Drusilla canaliculata (Fabricius, 1787)
POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
ALEOCHARINAE Fleming, 1821
LOMECHUSINI Fleming, 1821
Drusilla Leach, 1819
This very widespread species is generally common from lowland to subalpine altitudes across the whole Palaearctic region from Portugal to the far east of Russia and north to the UK and Fennoscandia, it has become established in the United States and Canada following introductions. Here it is locally common across England and Wales north to the Humber, though mostly coastal in the West Country, and more local and rare to the far north of Scotland, it is present on all the English islands and has been recorded from the Outer Hebrides but appears to be absent from Orkney and Shetland. Adults occur in a wide range of terrestrial habitats including all types of grassland from damp humid pasture and permanently shaded marginal vegetation to dry calcareous hillsides exposed to the sun, they also occur on wetland margins and may be abundant on arable land during the summer. They are present year-round, peaking in the spring and autumn, and may be found among low-growing plants, under stones, in litter and moss or under fallen vegetation, during the winter mostly in the soil under debris but occasionally in tussocks and in the spring they may be active on the surface, and although not myrmecophilous they are often found near ant nests as they predate ant larvae and pupae, they are otherwise known to feed on a range of small invertebrates and are considered beneficial among crops because while they do not climb stems they are known to predate large numbers of terrestrial aphids. New generation adults occur from mid-summer and these are usually active for a while before overwintering, they may also be active during mild winter spells but mating occurs in the spring and larvae develop through the spring and summer. Adults are easily found by searching under debris and plant remains but they often appear when sieving compost and are frequent in extraction and pitfall samples.
Adults are easily identified by the size, the form of the pronotum and the colouration. 4-5mm. Body finely and densely punctured and pubescent, rather shiny dark red with the head and abdomen from the third tergite variously darker, often black, legs yellow, palps yellow, antennae yellow and darkened from the third or fourth segment. Head quadrate, produced and narrowed in front of weakly convex eyes, temples rounded to a distinct neck and vertex
flat, anteriorly with a V-shaped ridge between the antennal insertions. Maxillary palpi long and thin with a reduced and pointed apical segment, this is suggestive of Paederinae but here the antennae are inserted laterally rather than on the dorsal surface. Antennae 11-segmented and filiform, the segments becoming progressively shorter and slightly wider towards the apex. Pronotum quadrate and broadest in front of the middle, lateral margin almost straight in the basal half, apical half smoothly rounded to the anterior margin, posterior angles distinct and basal margin straight and very finely bordered. The pronotal disc is flat with a sharply defined longitudinal impression and this is the best guide to the species. Elytra short and transverse with sloping shoulders and widely sinuate apical margins, the posterior angles perpendicular. Abdomen widest behind the middle, with very fine and sparse punctures and pubescence and strongly raised lateral margins, each tergite with a sinuate line across the base which is directed backwards towards the lateral margins. Legs slender and very long, the tarsi about as long as the corresponding tibia. Tarsal formula 4,5,5.