Hylecoetus dermestoides (Linnaeus, 1761)   Notable B


The NBN map shows modern records throughout England and Wales above a line from the Severn estuary to Warwickshire and the Humber north to the lake district and there are two single records; from the Scottish Highlands and (pre 1980) north Devon. Such a distribution suggests that our Watford records might be remarkable but Alexander (and 2004) quotes records from a few sites in southwest Surrey in 2001 and speculates whether these represent an expansion to the British or continental range or are an accidental introduction with imported timber. Our Watford records can only add data to the debate; the species is common (most years) throught the Whippendel wood complex and we have recorded them each year since 2003. Adults have been found locally between early April and June and numbers fluctuate between years, they generally occur along wooded margins eg along Rousebarn lane and around the few areas of open grassland in the woods and we have observed them in flight on many occasions. Sweeping marginal herbage is probably the easiest way to observe them. All the beetles we have observed have been females but a pupa found beneath the bark of a fallen and well rotten fagus trunk below Cassiobury park in early March 2009 produced a male on 14/4/09. (Surely it is difficult to imagine this population arising from an importation?)
Joy gives simple England, Scot 4 (N.E.); very local (was he aware of more southerly records?) while Fowler's records- Sherwood forest, Manchester area, Cannock chase and the Scottish Highlands where it is a rare insect from 'Scotch Fir', Tay district- are more in line with modern ideas.
Hicken States that the species is so uncommon in Britain that it cannot be considered as an important pest of timber, in Europe, however, there have been instance of extensive damage to Oak and Beech and it is thought that the species assists in the spread of wood destroying fungi. An account of various aspects of the species biology is given and the following summary is taken from this source.

The beetle occurs in a variety of hardwood (broadleaved) and softwood (coniferous) trees and particular mention is made of Beech and Oak but Maple, Alder, Fir, Pine, Larch, Spruce and Douglas fir may also be hosts. In Finland it has been recorded as especially common in Birch. More than twenty species of timber have been recorded as 'attacked' by the beetles.
The adult stage lasts for only a few days and occurs between early April and July. Eggs are laid in batches, generally between four and ninety and a single female was recorded as laying 146 eggs, in wood crevices, bore holes or among the rough bark of dead logs or stumps etc. Larvae emerge within one or two weeks and consume part of the chorion which hosts a symbiotic fungus. They remain together for a while before dispersing to find suitable places to begin boring into the wood. Their galleries are unbranched and curved and extend through into the 'heartwood' (xylem) of Oak, Pine and Larch while the heartwood of Beech is said not to be penetrated. Larvae feed on the fungus Endomyces hylecoeti which grows on the tunnel walls and which was introduced by the young larva from its chorion. These borings may penetrate to 20cm and are widened by the larvae to accomodate its growth, the distendable prothorax is used to assist movement within the tunnel and the larva is able to turn around in order to eject frass although this is usually carried out using the long terminal segment. During the winter the tunnle is sealed with a plug of wood dust, this is removed in March when tunnel widening recommences. Prior to pupation the larva constructs a wider chamber close to the ingress hole and seals the internal end with dust. The pupal stage is said to last for only a week but our pupa, which was motile and so presumably freshly formed, took about four weeks before the adult hatched. The adults are said not to feed (although we have observed them on umbel flowers) and the life cycle takes either one or two years. Hurka states the the species is univoltine.

On 18/08/09 while examining decayed wood pulp beneath the bark of a fallen scots pine in Whippendell wood, a single Hylecoetus larvae was found in the cubcorticol galleries of Dryocoetes autographus and Hylurgops palliatus (both Scolytinae, Curculionidae), many early instar larvae of both scolytids were present, and the Hylecoetus larva must surely, at around 2mm, have been first instar.

This is a large and distinctive species which will soon become familiar in the field; superficially similar to several cantharids but with shorter antennae and long tarsi without lobed segments. They move rapidly in the sweepnet and need to be grabbed quickly for examination. The male is immediately recognised by the greatly enlarged maxillary palps which are constantly and rapidly moving even when the beetle is at rest. Joy remarks of both our Lymexylid species that they occur around dead and dying trees in June at sunset.

6-11mm (Joy) females are generally larger. Female entirely orange/yellow with the antennae darkened apically. Male with head, palps and antennae, prothorax, scutellum, abdomen and elytral apices black. In both sexes: head narrowed in front of and behind prominent round eyes. Surface with dense wide and shallow puncturation and erect yellow pubescence. Centre of vertex raised into a sharp tubercle. Antennae serrate; weakly so in female, more strongly in male, inserted in front of eyes. Palps of normal size in female with terminal segment truncate, in male with second and third segments greatly enlarged with brush-like appendages apically. Pronotum transverse, lateral and front margin curved, hind margin sinuate and finely bordered. Surface roughly sculptured, in the male with an obscurely deliniated tubercle either side of middle. Finely punctate and pubescent, more densely so towards edges. Scutellum densely punctate and pubescent, as surrounding elytra, with a raised keel which is shiny and impunctate. Elytra elongate but not covering abdomen, with prominent shoulders and gently sinuate side margins (this is reminiscent of some Oedemeridae), diverging apically. Upper surface densely punctate and with almost recumbent pubescence obliquely directed away from the suture. With (sometimes obscurely) raised longitudinal ridges, the two nearest the suture unite about 3/5 from the base. Wings full. Legs long and slender. Male femora to some extent darkened. Not sexually dimorphic. Tarsi 5-5-5, all segments elongate. Claws smooth and gently curved, with a well developed and sharp tooth at base in both sexes.

Description from two Watford species (male and female)

Alexander, 2004. Revision of the index of ecological continuity as used for saproxylic beetles. English Nature Research reports 574. English Nature, 2004.

Note: The male specimen pictured to the left was from the pupa mentioned above. It appears to have had some problems in emergence, the elytra are not typical and would normally be more complete.