Hister unicolor (Linnaeus, 1758)

Right Tibia
Widely distributed throughout the British Isles (Chinnery,2005) although less frequent in the north (Fowler), it is generally quoted as local (Halstead, Joy) but may be common where found. They occur year round in dung and are easily found by disturbing this medium, when disturbed they remain stationary with the appendages held tightly into the body and so, until some experience is gained in looking for these, a little care is needed. In any case they often turn up in dung extractions. Both cattle and horse dung will host this species which is usually present singly or in pairs and often among larger numbers of Magarinotus spp. They also occur in other habitats although in our experience not so frequently as dung; among rotten organic matter, at sap (Harde) and carrion (Fowler). We have found them in heaps of warm composted grass cuttings, from beneath a decomposing rat and in some numbers among the well rotten, slimy and ammoniacal remains of terrestrial bracket fungi beneath Fagus in Cassiobury park. They are common on dung pasture throughout our area and on hot, sunny days may be netted in flight. Adults are active nocturnally and come to light, both adults and larvae are predatory on other insects, especially dipterous larvae, around the host.

8-10mm. A large oval species usually appearing somewhat 'pointed' anteriorly due to the very prominent mandibles, entirely black but for funiculus and palpi red and protarsi dark brown. Upper surface, including mandibles, vary from smooth and shining to densely microgranulate and dull, generally with fine scratch-like lines which may be very dense. Smooth and shiny specimens resemble Margarinotus spp. in the field. Head transverse, eyes partly hidden under pronotum, clypeus bordered with a well impressed stria which is gently sinuate and generally weaker anteriorly, in dull specimens this is virtually absent along front margin. Antennae inserted under side of head by front margin of eyes, scape strongly curved at base, funiculus 7 segmented, first segment curved, club three segmented, compact and pubescent. Pronotum impunctate, widest at base and evenly rounded to protruding front angles. Front margin smoothly backwardly curved. With a well impressed stria close to front margin which continues parallel to lateral margin stopping short of the base, between this and the lateral margin a short stria begins within the front angles and ends around halfway to base. Elytra transverse (L15:W27) and impunctate. Striae well impressed and finely 'wrinkled' so sometimes appearing punctate; 1-3 complete although ending before base and apex, 4,5 and sutural striae present apically, 5 usually shorter and often interrupted. Humeral striae more finely impressed. Two subhumeral striae; the short outer one present at middle near margin and sometimes weak or reduced to punctures (Halstead) and a larger one inside this from before middle to apex. Elytral apices gently rounded and obtusely diverging. Meso and metatibiae dilated, with two rows of strong punctures on upper surface, two rows of strong spines on outer surface and stout apical spines internally. Protibiae with three teeth on outer edge, the apical bifid but often worn to an evenly rounded apex. Meso and metatarsi with strong spines beneath apices of segments 1-4. All claws simple.

Description from 4 Watford specimens at X20

Elytral striae arrangement distinctive for H.unicolor

1-5 Elytral striae
a Sutural Stria

a Humeral stria
b Ist Subhumeral stria
c 2nd Subhumeral stria