Aleochara curtula (Goeze, 1777)
POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
ALEOCHARINAE Fleming, 1821
ALEOCHARINI Fleming, 1821
Aleochara Gravenhorst, 1802
This generally common species occurs from lowland to alpine altitudes throughout Europe with the exception of the most northern provinces of Fennoscandia, further afield it is among the most widespread members of the genus, occurring across the Palaearctic region east to Japan and south into the Oriental region and tropical Africa, it has also become established in north America since the early twentieth century and has been widely recorded in South America. Here it occurs throughout the British Isles; it is locally common throughout south and central England and rather more local and scarce in the West Country and further north to the Scottish Highlands and Outer Hebrides. Adults occur year-round and are active from early spring until the autumn, they are typically attracted to freshly decaying carrion but may also be found at dung or strongly smelling decaying vegetation e.g. we found them in numbers among foul-smelling decaying seaweed in North Somerset and they may be abundant in decaying terrestrial fungi in the autumn, but through the spring and summer they will quickly be attracted in numbers to carrion. They run quickly about the host material predating insect larvae etc. and when disturbed will either take flight or vanish into adjacent vegetation or crevices in the ground so that to sample them the best way is to sieve a sample or throw it onto a tray. Mating occurs throughout the season and eggs are laid into the host material. Larval are solitary parasites of cyclorrhaphous diptera, they develop rapidly and pass through two distinct stages; first instars are campodeiform and very active, they search through host material until they find a suitable dipteran pupa, here they are guided by volatiles from the pupal spiracles, they then chew their way into the pupa and feed on the contents, the following two instars are eruciform and will continue feeding in situ until they pupate. Each pupa will host only a single larva and so competition is intense among late arriving larvae and after a certain time the host material becomes unattractive to adult beetles, because of this there is also a wide variation in adult size as pupae of various sizes and of several host species can be utilized. Adults may be obtained in numbers using carrion-baited traps, freshly-decaying fish placed among leaf litter in just about any situation will usually attract many specimens, on a warm day they may even be seen flying in and vanishing beneath the sample, in warm weather they will also appear occasionally when sweeping among vegetation or above dung pasture.
This large and broad rove beetle is distinctive due to the bicoloured elytra, broadly transverse antennal segments and smoothly convex mesosternum. 5-9mm although smaller specimens very occasionally occur, head, pronotum and abdomen entirely shiny black, elytra substantially dark reddish-brown with the base and lateral margins variously darkened. Legs entirely pale, antennae dark brown or black with the basal segments paler. Entire dorsal surface with moderately dense pale pubescence. Head circular and smoothly convex with large and slightly protruding eyes that occupy about half the lateral margin, vertex and clypeus finely and moderately densely punctured. Antennae a little shorter than the head and pronotum combined, inserted in front of the eyes, the insertions visible from above, segments 1-3 elongate, 4-10 transverse, the distal segments very strongly so, at least 2.5:1. Penultimate maxillary palpomere broadened to a truncate apex, terminal segment very small and narrow. Pronotum transverse and broadest before the base, laterally curved and narrowed from rounded posterior angles to a continuously-rounded apical margin, all margins very finely bordered, surface smoothly convex and punctured about as strongly and a little more densely than the head. Mesosternum without a raised median longitudinal ridge. Elytra transverse and shorter than the pronotum, broadest about the middle and slightly narrowed to sloping shoulders and rounded posterior angles, basal margin widely sinuate and sutural margin finely raised, surface more densely punctured than the forebody. Abdomen with strongly raised lateral borders, all tergites moderately densely punctured, the first two with a raised border across the base that curves obliquely back towards the lateral margins. Eighth tergite sexually dimorphic; smoothly rounded in the female and emarginate in the male. The aedeagus is unique among our species in having an apical ‘hook’.
The only UK species likely to be confused with curtula is A. discipennis Mulsant & Rey, 1853, a rare dung frequenting species of similar size and colour, but here the distal antennomeres are not so strongly transverse, the mesosternum is raised into a fine longitudinal ridge and the aedeagus lacks an apical hook.