Octotemnus glabriculus (Gyllenhal, 1827)
This generally common and often abundant species occurs throughout Europe and western Asia to the far north including Scandinavia and the U.K.; here it is common throughout England and Wales but more scattered further north to the western and northern Scottish Highlands. Often found alongside Cis bilamellatus, these are by far our most common U.K. ciids occurring through the spring and early summer wherever suitable host fungi occur e.g.in wooded areas, parks and gardens etc. The principal U.K. host is Trametes versicolor but other species of also host the beetle e.g. T. gibbosa, T. ochracea, T. pubescens and Laetiporus sulphureus, and on the continent it is also recorded from other fungi; Stereum hirsutum, Phanerochaete velutina, Hypholoma fasciculare and Bjerkandera adusta, all of which occur in the U.K. The occasional record from birch polypore is probably incidental as this fungus is annual and tends to dry out in the summer, making it unsuitable. Adults occur year-round; through the winter within the damp and decaying tissues of fruiting bodies on trees and stumps of a wide range of broadleaf species, and in the spring they disperse, healthy fungi are ignored but the beetles are strongly attracted to damaged and decaying specimens and they are among the first ciids to colonize fruiting bodies early in the year, breeding commences immediately* and huge populations develop by late spring and early summer, the beetles prefer moist fungi and tend to leave those exposed to the sun as they dry out in the summer. Later in the spring, when Octotemnus is firmly established, they will usually be found alongside the common and widespread Cis boleti; this species prefers drier fruiting bodies and will persist through the summer after Octotemnus has left drier specimens. Late summer and autumn may again produce large numbers of adults; pale specimens, presumably immature, occur from April to October but seem to be most abundant in the spring and autumn. Adults will only rarely be seen on the surface of the fungus and they are not attracted to light, tapping likely host material over a sheet may produce a few specimens, but to appreciate the abundance of the adults a sample will need to be carefully pulled apart under a lens or, better, subject to heat extraction but this may be destructive as a good sample may produce many hundreds of specimens. Octotemnus is specifically attracted to compounds produced by Trametes when it is damaged or in a certain stage of decay and large numbers may appear quickly and begin breeding in just about any situation, the effect of such feeding may reduce the fecundity of the fungus by reducing its reproductive potential although in general the beetles will arrive after the spores have been shed. Fungal tissue is rich in carbohydrate and protein and several metallic elements become concentrated here and so Octotemnus may play an important part in the recycling of woodland nutrients.
Octotemnus glabriculus 1
© Lech Borowiec
Octotemnus glabriculus 2
Although Octotemnus may appear nondescript and dull it will soon become distinctive among other ciids even in the field; the very convex and shiny appearance is obvious once a few specimens have been identified. Specimens are best mounted lying sideways on fine card points with a few appendages teased out for inspection, and then antennal segments are thus readily counted. 1.5-2.0mm easily identified from the 8-segmented antennae and the small size. Antennae yellow with the club dark when mature, segments 1 and 2 large and rounded, 3 elongate and as long as 4 and 5 together, 4 and 5 quadrate, 6-8 form a loose and pubescent 3-segmented club. Entire body, when mature, dark brown to black and shiny. Head and pronotum finely punctured and microsculptured (X50). Head declined but visible from above, with an oblique carina from the anterior margin of the convex eyes to the labrum, covering the antennal insertions. Pronotum highly arched and finely bordered. The elytra with very fine granular microsculpture, making them appear more shiny than the foreparts; finely bordered and randomly punctured, this may be evanescent towards the base where the surface becomes strigose, and with sparse outstanding setae towards the apex. The legs are pale with the outer margins of the tibiae spinose in the apical half; tarsi 4-4-4, segments 1-3 tiny and with long white pubescence below, the fourth segment as long as 1-3 combined. Claws smooth and weakly toothed at the base.
*It may be that this species breeds continuously through the winter as we extracted a few adults along with many larvae from an old and damp sample of Laetiporus sulphureus taken from a Watford park on 18/2/2017.