A pair of species which myself and others have had trouble with. It may not be the toughest ID challenge amongst the British Carabidae but if people find this detailed treatment helpful, I will write up others.
|Overall colour||Dirty straw and blackish.||Reddish-brown and blackish.|
|Pronotum||Less transverse (width a little greater than length), more concave at sides and with better-marked hind-angles. Usually darkened in the middle with contrastingly paler hind-corners.||More transverse (width > length), at most a barely perceptible concavity before the less well-marked hind-angles. Usually more uniformly coloured, less contrasting.|
|Head and eyes||Narrower, with smaller eyes and less of an angle between the temples and the neck.||Broader, more triangular head, with larger, more convex eyes, and a more obvious angle between temples and neck.|
|Scutellum and elytra||Scutellum dark, clearly darker than shoulders of elytra. Dark markings of elytra extend forward narrowly along suture, reaching and surrounding the scutellum.
Dark markings tend to extend right to the tips of the elytra and all the way to the side margin.
Elytra more elongate and with straighter sides.
|Scutellum pale, concolourous with shoulders of elytra. Dark markings of elytra extend forward narrowly along suture but do not reach the tip of the scutellum.
Dark markings tend to stop short of the tips of the elytra and also to leave a narrow pale side-margin.
Elytra less elongate and with more rounded sides.
|Palps (maxillary and labial)||Less swollen (perhaps more so on males); tapered to a point though not especially sharp at the extreme apex. Largest (terminal) segment slightly infuscated in middle.||More swollen (especially males); (slightly obliquely) truncate at the tip of the terminal segment, on both maxillary and labial palps (more obvious on male). Palps of uniform reddish colour throughout.|
|Abdomen||“Entirely piceous black” (Lindroth, 1974).||“Infuscated but brown or pitchy rather than black” (Lindroth, 1974).|
|Penis||Stouter; internal sac with two rod-like sclerites; see illustration in Lindroth (1974).||Much more slender; internal sac without defined sclerites; see illustration in Lindroth (1974).|
|Wings||Full-winged individuals are rare.||Probably always short-winged.|
|Range in Britain||Largely coastal, throughout Britain.||Coastal: southern counties and Thames estuary.|
Originally written in 2004 but now updated after reference to 60 specimens of notatus and 47 of vectensis, and with the addition of photos taken using the excellent equipment at the Hope Department of Entomology, Oxford University Museum of Natural History (thanks to Darren Mann and James Hogan). Comments welcome!
Lindroth, C.H. (1974) Coleoptera, Carabidae. Handbooks for the identification of British insects, vol. 4, part 2. London: Royal Entomological Society.