Dienerella filum (Aubé, 1850)

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POLYPHAGA Emery, 1886

CUCUJOIDEA Latreille, 1802

LATRIDIIDAE Erichson, 1842

LATRIDIINAE Erichson, 1842

Dienerella Reitter, 1911

Native to the Palaearctic region, this species is now more-or-less cosmopolitan in distribution, having made its way around the world along with human transport and trade. The species occurs in the wild throughout Europe although it is sporadic and generally very local and rare, but it is strongly synanthropic and much more frequently recorded  in association with humans; there are records scattered throughout England and a few from Scotland and Ireland and all are from houses, outhouses, museums and warehouses etc. Typical habitats are older houses, basements and commercial properties, and in many temperate areas it is among the most common of domestic pests. Adults and larvae feed on slime mould spores and spores and hyphae of filamentous fungi and so generally occur in damp and neglected places, often among mouldy foods and other organic matter, among damp wood around doors and windows, damp plaster around cold water pipes and under wallpaper that is starting to lift. They may also become established in air-conditioning or refrigeration systems and they sometimes become established in neglected outhouses. Adults are sometimes attracted to old houses and other buildings that are being renovated and here they may quickly become established, they tend to appear in numbers several months after they arrive and start breeding and, unless checked, they usually form large populations, in this way they have been linked to hygiene problems in recently renovated parts of hospitals. Adults are brachypterous and so dispersal occurs by walking and mating can occur at any time given suitable conditions. Females lay eggs singly or in small batches in dark concealed places among suitable host material, this may continue over a long period and each will produce about twenty eggs. Larvae emerge after a few days and their development depends on temperature and humidity, but at 24°C the cycle from egg to adult can be as short as 21 days, at 18°C it takes about 54 days and at lower temperatures can take three months. The species can be very difficult to detect,; the larvae are at most 2mm long when fully-grown and the pupae about 1 mm, and both stages tend to be well concealed, but adults sometimes appear on walls, especially around windows and external doors, and, as they cannot climb smooth surfaces, they often get trapped in sinks and baths.

Dienerella filum 1

Dienerella filum 1

© U.Schmidt

Dienerella filum 2

Dienerella filum 2

© Lech Borowiec

In the wild the species generally occurs among stored or neglected hay and straw, it may be common among animal feeds and grain and it often becomes established on mouldy wood, under bark or among decaying sporocarps. Under these conditions it is a seasonal breeder although the number of broods is dependent on environmental conditions. In a few instances the species has been found in abundance in old zoological collections and apparently sealed herbariums, which might suggest it is capable of extended quiescent periods.

1.50-1.65 mm. Although tiny this species should be readily identified from the general appearance; elongate, narrow and discontinuous in outline with coarsely-sculptured pronotum and elytra, glabrous and entirely pale to dark brown or with the forebody darkened. Head long and broad in front of convex eyes, which have large and individually strongly convex facets, temples short and strongly converging, usually hardly visible, Surface strongly sculptured; usually with an impunctate triangular impression from the base which may extend forward beyond the anterior margin of the eyes surrounded by raised and punctured cuticle from inside the eyes and an explanate lateral and anterior margin. Antennae inserted anteriorly, remote from the eyes, 11-segmented with a 2-segmented club, basal two segments expanded and segments 3-9 narrow and elongate. Pronotum transverse, broadest behind rounded anterior angles and narrowed to near-perpendicular posterior angles that usually possess a few very small teeth, explanate margin broader towards the apex, surface roughly sculptured and broadly impressed across the basal half. Elytra elongate, about 2:1, and gently curved from angled and finely-toothed shoulders to a continuous apical margin, surface with strongly and deeply punctured striae which often more or less obliterate the interstices, often with weak or only partially distinct keels on the first and fifth intervals. Legs slender with all femora of the same width and tibiae only weakly expanded from the base. Tarsi 3-segmented, all segments simple, the basal segments short and inconspicuous and the terminal segment long and curved. Claws smooth and lacking a basal tooth.