Pilemostoma fastuosum (Schaller, 1783)
This widespread western Palaearctic species occurs from Spain eastward to Siberia and Mongolia, in Europe it is locally common in southern and central areas but further north, where it extends to Denmark and the south of Sweden, it is generally very local and rare, in the UK it occurs sporadically in the south of England and South Wales and is thought to be in decline although it has always been scarce and very local. Adults occur year-round, they become active early in the year and peak in abundance in May and June, they prefer open situations such as grassland and wooded margins, especially in calcareous regions and often occur on hillsides exposed to the sun but they might also be found in wetlands and disturbed wasteland and road verges. Host plants include ragwort, Senecio jacobaea L, ploughman’s spikenard, Inula conyza DC, 1836 and fleabane, Pulicaria dysentrica (L.) and adults have also been found on mint. Adults feed on foliage during early spring, causing small round holes in the leaves, before mating begins in April. Oviposition proceeds through May and June when small batches of two or three eggs are laid on the underside of host leaves and covered with a translucent brown secretion, larvae emerge within a week or two and develop rapidly, remaining underneath the leaves and consuming the lower layers, they pass through four instars and pupate beneath the leaves. Adults eclose soon afterwards and the entire cycle from egg to adult takes about six weeks. Freshly emerged adults are pale yellowish or greenish and will often remain inactive for a few days before the colour develops and they begin feeding, they remain active until the autumn when they will enter leaf-litter or moss to overwinter, unlike many tortoise beetles they are short-winged and cannot fly.
The striking dorsal colouration will readily distinguish this species among our fauna, only Cassida murraea has a similar red colour but here there are no dark markings to the pronotum. More generally it is distinguished from all species of Cassida by having antennal grooves towards the lateral prosternal margins but this should never need to be examined. 4.2-6.2mm. Pronotum and elytra finely microsculptured bright red with extensive black markings; on the pronotal disc and towards the lateral margins as well as a discrete smaller spot near the anterior edge, on the elytra a longitudinal and heavily indented, sometimes fragmented, dark mark on the disc and the suture extensively dark, these are very variable. Appendages dark, base of antennae red. Pronotum evenly rounded from near-perpendicular posterior angles, basal margin strongly bisinuate, disc finely punctured, wide explanate margins strongly punctured, especially towards the base. Elytra only slightly wider than the pronotum at the base, basal margin strongly sinuate and dentate, striae regular and quite strongly punctured to the apical third or quarter where they fade, explanate margins strongly punctured. Margins of pronotum and elytra distinctly bordered. Claws strongly curved and toothed at the base. Teneral specimens are pale pink or yellow, often with a glossy metallic lustre, and these may be observed active on vegetation early in the season, the dark markings are always well-developed and should make the identity obvious. On the continent mature specimens are known to retain this pale yellow or green colouration.