Ptinus fur (Linnaeus, 1758)
POLYPHAGA Emery, 1886
BOSTRICHOIDEA Latreille, 1802
PTININAE Latreille, 1802
PTININI Latreille, 1802
PTINUS Linnaeus, 1767
Native and widespread in the western Palaearctic region this species is now established across the Holarctic region, having been transported with the trade in foodstuffs etc, and has become established in many areas worldwide, most notably in Australia and New Zealand but in temperate regions generally and less often in warmer regions, it occurs commonly throughout Europe and has been recorded in the wild to the far north of Scandinavia, in the UK it is locally common across Wales and southern England and much more sporadic and rare further north to the Scottish Highlands. Adult beetles are long-lived and have been recorded throughout the year; in the wild they occur among decaying organic material in bird and mammal nests, tree hollows and beehives etc, they are thought to breed in the spring with larvae developing through the summer and new-generation adults overwintering among debris under bark or in hollows, in temperate regions they are univoltine but there may be more generations in warmer areas of the world. They are nocturnal and may be found by searching tree trunks and branches by night and they are also semi-synanthropic and regularly occur in houses and food storage facilities where they may infest a wide range of stored products. Development from egg to adult takes up to 6 months but under optimal artificial conditions, which are 70% RH with a good food source at 23°C, this may be reduced and the species may be continuously brooded. Adults mate among the food source and females lay small numbers of eggs into crevices among the commodity, in the wild this may be old feathers or nest material but inside it is usually the stored food or it packaging. Larvae quickly emerge and burrow into the food, they are scarabaeiform with fully developed legs and they feed internally, they usually moult three times but there may be extra instars in response to cold conditions, initially they are able to move around their host material but become immobile as they grow, they pupate in a cell within the food and adults usually eclose after a week or two. The species is cold tolerant
at all developmental stages and at least some larvae are able to enter a prolonged diapause, up to 220 days has been recorded, in response to low temperatures, and adults, which usually remain in the cocoon for a month or two in a pre-emergence period, may extend this in response to environmental conditions. Both adults and larvae feed on both animal and plant material and a wide range of stored products are attacked including herbs, spices, seeds, grains and stored foods generally, they may also attack animal skins and dried museum specimens, and this adaptability, along with the tendency of wild specimens to enter buildings and warehouses etc, makes them a persistent pest throughout their range although large numbers of adults or infestations of larvae are rare due to the low fecundity and relatively long life-cycle. Adults may be sampled by searching trunks and branches at night but they are quite likely to occur on walls inside during the summer, and they often occur in bathrooms or other areas of sporadic high humidity.
Adults are sexually dimorphic and while ‘spider beetles’ are very distinctive and readily recognized there are lots of superficially similar species and so they will need to be looked at very carefully. In both sexes the eyes are spherical and protruding (much more so in the male) and the antennal insertions are very close together, the pronotum is smooth laterally (without teeth or denticles) and strongly constricted in the basal third and the elytra have strongly punctured striae complete to the apex. The pronotal surface is uneven and variable; it is strongly raised in front of the base and weakly elevated towards the lateral margins in both sexes although the lateral elevation may be larger and much more distinct in the female. The size varies widely, 2.0-4.3mm, and females are on average much larger than males. The male is elongate and narrow with the elytra gradually and rather weakly dilated towards a continually rounded apical margin, the legs are very long and slender with the basal tarsomere much longer than the others, the pronotum is finely pubescent and this may form two longitudinal stripes on the disc, the elytral pubescence is very fine and even across all the interstices and it may form two transverse bands, one near the base and one near the apex. The female pronotum is finely pubescent and has two variously-developed longitudinal stripes of dense creamy setae forming a U or V pattern, the elytra are elongate-oval and widest about the middle with short, sparse pubescence evenly distributed across all the interstices and there are usually two transverse bands of denser pale pubescence, one near the base and one near the apex. The female legs are more robust and proportionally shorter than those of the male, the antennae are filiform in both sexes but shorter and thicker in the female (about three quarters the body length); the male antennae being longer than the body.