Status Overview
The leaf beetle (Chrysomelidae), Bromius obscurus (Linnaeus, 1758) was given a Great Britain (GB) Rarity Status of ‘Nationally Rare’ and a GB IUCN threat category of ‘Critically Endangered’ in the 2014 review of the scarce and threatened leaf beetles of Britain (Hubble, 2014).
Rationale for IUCN classification (Hubble, 2014)
According to Hubble (2014) it is ‘currently only recorded from one site in Scotland after a marked historic decline. It has an Area of Occupancy of less than 10km’. However, this assessment needs adjustment as it was incorrect. The continued presence of the species at Rushton Spencer had not been taken into account, so the Scottish record was an increase on the known distribution. There has not been a marked decline as there were very few records to begin with.
Summary of records
Bosley, Cheshire (VC58): 1979, 1981, 1992.
Rushton Spencer, Staffordshire (VC39): 1982, 2008, 2013, 2019.
Scunthorpe area, Lincolnshire (VC54) 2013, 2014, 2015, 2018, 2019, 2021
Jupiter reserve, Stirlingshire (VC86): 2018.
Brereton Heath, Cheshire (VC58): 2019, 2020.
Swettenham, Cheshire (VC58): 2020.
Mow Cop, Staffordshire (VC39): 2021.
Despite the mention of possible Lincolnshire records of B. obscurus by Stephens (1831&1839), until 2013, it had only definitely been recorded from either side of the Cheshire (VC58) / Staffordshire (VC39) border at Bosley and Rushton Spencer (Fig. 2). In June 2013 Charles Barnes recorded it from Crosby Grange in the Scunthorpe area in Lincolnshire and it has since been recorded in the area many times by the same and other recorders (Barnes, 2021). In 2018 there was a surprising record from the Jupiter Reserve in Stirlingshire which is approximately 200 miles (320 km) from the Cheshire sites. The following year there was a serendipitous find of the beetle by David Bentley at Brereton Heath, which added a site to the known Cheshire distribution, and a visit to the same site by D.A.S and Clive Washington confirmed continued presence on 27th May 2020. A few days later C.W. found the beetle at Swettenham, which is very close to the Brereton site. In 2021 a find from the Mow Cop area in Staffordshire, was reported on Facebook by Simon Cowley. Once again, the location is very close to the Cheshire / Staffordshire border. Figure 2 shows the current British distribution and further information on targeted fieldwork is presented in Stenhouse (2021).
Figure 1. The cluster of records either side of the Cheshire / Staffordshire border
Figure 2. Known distribution of Bromius obscurus in Britain
Habitat
The habitat of B. obscurus is basically any area that contains stands of willow-herb, particularly rose-bay Chamaenerion angustifolium (L.) Scopoli. This may include dismantled former railways, grassland, woodland rides and brownfield sites. The beetle is probably a good flier as it has prominent shoulders to the elytra suggesting well developed flight muscles, and specimens from Rushton Spencer possess complete wings. It is likely that it can move easily between suitable patches of habitat.
Recording / Identification
Identification of B. obscurus is quite straightforward (Fig. 3). The beetle is 6mm in length and quite ‘dumpy’, with very square shoulders to the elytra, completely black, and covered with a fine recumbent pubescence. The appendages are also black except for the first four segments of the antennae which are mainly orange, the first segment being orange ventrally and black dorsally, the 2nd and 3rd completely orange, and the fourth orange at the base and black in the second half. There are no similar species.
The foodplant is a useful guide and any patches of willow-herb should be examined (Fig. even those that are swamped by other vegetation (Barnes, 2021). The adult beetle is easily seen as it sits on the upper leaf surface but may drop off if it detects a shadow. It can be collected by sweeping a likely stand of the foodplant. The likelihood of its presence is revealed by the feeding signs, which are typically linear, distinctive and diagnostic as there are no other species that feed on willow-herb in this fashion (. The larvae of B. obscurus cannot be practically recorded as they are subterranean, feeding on roots of the foodplant and are the stage that overwinters in litter, emerging as the adult in the following spring.
There are several recent publications containing keys that lead to identification of B. obscurus including Hubble (2012) and Duff, A.G. (2016), although the information given above should suffice.
Figure 3. Bromius obscurus from Rushton Spencer on 5 August 2019 D.A.S. Photograph by Bill Urwin.
Figure 4. Habitat of Bromius obscurus at Rushton Spencer 30 June 2013. D.A.S.
Habitat
Figure 5. Bromius obscurus feeding signs on leaves taken from Rushton Spencer on 5 August 2019. D.A.S.
Conservation
There are no specific measures in place currently to protect B. obscurus. One of the Cheshire sites it has recently been recorded from, Brereton Heath, is a Local Nature Reserve and as the beetle was recorded during a survey the management are presumably aware of its presence and status. Repeat visits to the Rushton Spencer site by several recorders over a long period confirm both a stable habitat and population.
On sites where B. obscurus is present, any stands of willow-herb should be maintained. The encroachment of scrub is undesirable and should be prevented to maintain open conditions.
The number of known 10 km squares recorded for the beetle has increased and further recording effort is likely to result in a more detailed understanding of the distribution and requirements of this enigmatic species.
Acknowledgement
Clive Washington is thanked for his help and companionship during fieldwork and Gary Hedges for arranging a Tanyptera Trust grant. The maps were created using DMAP for Windows, Version 7.7 developed by Dr Alan Morton.
Further Information
Brereton Heath Local Nature Reserve page on Cheshire East Council website
UK Beetles Species Account for Bromius obscurus
References
Barnes, C. (2021). The distribution of Bromius obscurus (Linneaus) (Chrysomelidae) in North Lincolnshire. Coleopterist 30 (2): (in press).
Duff, A.G. 2016. Beetles of Britain & Ireland. Vol 4: Cerambycidae to Curculionidae. A.G. Duff (Publishing).
Hubble, D. S. 2014. A review of the scarce and threatened beetles of Britain. The leaf beetles and their allies Chrysomelidae, Megalopodidae and Orsodacnidae. Species Status No.19. Natural England Commissioned Reports, Number 161.
Stenhouse, D.A. 2021. The status and distribution of the leaf beetle Bromius obscurus (Linnaeus, 1758) in Cheshire in 2019 and 2020.
Stenhouse, D.A. 2020. Bromius obscurus (Linnaeus) (Chrysomelidae) extant in Staffordshire (VC 39) and a summary of British records The Coleopterist 29(2): 93-95.
Stephens, J.F. 1831. Illustrations of British Entomology. Mandibulata Vol. IV. London: Baldwin and Cradock.
Stephens, J.F. 1839. A Manual of British Coleoptera or Beetles. London: Longman, Orme, Brown, Green and Longmans.
