very transverse pronotum in Calyptomenus,
relatively narrower in Clambus but of the same distinctive form with the eyes placed on the lateral
angles (Calyptomenus) or quite near (Clambus). Antennae ten segmented with an abrupt two segmented club,
inserted on front margin of head near inside margin of eyes. Upper surface pubescent and very finely punctate,
elytra without striae. Legs delicate and relatively long, tarsi 4-4-4 without any lobed segments.
Although morphologically distinct as a family, specific identification can be very difficult and the group is best left until some experience is gained. Calyptomenus can be separated by the wider head, about as broad as pronotum, with the eyes placed on the lateral angle and with golden pubescence covering the upper surface. The antennae are narrower than in Clambus and there are six visible sternites, five in Clambus. In Clambus the eyes are situated inside the lateral angles a short distance from the edge and in some cases their position relative to the angle is diagnostic. Colour is of very little use but generally, in mature specimens, Calyptomerus is lighter, yellow to pitchy yellow, while Clambus species are darker, black or almost so with pronotal margins variously lighter.
Calyptomerus is widespread through England and lowland Scotland (NBN) and may be found among dying vegetation, often in numbers (Johnson, 1966).
Two species of Clambus, pubescens Redtenbacher and armadillo (De Geer), are readily separated of from the rest by the presence of relatively long and obvious pubescence on the pronotum and elytra. In pubescens the elytra are strongly punctate close to the apical angle while in armadillo they are smooth. Both species are common and widespread and may be identified with confidence so providing the opportunity to become familiar with the group.
With one exception (discussed below) our other species of Clambus have much shorter and more sparse pubescence, giving the appearance of being glabrous. Identification depends upon careful examniation of some very subtle characters and high magnification, at least X60, coupled with good lighting are essential. Surface structure eg of the femoral plates, and pubescence eg on the clypeus are generally diagnostic but this group requires great care and some time should be spent aquiring a series of specimens and examining these at length until familiarity is gained. Male genitalia are diagnostic and will generally need to be examined for confident identification, these beetles are tiny and so dissection would at first be a daunting prospect but be assured that with a little experience the process is straightforward. For more frustrating than dissection is trying to set these species to a good, ie aesthetically pleasing, standard but, apart from the two species with long pubescence, this is neither necessary nor sensible as examination of both the upper and the lower surfaces is needed for determination, it is far better to mount the specimen on its edge on a card point. In life these species are able to roll into a ball and sometimes they remain so after death and so will need to be straightened out, this easiest done by placing the specimen on a small piece of crumpled wet tissue under the microscope at X20 and using two fine pins, gently straighten the specimen from below, at this point an antenna or two and a few legs can be teased out and the specimen transferred to spot of gum on a card or point. Johnson (1966) recommends boilng water rather than ethyl acetate as a killing agent as this will avoid grease on the surface of specimens which can obscure fine detail. The RES handbook by Johnson is essential for identification purposes, with one exception all species are keyed in detail and aedeagi are figured.
Joy's key should not be used; Clambus couplet 1(4) separates off the more pubescent species,pubescens and armadillo, which are then dealt with using comparative features including colour. Beyond this only two species are given minutus Sturm and punctulatum Bech., both of which have been split.
Clambus simsoni Blackburn was added to the British list by Johnson (1997) from specimens found in Wales, this native Australian species was also new to europe (from France, 1993). The elytral pubescence of simsoni is intermediate between the dense and long and the short and sparse types. Johnsons's 1997 paper, which gives a detailed description and aedeagus drawings of simsoni, along with the 1996 handbook will allow the British species to be identified.
Clambids are found among decaying vegetation generally and grass tussocks through the winter. They are best collected by sieving likely samples into bags for extraction and examination under a low power microscope. Adults roll up and remain motionless when disturbed and so might be mistaken at a glance for the shiny black mites which can be very common among such material. Most habitats are worth sampling eg Calyptomenus and Clambus pubescens are local but widespread species of grassland and decaying vegetation generally whereas C.armadillo and C.evae Enrody-Younga are associated with wetland habitats. Much interseting information on the bionomics of British species is given in a review by Johnson (1972)
Unlike several other groups of tiny beetles the clambids are ideal for recording and studying; they are instantly recognisable as a family, there is adequate literature in English available to enable identification of the species and with a little effort at least some of the widespread species should be found. Beyond this there is the satisfaction of being able to deal with tiny species that are not often featured in popular works on insects.
Johnson, C. 1977. Clambus simsoni Blackburn new to Britain, with notes on its wider distribution. Ent.Mon.Mag. 133:161-164
Johnson, C. 1992. A bionomic reveiw of the British Clambidae. Ent. Gazette 43: 67-71