Hermaeophaga mercurialis (Fabricius, 1792)
A widespread Western Palaearctic species with a mainly central and south-eastern European distribution, extending into Asia Minor, Ukraine and western Russia and north to the UK and southern parts of Sweden, it occurs in the south of France and south to central Italy but is absent from Spain and Portugal, here it is locally common in South Wales and England below the Wash and there are a few scattered records further north to Cumbria. Typical habitats include woodland, hedgerows, heathland and grassland, often in shaded situations and often on light chalky soils, where the host, dog’s mercury (Mercurialis perennis L.) is abundant. Here the species is monophagous but in central and Southern Europe Mercurialis ovate Sternb. & Hoppe is also used. Adults occur year round; they overwinter in tussocks, among litter or under bark etc. and become active early in the year, they peak in abundance during May and June and remain active until late into the autumn, through the late spring and summer they usually occur in large numbers and may be detected by the numerous small holes produced as they consume the host foliage. Mating occurs early in the season and oviposition continues through April, May and June. Eggs are laid in the soil at the base of host plants and larvae emerge about ten days later, they bore into the roots to feed but may also feed on leaves near the soil, they pass through three instars and are fully grown within four weeks. Mature larvae enter the soil and construct a cell in which they pupate, the pupal stage lasts about two weeks and new-generation adults occur from August although it is thought that a proportion of third-instar larvae and pupae overwinter to produce adults from February which remain in their pupal cells until the spring. So far as is known adults have only vestigial wings and are incapable of flight but they have been recorded in numbers in flight-interception traps from April until July. Sampling is straightforward; they may be obtained in numbers by sweeping host material through the season or by sampling nearby tussocks or leaf-litter etc, they generally occur on light chalky soil but will also be found in permanently damp or wet woodland situations on heavy clay substrates.
A small, convex-oval species readily identified by association with the host plant. 2.3-4.0mm Body entirely dark blue but for parts of antennomeres 1-4 and legs variously reddish-brown. Head transverse with prominent eyes, in life usually mostly concealed beneath the anterior pronotal margin, antennae 11-segmented and inserted in front of the eyes, the insertions separated by about the length of the basal segment. Pronotum widely transverse, evenly curved laterally from sharp posterior angles to a curved anterior margin, basal margin sinuate and very finely bordered, surface smoothly convex and very finely punctured, with a short longitudinal impression either side in front of the base, these joined by a variously-developed transverse impression. Elytra oval with sloping shoulders and separately rounded apical margins, surface finely and randomly punctured and often appearing faintly rugose. Hind femora broadly developed compared with the middle femora, tibiae smooth, without external teeth or angles, each with a small apical spur, tarsi pseudotetramerous. Basal segment of male front tarsi dilated. Claws with a distinct tooth towards the base.