Rhizophagus picipes (Olivier, 1790)
POLYPHAGA Emery, 1886
CUCUJOIDEA Latreille, 1802
RHIZOPHAGINAE Redtenbacher, 1845
Widespread in central and northern Europe; absent in many Mediterranean regions but extending north into the UK and the Baltic countries where it reaches into southern provinces of Norway and Sweden, to the east it extends sporadically into European Russia. The species is very local and generally scarce throughout this range, although it is probably more common in cooler northern regions. In the UK it is very local and scarce in Southern and Central England and Wales; it was formerly more widespread, extending into Southern Scotland, but it is thought to have declined over recent decades. Associated with a range of broadleaf trees, especially alders (Alnus Mill.) and poplars (Populus L.), and much less frequently with conifers, especially pines, and usually in damp or wet situations such as river or lake margins or carr. Adults also occasionally occur among plant debris, compost and decaying sporocarps. Adults are present year-round; they overwinter under bark or among moss or litter near to suitable trees, and are active from March until September or October, peaking in abundance during May and June, and again in September. They are nocturnal and they fly on warm evenings to visit sap and insect-infested wood where the larvae are thought to develop in beetle galleries etc. It is likely that both adults and larvae are detritivores or mould feeders, but adults have been recorded from a range of beetle galleries including those made by larvae of Elateroides dermestoides, and the bark beetles, Xyleborus dispar (Fabricius, 1792) and Taphrorychus bicolor (Herbst, 1794), suggesting that either or both may also be predatory. Although very local and rare the species is sometimes abundant where it occurs. Adults may be found under damp or even wet bark or at sap during spring and early summer, otherwise they may occur in suitable extraction samples or among flood-refuse.
2.5-4.0 mm. Elongate and parallel-sided, body very dark grey or (usually) black, appendages and sometimes the abdominal sternites brown. Head large and transverse, broadest across small and protruding eyes and with long and converging cheeks and temples, frons shallowly and obliquely depressed, vertex finely punctured throughout. Antennae inserted laterally, near the outer margin of the mandibles, 11-segmented with a two-segmented club (both segments visible), segment 3 elongate; about as long as segments 4-6 and much longer than the second segment. Pronotum quadrate or slightly transverse, lateral margin weakly curved to rounded angles, surface evenly convex, without structure, moderately strongly but not densely punctured, often more sparsely so towards the lateral margins. Elytra narrowing behind the middle to a continuous apical margin, shoulders rounded and slightly projecting forward, striae parallel and regularly punctured from the base and fading in the apical third where the cuticle is often rugose, interstices smooth, at most with only scattered fine punctures. Legs short and slender. Femora unarmed. Tibiae broadened from the base to truncate apices; middle tibiae (at least) with fine but usually obvious spines on the outer margin. Apical abdominal sternite in males with a pair of longitudinal setiferous calli; in females with a single small median protuberance.