Cassida vibex Linnaeus, 1761
This generally common species occurs from lowland to low mountain altitudes throughout the Palaearctic region from Portugal east to China and Japan and north to the UK, southern Fennoscandia and Karelia; here it is common across South Wales and England north to South Yorkshire although records from the West Country are mostly coastal. Adults occur year-round in a wide range of habitats, from fens and marshes to woodland margins and clearings, parkland, heaths, commons, gardens and coastal dunes etc, they are active from April and generally abundant from May until September, persisting into October when they enter leaf-litter to overwinter although they may become active in mild spells through the winter. Host plants include various thistles, Cirsium and Carduus spp. and other Asteraceae e.g. knapweeds, Centaurea spp, burdock, Arctium lappa L. and saw-wort, Serratula tinctoria L. although during the spring and summer adults may by swept from vegetation generally. Oviposition occurs in late spring and early summer; eggs are laid singly or in small batches on the underside of host leaves and mat be left exposed or disguised with frass. Larvae emerge after a week or so and begin feeding on the upper surface of leaves, at first exposed but they soon disguise themselves by accumulating masses of faeces on the dorsal surface, they develop rapidly and are fully-grown within four or five weeks. Pupation occurs on the surface of foliage, usually where a leaf is partly folded along a vein, the pupa lies within the moulted larval skin attached to the leaf by strands of silk, and adults eclose after a week or so, the new generation appearing from late July. After C. rubiginosa this is our commonest species in the south of England and should soon be recorded from general sweeping, especially in the vicinity of thistles where the two species will often occur together, adults are fully-winged and capable of flight and so may turn up in any suitable situation.
Adults are distinctive due to the bicoloured elytra. 5.5-8.0mm. Broadly elongate-oval and continuous in outline, dorsal surface entirely bright green, in life with a metallic lustre, with the base of the pronotum and the elytral base and suture extensively dark, ventral surface entirely dark with the explanate pronotal and elytral margins green. Preserved specimens soon fade to pale yellow but retain the dark markings. Pronotum smoothly-rounded anteriorly and with rounded perpendicular posterior angles, surface densely punctured, usually narrowly darkened along the basal margin. Elytra moderately steep laterally and with wide explanate margins, each with two rows of punctures between the third and fifth interstices and other variously defined rows of punctures near the base but often mostly randomly punctured, colour as above but also commonly with a small dark spot on the declivity just behind the middle, surface with fine and very short pubescence that becomes visible with strong oblique lighting. Antennae pale towards the base, otherwise extensively darkened. Coxae, trochanters and basal half (at least) of the femora dark, apical half of femora, tibiae and tarsi pale. Three basal segments of each tarsus broadly expanded, the fourth tiny and the fifth long but within the lobes of the third, Claws simple, smooth to the base.