Masoreus wetterhallii (Gyllenhal, 1813)

Masoreus wetterhallii is a generally scarce and local, mostly coastal species in the UK, occurring from South Wales to Lincolnshire and also inland on the Brecklands of East Anglia. Typical habitats are among low vegetation on dry sandy or gravelly soils or at the base of plants on dunes and dune slacks, which is much the same as in Europe but here it also occurs on open grassland on suitable soils and is often associated with heather and other low-growing plants on sandy heathland. Adults occur year-round, they are diurnal but rarely found away from plant roots and rosettes etc, and reproduction occurs in late summer and autumn.  Larvae are active in the autumn before overwintering in the soil and completing their development in the spring. New generation adults occur from early summer and it would seem that dispersion occurs by walking as macropterous individuals are rare and flight muscles tend to be undeveloped. Adults usually occur in small numbers and often among larger populations of other carabids that frequent similar habitats; on the continent often with Calathus ambiguus (Paykull, 1790), Harpalus anxius (Duftschmid, 1812), Syntomus foveolatus (Geoffroy in Fourcroy, 1785) and Cymindis macularis Mannerheim, 1824.

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4.5-6.0mm. Superficially similar to various Trechinae but lacking any deep furrows on the head and with fully-developed maxillary palps, this species is readily distinguished by the truncate elytra and series of short spines along the outer margin towards the apex of the fore tibiae. Body entirely brown, usually with the head and apical half or two-thirds of the elytra darker, appendages entirely pale brown. Head with large convex eyes and short converging temples, vertex and frons smoothly convex and very finely wrinkled and punctured, inner margin of eyes with a single setiferous puncture, and the antennae pubescent from the fourth segment. Pronotum widely transverse, broadest slightly in front of the middle and smoothly curved to rounded anterior and posterior angles, basal margin slightly sinuate laterally and produced medially. Elytra broad and almost parallel-sided, with rounded shoulders and obliquely-truncate apical margins which almost cover the abdomen, striae, including a short scutellary striole, weakly impressed and almost impunctate, interstices weakly convex and very finely rugose and punctured; the third with 2 setiferous punctures adjacent to the third stria. Basal pro-tarsomeres dilated in the male.