Pelophila borealis (Paykull, 1790)
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ADEPHAGA Clairville, 1806
PELOPHILINI Kavanaugh, 1966
PELOPHILA Dejean, 1821
The only genus of the Pelophilini Kavanaugh, 1966, Pelophila includes 2 species; the present species has a circumpolar distribution while P. rudis LeConte, 1863 is Nearctic, both are cold-adapted and arctic or sub-arctic in distribution. P. borealis occurs mostly within the Arctic Circle in Siberia, Alaska and Northern Canada but extends south into northern Scandinavia and the UK. Here it is widespread in the north and west of Ireland, occurs in Orkney and Shetland and there is a single mainland population at Glen Affric, Inverness. The typical habitat is sparsely vegetated silty or clay soils on lake and slow river margins, more generally in highland situations but in Ireland it is a lowland species not occurring above 200m; the Scottish population occurs in a vegetated flush at 840m while in Scandinavia it occurs at high and low elevations and in Alaska it occurs around densely vegetated margins on tundra and also at high altitudes. The Irish populations are in decline and that at Lough Erne appears to have vanished, probably as a result of climate change as the habitats have not been degraded, and so it is classed as a priority species. Adults occur year-round and are active between April and August; they are fast moving and cryptic and so easiest to observe on open marginal areas between patches of vegetation, when disturbed they run and hide under stones etc. or in cracks in the substrate. Mating occurs in the spring and the adults die-off during early summer, new-generation adults occur from mid-summer and go on to overwinter; in northern Norway they have been found overwintering at 1200m in marginal sediment covered by 60cm of ice and periodically flooded from September to June, but despite these apparently harsh conditions the species is cold-adapted and the temperature rarely falls below -4 Celsius.
Among the UK fauna Pelophila might only be confused with the similarly sized Blethisa multipunctata (Linnaeus, 1758) but here the front tibiae have only a single large spur on the inner-apical angle. Pelophila is a medium-sized carabid, 8.3-13mm with a convex dorsal surface, long legs and distinctively sculptured elytra. Most specimens are dark, black to brown with a metallic bronze reflection but strikingly green or blue specimens also occur. The vertex is smooth and unpunctured and there are irregular longitudinal wrinkles beside the eyes, the mandibles large, curved and sharply pointed and the antennae long and generally black although some or even all segments may be dark or pale brown. The pronotum is cordate and very transverse with a transverse punctured depression behind the anterior margin, explanate and punctured lateral margins, sharp posterior angles and 2 wide and deep basal fovea. Elytra characteristic; each with 10 striae from the base almost reaching the apex and lacking a scutellary striole (this is present but continued to the apex), and with 2 series of large setiferous fovea; 5 or 6 in the third interstice and 3 in the fifth. The legs are dark, black to dark brown, although in some continental specimens they are red with narrowly darkened ‘knees’, the front tibiae lack an antenna-cleaning notch, and all tibiae have 2 large spurs at the inner-apical angle. The basal front-tarsal segments are dilated in the male.