Orchestes Illiger, 1798
Includes about 140 species of tiny ‘flea weevils’, the distribution is mainly Holarctic although species are also known from Tropical Africa and Western Australia, they are by far most diverse in eastern Palaearctic regions, notably Japan, and the total number of species may greatly increase as there are many from Borneo and adjacent regions that very probably belong here but remain incertae sedis. The European fauna includes eighteen species, and by contrast seven species are known from North America, of which two are established introductions from Europe. There have been the usual nomenclatural changes; many species were formerly classified within the genus Rhynchaenus, and various subgenera such as Salius Schrank, 1798, Euthoron Thomson, C.G., 1859 or Threcticus Thomson, 1865 will be found in older works and on various websites, and so an up to date checklist covering the tribe should always be used when naming specimens. As currently accepted our UK fauna includes nine species classified in two subgenera (see below).
Typical habitats are open woodland and wooded heaths and pasture etc. and adults tend to be common where they occur; the generally abundant O. fagi is likely to be the first encountered and this may be found in very large numbers when working beech. They are thought to be univoltine, at least in the UK, with adults overwintering and usually active over a long season, the over-wintered and summer generations overlapping but not breeding. Reproduction occurs in spring and summer and larvae mine host foliage, usually dropping falling to the ground when fully-grown and pupating in a subterranean cell.
Generally referred to as ‘flea weevils’ due to their ability to jump powerfully when disturbed. They are small, at most 4.5 mm but usually much smaller, broadly elongate and discontinuous in outline; many are drab brown or grey but several have striking patterns which may be useful field characters. Head with large eyes that form the outline from short temples to the base of the rostrum, interocular distance small, narrower than the rostral width, surface closely punctured and with elongate scales which usually leave the cuticle visible. Rostrum weakly curved but strongly down-curved so that in life it lies beneath the head, moderately long, usually slightly thickened from the base and widened about the antennal insertions, scrobes only narrowly visible from above. Males of some species have a longer rostrum when compared with females. Antennae inserted about the middle of the rostrum, in males usually inserted further from the base, 11-segmented with the basal segment (scape) longer than the second segment which is inserted at an angle (geniculate), funiculus 6-segmented. Pronotum transverse and rounded laterally, widest about the middle or towards the base, surface usually strongly and densely punctured and with elongate scales throughout, lateral margins with or without long outstanding setae. Elytra elongate with rounded shoulders and a continuous apical margin, usually with strongly-punctured striae and roughly-sculptured interstices, vestiture varies but usually with elongate scales which may or may not form a pattern. In many species the elytral margins, especially about the shoulders, have long outstanding setae. Hind femora greatly developed and in most (the only UK exception being O. rusci) with a series of tubercles or teeth along the ventral margin, front and middle femora normally developed and without ventral teeth. Tibiae narrow and usually straight or almost so, hardly broadened from the base, apex simple and with tiny apical spurs. Tarsi pseudotetramerous with the third segment widely bilobed and the fourth segment diminutive. Claws free and distinctly toothed at the base. Among our UK genera Orchestes may be distinguished by the form of the antennae; geniculate with the scape distinctly longer than the second segment and the enlarged hind femora. Pseudorchestes pratensis (Germar, 1821) (formerly included within the present genus) is broadly similar and might be mistaken for O. fagi, but here the first two antennal segments are about equal in length. Members of Tachyerges Schönherr, 1825 are also very similar, and this genus also includes strikingly-patterned species, but here the antennal funiculus is always 7-segmented.
Subgenus Alyctus Thomson, C.G., 1859
Subgenus Orchestes Illiger, 1798