Achopera alternata Lea, 1910
This small and elusive saproxylic weevil, native to New South Wales and Tasmania, is recorded from two UK sites; Denbighshire in Wales where a single specimen was found in 1998, and Hertfordshire in England where it was discovered in 2007 and is now established, these are the only known records of the species outside its native range. The Hertfordshire colony is present in long-established wooded parkland with many mature broadleaf and coniferous trees and an abundance of decaying timber; it is also very local to the authors and so is regularly sampled for coleoptera. Our first record of Achopera was among an extraction sample taken from a rot-hole in a fallen mature Fagus in 2007 and this remained our only record until 2014, surprising perhaps considering the time we spend looking for beetles in the park. In February 2014 a further specimen was extracted from similar material taken from an old hollow Fagus stump some 150 metres from the original discovery and since that time we have found adults among similar samples from the same stump throughout the winter months. Adults seem to like very dry and powdery a few cm below the surface and sometimes present among spider webs or alongside other beetles. Nocturnal examination of the stumps through the spring of 2014 revealed small numbers of adults on the surface of the wood, the highest number observed was ten; they move slowly out of cracks in the timber late in the evening and remain still on the surface, when several are present they usually remain remote from each other and we have not observed any interaction, even when they are close together, when disturbed they either remain still or move very slowly, prompting our common name of ‘sloth weevil’. Because of this, and due to their appearance, they are very difficult to discover and when looking at new sites a very careful nocturnal examination of dead and denuded beech trees is probably the best way to find them. On several occasions they seem to have been grazing on algae or fungi on the wood but they move very slowly and so this was not convincing. In 2017 we discovered another nocturnal specimen, this time on the surface of an area of dead wood on an otherwise healthy Quercus about 100 metres from the Fagus colony.
Achopera alternata 1
Achopera alternata 2
Achopera alternata 3
Achopera alternata 4
Both these finds have been close to avian nests and in both cases we have disturbed birds from these nests at night, this suggests to us that the beetles may disperse by phoresy to sites where conditions for them are ideal i.e. in dry rot holes beneath nests, in which case they might not be fussy regarding which species of broadleaf tree they colonize. This idea is strengthened by the appearance of the weevils; with their hooked tibiae, curved claws and the way the legs are bent in life-the apico-ventral part of the femora are excavate to partly accommodate the tibiae-they are strongly reminiscent of lice and it is very easy to imagine them clinging to feathers. In the absence of another explanation it is difficult to imagine how such a sluggish species is able to disperse over hundreds of metres, in life they do not retract the legs or display thanatosis when disturbed; they remain still or move slowly and give the impression of not being at all bothered, this behaviour might be in response to a general lack of predators as we often observe them in close proximity to large spiders. Pairs of adults have been kept in containers among apparently suitable substrate during the spring but mating has not been observed.
Adults are very distinctive and should not be confused with any other species. 5-6mm, entire body and legs brown, mottles with darker transverse markings. Head transverse and mostly hidden under the anterior pronotal margin, with large weakly convex eyes and a short, almost parallel-sided rostrum which is covered with scales to the antennal insertions. Antennae short with the scape expanded in the apical half, a 7-segmented funiculus and rounded club. Pronotum transverse, broadest behind the middle and constricted before a raised anterior margin, posterior margin sinuate. Prosternum long in front of large, widely-separated and circular coxal cavities; with a wide and deep rostral channel reaching the posterior margin. Scutellum small but distinct, with curved lateral margins and an obtuse apex. Elytra parallel-sided with prominent shoulder and continuously rounded apically, deeply impressed and strongly punctured striae and raised third, fifth and seventh interstices. Femora without ventral teeth; excavate towards the apex to partly receive the tibiae, all tibiae with an incurved and sharp apical tooth. Tarsi robust; the two basal segments elongate and expanded apically, the third bilobed and mostly enclosing the small fourth segment, terminal segment long and curved. Claws free; smooth internally, curved and sharp. Males differ from females in the narrower and more strongly curved rostrum and the weakly depressed basal abdominal ventrites; in the female they are flat.