|Sphaeroderma rubidum (Graells, 1858)|
|Widely distributed and generally common throughout England, Wales and
southern Scotland including Anglesea and Man although records are generally more scattered in the west (NBN).
Occurs throughout the Watford area in a wide range of habitats wherever the foodplants are found; woodland,
parkland, scrub and wasteland, road verges etc and usually common although numbers vary widely from year to year,
during the wet spring and summer of 2007 and 2008 we have noticed a sharp reduction in numbers. They often occur
alongside S.testaceum (Fab.) and the relative abundance of these
also varies although in general both are abundant. Local sites where the species is sure to be found by general sweeping
are the Colne flood catchment along Radlett road and Common moor where a variety of thistle species are abundant.
Adults may be found on a range of plants including Knapweeds (Centaurea spp.), Thistles (Cirsium spp.),
Burdocks (Ardium spp.), Globe artichoke (Cynara) and also on trees. Larvae mine the leaves of Knapweed
while adults produce small holes in the leaves. Oviposition occurs in late summer and autumn and larvae overwinter in the
soil. Pupation occurs in subterranean earthen cells in the spring and new generation adults emerge from June, these survive
into the autumn and may occasionally overwinter in grass tussocks etc.
Sphaeroderma testaceum (Fab.) is closely similar and usually equally common, they share the same habitats and foodplants and so for recording purposes experience will need to be gained by taking a few specimens home for examination. With a X10 lens the pronotal puncturation soon becomes obvious.
On average a little smaller than S.testaceum, 2.3-3.1mm (Bienkowski). Form almost circular and very convex, elytral declivity steep, more so in male where it is almost vertical. Head shining and very finely punctate, puncturation just visible at X20. Eyes prominent and touching front margin of pronotum in normal setting. Frontal tubercles deeply bordered. Antennae inserted between eyes, insertions separated by about the length of the first segment, all segments elongate and terminal segment angled on outer side. Pronotum finely and evenly punctured throughout, very convex but entire side border usually visible from above. Front angles weakly produced, generally not visible when viewed directly from above. Surface continuous, without impressed lines or fovea, lateral margins sinuate and finely bordered, this border continues for a short distance onto hind margin, hind margin strongly sinuate. Elytra very convex, finely and randomly punctured although there is a tendency towards rows on the central area, puncturation finer in male. Lateral margin sinuate and bordered, with a row of punctures along inside edge of border and with a smooth, mostly impunctate, area parallel to margin. Entire upper surface glabrous (X20), a little more shiny in male but this is subtle and specimens need to be viewed together. Legs with fine golden pubescence. Hind femora enlarged for hopping, tarsi attached at apex of hind tibiae. First segment of all tarsi dilated in male, not quite so broadly as in S.testaceum; sides curved, in female narrower with sides almost straight. Fourth segment of all tarsi broadly lobed in both sexes, terminal segment elongate with two strongly curved and appendiculate claws.
Description from 3 Watford specimens at X20
See ID AIDS for a comparison of S.rubidum and S.testaceum