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Abstract.  1. Ciid beetles typically live and breed in the fruiting bodies of lignicolous basidiomycete fungi. This study was undertaken to address the lack of an objective examination of patterns of host use by ciids. 2. Cluster analysis of ciid host‐use datasets from Britain, Germany, North America, and Japan, and subsequent cross‐dataset comparisons, demonstrated the existence of ciid host‐use patterns of wide geographical occurrence. These patterns were formalised as ciid host‐use groups. 3. Six Holarctic ciid host‐use groups, and two host‐use subgroups, were identified, and are described. Each host‐use group comprises an assemblage of fungal genera and the breeding ciids that it supports. Each taxon belongs to only a single host‐use group, but may be associated with several members of that group. There is a strong tendency for closely related taxa to belong to the same host‐use group. 4. It is suggested that ciid host‐use groups are defined ultimately by host chemistry, with the ciids that belong to a particular group recognising, and responding positively to, emitted volatiles characterising the fungi belonging to that group. 5. The idea of the host‐use group bears comparison with the concepts of niche and guild, but is not equivalent to either. 6. Ciid host‐use groups have a valuable role to play in underpinning future studies of ciid ecology, also the systematics of both ciids and their fungal hosts.

Since its accidental introduction to southeast England during the nineteenth century, the invasive Australasian fungivore, Cis bilamellatus, has spread across England, Wales and Southern Scotland. Recently it has been recorded from Ireland, the Channel Islands and north-west France. On mainland Britain, an establishment phase spanning an estimated maximum of 45 years was followed by biphasic range expansion comprising a slow start of 1.6 km year -1 between 1910 and 1930, followed by 40 years of approximately linear spread of 13 km year -1 . Northwards expansion now appears to be limited by sub-zero winter temperatures and is no longer apparent. Comparison with historic records of native ciids shows that this range expansion is genuine, rather than an artefact of recording effort or bias. It has no doubt been facilitated by C. bilamellatus' ability to exploit a wide range of sometimes under-used fungal resources, by its favourable rate of increase, by its tolerance of both wet and dry conditions, and by a low rate of parasitoid attack. Although there is the potential for direct and indirect interaction between C. bilamellatus, native ciids and their shared parasitoids, the current ecological impact of C. bilamellatus appears to be low. It seems likely that C. bilamellatus will spread through Europe, limited primarily by resource availability and low winter temperatures.

Social Hymenoptera have been relatively little studied in terms of conservation genetics even though their sociality and omplementary sex determination potentially influence the interaction of genetics with extinction risk. Using microsatellite markers, we investigated the social and genetic structure of nests and populations of the Black Bog Ant Formica picea at four sites in the UK, where this habitat specialist has a localized and fragmented range. Nests were weakly polygynous (effective queen number, 4–27 per nest) with low orker relatedness. Isolation by distance tended to be present within sites, indicating limited dispersal, but inbreeding was rare. The four study sites fell into three main populations (two in South Wales, one in southern England). We conclude that, although UK F. picea populations are not at immediate risk from genetic factors, their limited dispersal abilities at both within- and between-site scales should inform conservation management decisions