Sphaeroderma rubidum (Graëlls, 1858)
This is a generally common species throughout Europe although sporadic in some northern areas, extendling to the UK and southern provinces of Fennoscandia, east to western Russia, Caucasus and Ukraine and widespread across North Africa from Morocco to Lebanon. Here it is common throughout England and Wales including the islands, and much more local and scarce in Ireland and southern Scotland. Host plants include a range of Asteraceae, especially various thistles (species of Cirsium Mill, Carduus L. and Onopordum Viall) but also saw-wort (Serratula tinctoria L.), safflowers (Carthamus tinctorium L.), burdocks (Arctium spp.) globe artichoke (Cynara cardunculus L.) and cornflowers (Centaurea spp.), adults feed on foliage causing numerous small holes but they also visit flowers and may occasionally be found on foliage of broadleaf trees and shrubs. Typical habitats include anywhere the hosts are common, roadsides, heaths and moors, grassland and arable land, parks and gardens etc, and they are often common on disturbed ground. Adults occur year-round but very few individuals overwinter and only small numbers occur in early spring, they become common from late May or June when the new-generation appears, they remain so until September and persist into the autumn. Mating occurs from late May or June and continues over several months and oviposition occurs from July until October. Eggs are laid singly on the underside of leaves, usually near to a large vein and often towards the middle of the leaf, and larvae emerge within two weeks, upon leaving the egg they immediately bore into the tissue beside the vein and begin to mine, at first the mine is full depth across the leaf and often meanders or forms loops, these early mines contain little frass and have irregular margins but as the larva grows the mines become much wider and more regular, last (third) instar larvae are very broad and completely fill the mine. Larval development takes about a month; fully grown larvae occur from late August into and the majority of these will leave the leaf and enter the soil to form a cell a few centimetres below the surface, these will overwinter and pupate from April to July. The pupal stage lasts between four and six weeks and so new-generation adults appear over a long season, they begin feeding soon after eclosion but most will aestivate through the summer and there is only a single generation each year. Sampling is usually by sweeping suitable vegetation from spring until the autumn and adults will only rarely occur in winter tussock or moss samples.
Sphaeroderma rubidum 1
Sphaeroderma rubidum 2
2.3-3.5mm. Very convex and only slightly elongate, sometimes appearing almost circular in outline, and entirely pale brown when mature. Head transverse with large convex eyes, usually substantially hidden under the pronotum, vertex flattened and finely punctured, antennae inserted anteriorly beside the inner margin of the eyes, the separation slightly less than the basal segment. Antennae 11-segmented with all segments elongate. Pronotum broadest at acute posterior angles and strongly narrowed to a rounded (from above) anterior margin, surface very finely punctured or impunctate in places and lacking any basal grooves or fovea. Elytra quadrate to slightly elongate with sloping shoulders, strongly rounded lateral margins and continuously curved apical margin, surface randomly and finely punctured, without impressions or fovea. Legs long and robust, the hind femora greatly expanded compared with the middle femora, tibiae slightly curved and gradually broadened to obliquely-truncate apical margins. All tibiae slightly expanded at the outer apical angle and bearing a small spur. Tarsi pseudotetramerous with the third segment strongly bilobed, basal segment of all tarsi dilated in the male.