Stenagostus rhombeus (Olivier, 1790)
A very local insect of old, naturally preserved woodland and orchards across south and east England, with a few scattered records in the Midlands and south Wales. Absent from the West Country (Mendel). Adults are crepuscular or nocturnal and strong fliers, being attracted to light. By day they rest under bark or among leaf litter; several specimens were found beneath damaged alder bark during 2009 at Cowley (Middx). larvae inhabit decaying wood in stumps and decomposing dead stems of both deciduous and coniferous trees, being partly saprophagous. Pupation occurs in the spring mostly in the harder layers of wood and often in the tunnels of Cerambycidae. Adults are occasionally attracted to M.V. in Whippendell wood during July. Bionomics are described by Schimmel (1982).

16-18mm. Antennae light brown, inserted beneath anterior clypeal angles, segment 1 a little shorter than the distance between insertions, segment 2 very small and only slightly elongate. Serrate in both sexes and with a raised ridge along the centre of segments 5-11; terminal segment constricted and elongate in anterior third, so appearing 12 segmented.
Head, thorax and elytra punctate and pubescent throughout. Pronotum light brown, elongate with front margin bisinuate, front angles produced. Sides sinuate and hind margin almost straight medially; strongly sinuate either side and with a small longitudinal incision either side just before hind angles. Hind angles strongly produced and with a small ridge parallel to the lateral margin. Elytra often darker, contrasting with head and thorax, with well impressed striae and finely and densely punctured interstices. Pubescence behind middle forming oblique transverse patterns, to the naked eye this appears as a dark rhombus among the lighter pubescence. Side margin weakly explanate towards apex. Legs light brown tarsal segments 1 and 5 elongate, 2 and 3 lobed below.

Description from 3 Watford specimens at X20


Schimmel, R. 1982: Zur Kenntnis der Biologie von Stenagostus villosus. Mitt. Int. Entomol. ver. Frankfurt a. M.7:8-14