|Rhagonycha elongata (Fallen, 1807) Notable A|
Specimen kindly loaned by Dr. Martin Luff
|So far as we are aware this small and dark soldier beetle does not occur
anywhere near our Watford area , and nor does it seem likely to. There are verified modern (post 1979) records
from the Scottish highlands south to the Grampians, and from Orkney
(Alexander, 2003). Adults occur in boreal
woodlands from May to July. (Alexander)
6-7.5mm. Head entirely black, surface dull due to microsculpture, vertex weakly concave between strongly convex and protruding eyes. With very fine pale pubescence, most obvious behind eyes and along temples. Antennae and palpi dark, paler towards base. Terminal segment of maxillary palps dilated. Pronotum transverse (L22 : W29). Dark pitchy red, surface shiny, more so than head, very finely punctured and with pale pubescence. Microsculpture just visible at X20, most obvious anteriorly. Broadest in front of obtuse hind angles, lateral and basal margin raised, front angles smoothly rounded, surface without fovea. Elytra black or very dark pitchy, surface shiny, transversely rugose and finely punctured, pubescence pale and recumbent. Each elytra with three longitudinally raised lines on dorsal surface and a fourth starting on reflexed surface under humerus and joining lateral margin behind middle. Femora dark, lighter towards apex. Tibiae dark orange-brown, darker towards apex. Tarsi dark, segment three not bilobed. All claws divided longitudinally
Description taken from 1 specimen. Golspie, Sutherland June 1962. (Kindly loaned by Dr Martin Luff.)
Fowler (1887) quoted the species as local, as did Joy (scot;L). In Hyman and Parsons it is classed as Scarce A. Through lack of opportunity to examine Voucher material Alexander does not include records from south of the Forth-Clyde line and ponts out that Cantharis paludosa and the dark form of Cantharis nigra are superficially similar. (the differences between these two genera are given in our family description) And of course this kind of empirical approach must be applied to older records but we must be very aware of this when looking at eg the NBN presentation, here there are records from around the lake district (old and recent), Anglesey (post 1950), the north Norfolk coast (post 1990) and a single record from the midlands (pre 1949).
It seems likely that most workers (and certainly most amateurs) will have used Joy to identify this species and, using his key to Rhagonycha, this is probably safe in all cases ie
4(1) Head black.
6(5) Thorax entirely, or in part, black, Elytra entirely black or yellow.
7(10) Thorax entirely black; L 6-7.5mm
8(9) Elytra, antennae and femora black, or nearly so.....elongata
9(8) Elytra, antennae, except apical joint, and legs yellow....lignosa
and so the mistake must be made at the generic stage where separation is based purely on the middle and hind third tarsal segment; bilobed in Cantharis and simple in Rhagonycha. Without experience or reference material this may be subjective as the third segment is narrow at the base and broadened towards the apex in Rhagonycha, but not bilobed. In the Cantharis key R.elongata will go awkwardly to C.paludosa (Which, at 4-5mm, is too small) or through couplet 22(21) ('El. entirely black, femora entirely yellow, or with apex narrowly black, or base obscurely darker') to fulvicollis F.(C.nigra DG).
Care needs to be taken assigning the correct genus; the form of the claws must be examined (although the third tarsal segment is very obvious with experience) and, once correctly assigned to Rhagonycha, the specific identification should be straightforward.
A melanic form of R.limbata TH. is known (Fitton) but the black pronotal pattern is obvious against the darkened margins.
The point of this discussion being that either the species has been more widespread and has occupied different habitats in the past or it has been misidentified on several occasions. Reliable identification in the future would be useful.
See ID Aids for a key to the family