A review of Callicerus sp. (Col., Staphylinidae) in the English midland region
Observing the athetine rove beetle Callicerus rigidicornis (Erichson, 1839) in flight on the Birlingham floodplain during April 2012 reminded me how scarce and poorly understood this genus of beetles is in Britain. Most British overviews of Coleoptera confirm the scarcity of Callicerus spp. which occur mostly to the south of the Pennines. It seems opportune to review what is known of Callicerus in the midland area and make some assessment of its conservation status.
Two species of Callicerus occur in Britain and these are by far the most widespread of the seven European species. The smaller Callicerus obscurus Gravenhorst, 1802 attains some 3.0 mm in length whilst large female C. rigidicornis may occasionally exceed 5.0 mm in length. Males of C. rigidicornis may be distinguished from females by the short keel on their first abdominal tergite, a feature lacking in male C. obscurus. The males of C. obscurus can be distinguished by their conspicuously elongate apical and penultimate antennomeres, much more so than those of the females.
Callicerus obscurus Gravenhorst, 1802
Callicerus obscurus is known to me from eight Worcestershire and two Warwickshire specimens. These include female spring dispersants from February to April (the one in flight at Broadway on the rather early date of 23 February 1990 coincided with one of the warmest February days on record there when the temperature reached 19oC). Only one male has been observed, in flight at Little Comberton on 30 April 2010, indicative of male spring dispersal.
Ecology. In Worcestershire, female C. obscurus have been observed wintering in litter and moss in ancient escarpment woodland blocks on the south side of Bredon Hill where at Westmancote three examples were found by woodland springs during March 1992. During 1992 and 1994 examples were found amongst winter wheat on arable land at ADAS Drayton, Warwickshire (Corbett & Whitehead, unpublished; cited by Lane, Wright & Forsythe, 2002) where Jurassic clays inhibit water transmission. This range of habitats is mirrored exactly by Duff (1993) citing seven records from Somerset spanning a period of 107 years. Atty (1983) could cite only two Gloucestershire records including a 1914 example also in a well-incised wooded Cotswold Hill valley. A relatively clear picture can therefore be reconstructed of a localised, possibly under-recorded insect with a preference for somewhat humid closed-canopy woodland shrouding water bodies or artesian drainage.
Regional records. Single specimens except where stated.
Warwickshire (Corbett & Whitehead, unpublished; cited by Lane, 2002).
Drayton ADAS, SP15, 40 m O.D., in winter wheat on arable farmland, 9 March 1992 and 9 June 1994 (crop in ear).
Broadway, SP03, 91 m O.D., wooded valley, in flight, 23 February 1990.
Westmancote, SO93, 130 m O.D., woodland floor litter, 9 March 1992.
Westmancote, 145 m O.D., near or at springs in ancient woodland, 13 March 1992, 16 March 1992, 18 March 1992 (2).
Westmancote, 145 m O.D., scrub woodland, at weeping cut of freshly 'ringed' ash tree, 10 May 1994.
Little Comberton, SO93, 30 m O.D., in flight near hill stream, 30 April 2010.
Callicerus rigidicornis (Erichson, 1839)
All three Worcestershire specimens of C. rigidicornis known to me are females encountered during their spring dispersal; the records range from the Cotswold Hills to the Malvern Hills implying that the species is localised but widespread. It should not be presumed that this dispersal is long-distance or anything other than local.
Ecology. In France C. rigidicornis is most usually associated with leaf litter in deciduous woodland (M. Tronquet, in litt., 24 April 2012) and there seems little doubt that this species is somewhat hygrophilous like its congener and close relatives in the genus Aloconota; the affinity with Aloconota is evident from the structure of the female genitalia. In Worcestershire records range from 13 m altitude at Birlingham to 300 m altitude in the Malvern Hill's Happy Valley. This last, nectaring on flowers of gorse Ulex europaeus L., and the one from Broadway were both in wooded valleys. The Birlingham specimen may be associated with plantations of hybrid poplar, which are now mostly felled and although not colline it is located in a valley bottom. An association with sheltered woodlands is confirmed by Atty (1983) who recorded a Gloucestershire specimen at Toadsmoor near Middle Lypiatt during 1914. Given what is now known, the single Warwickshire specimen found by Professor F. W. Shotton at Shuttington during May 1966 is likely to have dispersed from humid woodland by the pools at nearby Alvecote. Callicerus rigidicornis is not cited by Duff (1993) and neither species is cited by Tomlin (1949) or Hallett (1954) for Herefordshire or by Darby (2009) for Wiltshire. According to Sharp (1908) C. rigidicornis was noted at sea-level on the estuarine banks of the River Mersey. This may reflect a greater tolerance of exposure in the west of the country, a well-known phenomenon in a number of more usually woodland beetles but in the midlands neither C. rigidicornis nor C. obscurus can be regarded as primary floodplain species (Lott, 2009; Whitehead, 1992). In the midlands C. rigidicornis is likely to favour damp or somewhat closed-canopy broadleaved woodland and is up-to-now unknown on arable farmland.
Regional records. All single specimens.
Broadway, SP03, 91 m O.D., partially wooded valley, in flight, 15 May 1985.
Malvern Hills, Happy Valley, SO74, 300 m O.D., wooded valley, nectaring at flower of gorse Ulex euoropaeus L., 28 April 2007.
Birlingham floodplain, SO94, 13 m O.D., in flight, 22 April 2012 (specimen 5.2 mm in length).
Conservation status of Callicerus spp. The inclusion of beetles in U.K. Nature Conservation 12:2 is warranted on the criteria of their frequency and distribution (Hyman, 1994); Callicerus is excluded from that text. Widespread localised species may nonetheless diagnose sites and situations which reflect clearly on special or ancient landscape features and it is my view that Callicerus, like various other athetine rove beetles, belongs in this category.
Some of these findings arose during research projects for ADAS Drayton, Warwickshire and the Kemerton Conservation Trust, Worcestershire. Marc Tronquet kindly summarised knowledge of C. rigidicornis in France.
Atty, D.B. 1983. Coleoptera of Gloucestershire. Cheltenham, published privately.
Darby, M. 2009. Wiltshire beetles; history, status, distribution and use in site assessment. Malthouse Books, Salisbury.
Duff, A.G. 1993. Beetles of Somerset. Taunton: Somerset Archaeological and Natural History Society.
Hallett, H.M. 1954. The Coleoptera of Herefordshire: first supplement, pp. 279-282 in: Transactions of Woolhope Naturalist’s Field Club, Hereford.
Hyman, P.S. (revised Parsons, M.S.) 1994. A review of the scarce and threatened Coleoptera of Great Britain 2. UK Nature Conservation 12. Peterborough: Joint Nature Conservation Committee.
Lane, S.A., Wright, R.J. & Forsythe, T.G. 2002. An atlas of Warwickshire beetles. Warwickshire Biological Records Centre.
Lott, D.A. 2009. Rare beetles from the lower Soar valley in Leicestershire and Nottinghamshire. British Journal of Entomology and Natural History 22:217-233.
Sharp, W.E. 1908. The Coleoptera of Lancashire & Cheshire, pp. 1-75. Lancashire & Cheshire Entomological Society.
Tomlin, J.R. le B. 1949. Herefordshire Coleoptera 1. Woolhope Naturalist’s Field Club, Hereford.
Whitehead, P.F. 1992. The floodplain Coleoptera of the River Avon, Worcestershire, England, with provisional diagnoses of ancient assemblages. Elytron 6:15-33.