Anthrenus verbasci (Linnaeus, 1767)
Varied Carpet Beetle
POLYPHAGA Emery, 1886
BOSTRICHOIDEA Latreille, 1802
ANTHRENINAE Gistel, 1848
Anthrenus Geoffroy, 1762
Nathrenus Casey, 1900
This notorious pest species is native to the Western Palaearctic; Europe, North Africa, The Near East and Northern Asia but the modern distribution is cosmopolitan due to the world-wide trade in foodstuffs etc., it was first recorded in the United States around 1850 and is now widespread throughout North America and Canada. In the U.K. it is the most common member of the genus, being generally common and often abundant throughout south and central England and Wales north to Lancashire and there are scattered records from Southwest Scotland. Adults occur from mid-May until August and may be swept from foliage or found on flowers, especially those of umbels, where they feed on pollen and nectar; they fly well and so may occur in just about any situation but are generally associated with open areas with plenty of flowers and trees. In the sweep net they may remain inactive for some time with the appendages held tightly against the body. Mating occurs throughout their season and eggs are laid in dry situations e.g. in the detritus below avian nests in tree hollows, hymenopteran nests and often among stored products in houses etc. The common name refers to the larva’s ability to feed natural carpet fibres but more generally they infest and consume a very wide range of materials and stored products of both animal and plant origin; wool, silken and cotton fabrics, fur, hair, horn, cereals and dried fruit and vegetables of all kinds, nuts and even stored clothing etc. etc. in houses they infest debris and spider-webs in air-conditioning systems and secluded corners, feeding upon dead insects and debris, a habit which mimics the wild behaviour of living among nests in trees, the adults facilitate this behaviour as around the time of egg-laying they are photophobic and seek out dark and secluded habitats. Museum collections and artefacts in general are prone to infestation but particularly collections of dried insects; a new specimen added to a box or drawer may contain eggs, larvae or pupae which will continue developing and breeding eventually reducing the entire contents to dust and fragments, infestations are easily detected by the presence of shed larval skins or damaged specimens but with large collections it is sometimes impractical to examine every drawer regularly, in the past various toxic aromatic chemicals
were used to kill or deter Anthrenus but nowadays we rely on air-tight containers to keep infection out or deep-freezing to kill suspected beetles. It is the larvae that do the damage as adults consume only nectar and pollen. In the spring and early summer adults fly high above the ground and may enter premises through roof vents, joins in soffits etc. or through open windows, and an infestation will often begin in an avian nest in the roof and then spread to other parts where host-material is available, and adults found around windows or on walls during the day or evening may indicate a larger local infestation. The life cycle is generally spread over two years but may extend to three or more depending on conditions and late instar larvae may enter an extended diapause which might be photoperiodic or it may be due to other factors. Adults are generally attracted to light and each female will lay about forty eggs among suitable host material over a week or two, the incubation period is dependent on temperature; at 15°C it may exceed seven weeks whereas at 30°C it is about twelve days. The very characteristic larvae which are sometimes seen wandering on fabric or carpets or detected by their shed skins, develop slowly and generally pass through seven or eight instars although this can vary between five and sixteen, lack of food or moisture etc. may induce dormancy but in any case when fully-grown they will diapause before pupating, the length of this depends on environmental factors and under artificial conditions pupation may occur at any time of the year. Larval development has been recorded taking between 220 and 320 days and the pupal stage between 10 and 30 days under good conditions. Under natural conditions i.e. outside, larval development is spread over two summers with feeding and growth occurring during warmer seasons; the first summer as a small larva which will overwinter, and the second culminating in a fully grown larva which stop growing, overwinter and pupate in the spring. Adults have been recorded living between 14 and 44 days.
When mature the larva measures 4-5mm and is very characteristic with a series of light and dark brown transverse strips of pubescence, and unlike other species they are broadest towards the apex. They have long legs and can move relatively quickly, when alarmed they adopt a defensive posture by raising the abdomen and spreading three tufts of bristles located either side towards the apex of the abdomen.
A number of varieties occur which differ in size, shape and the colour and pattern of the scales but generally the adults are 1.7-3.5mm and have a pattern of pale white, brownish or yellow elongate scales arranged in transverse, angled bands on the elytra and at the base of the pronotum against a background of darker brown to black scales throughout. The head is small and often concealed below the anterior margin of the pronotum, the eyes are round, not emarginate, and the antennae 11-segmented and entirely black; the 2 basal segments are large, quadrate and rounded, 3-7 transverse, 8 transverse but wider than 3-7, and 9-11 form a 3-segmented club; 9 transverse and narrower than 10 and 11 which are much larger, the terminal segment rounded apically. Pronotum broadest at the base and strongly narrowed anteriorly, the posterior angles (from above) acute, the basal margin strongly sinuate and produced backwards medially. Elytra completely covering the abdomen and continuously rounded apically. Ventral surface with fine long grey or yellow scales throughout.