Ptilinus pectinicornis (Linnaeus, 1758)
This is the type species of the genus Ptilinus Muller, O.F., 1764, a small group of 9 Nearctic and 5 Palaearctic species. All are small beetles, 3-6mm and drab coloured brown or grey, elongate and convex, characterized by the pro-tibiae being produced into a triangular spine and the greatly enlarged, pectinate antennae in the male. Species from the Neotropical region formerly included are now classified into other genera. All species are saproxylic, developing in dry wood.
A widespread Palaearctic and Northern Asian species, the distribution extending east to, but not including, China. Following introductions there are also records from Australia and the U.S.A. but in neither region has it become widespread. It is the only species to occur in the U.K. where it is widespread and locally common throughout England and Wales and more scattered and rarer further north. The species is xylophagous, developing in a wide range of broadleaf trees e.g. oak, elm and ash etc. but especially in beech and willows. They occur in just about any habitat with suitable host trees; gardens, open or dense woodland, parkland etc. but overgrown and dense woodland situations often host large populations. Adults are active by day when they may be seen running on the surface of trunks and logs, and more especially so on areas devoid of bark, in this situation in hot weather they are usually accompanied by a swarm of adults, mostly males, flying between 3-5m above the wood. They mate in the spring, and during the afternoon and evening the females may be seen boring into wood in order to construct a brood chamber where she will lay her eggs and remain to protect them and the early stage larvae. Where an infestation occurs there is generally a wide area of quite closely packed holes, 1-2mm wide on exposed and dead xylem, these are filled with very fine wood powder which will solidify over time. Development usually takes a year, and during the following spring new holes will appear along with characteristic lines of fine wood dust produced as the new adults chew their way out of the wood. The adults are generally common until June or July and
will often come to u.v. light. There are records of adults, or even infestations, occurring indoors and it is thought that these originate in timber yards where dry, processed wood is stored. The clerid, Tillus elongatus (Linnaeus, 1758), is a specialist predator of Ptilinus and the two species are often found together; the clerid will be found active both by day and at night where large colonies occur.
So far as the U.K. fauna is concerned this small beetle, 3.5-5.5mm long, is distinctive, it is superficially similar to some other members of the family but the antennae are unique; very strongly pectinate in the male, and very broadly serrate in the female. The overall colour is brown with the elytra and appendages usually lighter. The entire dorsal surface has very fine, short pubescence. Head deflexed and mostly hidden from above, densely and coarsely granulate and with convex and protruding eyes which are larger in the male. Pronotum convex, rounded laterally and with obtuse front angles, the cuticle shiny with dense tubercles anteriorly. Scutellum large and triangular. The elytra are parallel-sided and completely cover the abdomen, randomly punctured, and each with 3 or 4 narrow longitudinal unpunctured areas. The legs are short, with all tibiae bearing an outward facing triangular spur at the apex, otherwise smooth. Tarsi 5-5-5; 2 basal segments elongate, 3 and 4 transverse and lobed, 5 elongate and expanded towards the apex.