Sphaeroderma
Sphaeroderma is a small Chrysomelid genus containing only two species in Britain and mainland Europe. The antennae are placed close together on the forehead (Galerucinae). The hind femora are enlarged for hopping (Alticini). The pronotum has no grooves or fovea which separates it from the only other 'red' genus (Neocrepidodera) with which it may be confused in the field, Neocrepidodera having a well defined basal groove and two equally visible lateral notches or elongate fovea. The genus keys out quite comfortably in Joy. Care should be taken if using Fowler as fowler's testaceum (non Fab.) is, in fact, rubidium (Graells) and his cardui (Gyll) is testaceum (Fab.) Joy separates the two species on elytral shape; 'quadrate' in S.rubidum and 'slightly elongate' in S.testaceum, and length; S.rubidum being smaller (2.3-3.5mm) and S.testaceum larger (3.5-4mm). Bienkowski, however, also uses two other diagnostic characters; Anterior corners of pronotum prominent in S.testaceum, not prominent in S.rubidum and pronotum with coarse punctures basally in S.testaceum, S.rubidum finely punctured throughout. The pronotal pictures below do not clearly show the anterior corners but the difference in puncturation is obvious.
S.rubidum	S.testaceum
S.rubidum	S.testaceum