LYMEXYLIDAE Fleming, 1821

Timberworm Beetles

These unusual beetles can be locally common in wooded areas, and are more likely to be found nocturnally. 

POLYPHAGA Emery, 1886 

LYMEXYLOIDEA Fleming, 1821

2

2

2

6-18mm

Suborder:   

Superfamily:

Subfamilies:

Genera:

Species:  

Size:      

Around the World

This is the only family included in the superfamily Lymexyloidea Fleming, 1821 and includes about 70 species in 9 or 10 genera and 3 subfamilies, it is an almost cosmopolitan group with the greatest diversity in the southern hemisphere. All species are wood borers and members of several genera e.g. the Nearctic Melittomma sericeum Harris, 1841 or the Palaearctic Elateroides dermestoides Linnaeus, 1761, are pests of commercially grown timber, and the Ship-Timber Beetle, Lymexylon navale Linnaeus, 1758, was formerly a serious pest of wooden ships and structural timber in Europe but changes in construction materials have negated its economic importance.

 

Hylecoetinae Boving & Craighead, 1931 includes 6 species of the single genus Elateroides Schaeffer, 1766, frequently referred to as Hylecoetus Latreille, 1806. The type species, E. dermestoides, is Eurasian and extends to the U.K. With the exception of E. lugubris (Say, 1835) which is Nearctic, all species are Palaearctic and one, E. flabellicornis (Schneider, 1791), extends to Taiwan. Lymexylinae Fleming, 1821 includes 4 genera. The type genus, Lymexylon, Fabricius, 1775, includes 6 species, of which the type, L. navale, extends to the U.K. Two species, L. amamianum Kurosawa, 1985 and L. miyakei Nakane, 1985, are Japanese with the former extending to Formosa, and the others are eastern in distribution. The monotypic Urtea Paulus, 2004 occurs in Greece. Arractocetus Kurosawa, 1985 includes 3 species from China, Japan and Taiwan. The remaining 25 species of the subfamily belong to the genus Atractocerus Palisot de Beauvois, 1801 which is pan-tropical with the greatest diversity in Southeast Asia; New Guinea and India are rich in species, and one African species, A. brevicornis (Linnaeus, 1766) extends to Madagascar. One species, A. atricollis Pic, 1955, has been reported from China and A. bruijni Gestro, 1874 is widespread in Southeast Asia north to Hong Kong. Several species occur in Australia and several are Neotropical. The monotypic Fusicornis Philippi, 1866 occurs in Chile. Melittommatinae Wheeler, 1986 is a pan-tropical group of 4 genera extending into southern Asia, Japan, Australia and the United States. Australymexylon Wheeler, 1986 includes 2 Australian species  while the 5 species of  Melittommopsis Lane, 1955  are 

Neotropical, the monotypic Protomelittomma Wheeler, 1986 occurs on Madagascar and the Seychelles. The largest genus of the group, Melittomma Murray, 1867, includes 17 species and occurs throughout the Southern Hemisphere extending north to India, Japan and Southeast Asia; many are confined to Southeast Asia or the Neotropics and one, M. sericeus, is native to the United States. At least two are endemic to Madagascar.

Description

Adult Lymexylids are small to medium sized beetles, 5-40mm, slender and very elongate, parallel-sided and at least to some extent dorsally flattened, most are drab coloured and finely punctured and pubescent. Most species are soft-bodied and superficially Cantharid or Clerid-like in appearance e.g. Elateroides Schaeffer, 1766, but some tropical forms are heavily-sclerotized and resemble Melandryids e.g. Melittomma Murray, 1867. The head is broad, short and visible from above, only rarely strongly deflexed, and with large or very large and conspicuous eyes which form the antero-lateral angle; in Melittomma they are very convex and occupy the entire side of the head, the vertex is smooth and variously, although usually finely, punctured and microsculptured, the only exception being the genus Elateroides where there is a small epicranial pit at the centre, and most species have long and curved or tattering temples; in Lymexylon Fabricius, 1775 they are constricted, forming a distinct neck. The antennae are 11-segmented and short, sometimes very short, filiform to serrate or, rarely, flabellate; when filiform the basal segment is generally elongate, the intermediate segments quadrate and the terminal segment moderately long and pointed, they are never expanded apically or clubbed. In some species they are sexually dimorphic. The mandibles are short and robust, rounded laterally and sharply pointed, the maxillary palps are 4-segmented and generally sexually dimorphic; simple in most females but elaborately developed in most males e.g. Elateroides where segment 3 is expanded into a large plumose structure, the palporgan. In some species they are much reduced or even missing in both sexes. The pronotum varies from transverse to elongate and is always near-parallel in form, the anterior angles tend to be only weakly-defined and the posterior angles near-perpendicular, the basal margin is often bisinuate and there are distinct lateral borders but never lateral teeth or spines. The surface is generally smooth, without any larger structure, although it may be weakly rugose or have small flattened tubercles or small raised areas, and in Atractocerus there is a deep longitudinal impression towards the base. The pro- and meso-coxae are cylindrical and projecting, the meta-coxae cylindrical and often produced posteriorly at the base or excavate to receive the femur, in some groups e.g. Lymexylon they extend laterally to the elytral margin while in others e.g. Elateroides they are shorter. The scutellum is always visible and sometimes characteristically sculptured. The elytra are generally elongate  and diverge from about the centre, the basal part usually having a locking mechanism along the suture, in many species they are individually tapered and separately rounded or pointed apically, the epipleura are usually poorly developed; broadest at the base and narrowing strongly, and in some species they are absent beyond the centre. The surface is smooth and lacking distinct striae, any punctation being very fine, but in most there are 3 or 4 longitudinal carinae which are often only poorly-defined and faint, but in Australymexylon Wheeler, 1986 they are well-developed and distinct. In some groups e.g. Atractocerus the elytra are much reduced, being about as long as the pronotum and much shorter than the first abdominal segment-Linnaeus named the type species Necydalis brevicornis in 1766! The abdomen is always to some extent exposed beyond the elytra and all segments are articulated and movable, the adults need to be seen when active to appreciate this. The hind wings are well-developed with a fairly complete venation, the radial cell being reduced or absent in some groups. The legs are long, slender and finely punctured and pubescent, the femora only weakly thickened, the tibiae long, narrow and almost parallel-sided; the pro-tibiae often with a comb of setae towards the apex but without an apical spur, the meso- and meta-tibiae have a short spur on the inner apical angle. Tarsi 5-segmented, without bilobed segments (c.f. Cantharids etc.), the basal segment usually the longest, 2-5 variously elongate. The claws small and curved, sharp and variously toothed at the base.

The larvae are distinctive with the head retractable into a hood-like prothorax, and the prothorax is distinctly larger than the meso- or metathorax. Antennae tiny, ocelli absent in later instars. Abdominal segments usually with lateral folds; segment 9 large and variously modified into a long, posteriorly oriented cutting structure or, in Melittomma, it is truncate and castellated along the posterior edge, like a saw-blade, segment 10 is smaller and situated beneath 8 or 9.

Ecology

So far as is known all species are saproxylic with larvae developing in galleries bored into wood; young larvae live under bark and later instars bore into the xylem. The larvae of many species have a symbiotic relationship with various types of fungi and these may be specific to species or genera, the fungi grow in the larval galleries and are tended by the larvae who in turn consume it. Larvae of Elateroides consume the fungus Endomyces hylecoeti, each egg is coated in fungal spores which are stored in a cavity near the ovipositor, and emerging larvae remain close to the egg for a while and so collect the spores before boring into the wood. The spores grow in the tunnels while the larvae keep them free of debris so ensuring a free supply of air which is essential for their growth. Species of Elateroides and Lymexylon are well-known as pests of hardwoods such as poplar, beech, oak and lime, the damage being done by the larvae as they burrow through the wood, but several others have also been serious pests of various trees e.g. Atractocerus kreuslerae Pascoe, 1864 was a serious pest of commercially grown eucalyptus timber in Australia during the twentieth century, and A. reversus Walker, 1858 was a serious pest of trees and manufactured timber products in India. Melittomma sericeum Harris, 1841 was formerly a widespread pest of chestnuts, and Protomelittomma insulare Fairmaire, 1893 caused damage to coconut palms in the Seychelles, with more than 75% of crop trees i.e. 95000 infested between 1953 and 1958.

UK Species

Head with an epicranial pit, temples rounded and not constricted into a neck. Antennae short; weakly serrate in the female, more strongly so in the male. Pronotum transverse, distinctly and diffusely punctured. Scutellum with a raised triangular carina. Elytra long, extending beyond the metacoxae. Male head, pronotum and elytral apices black. Female entirely yellow. Male with one or more visible abdominal sternites than the female. 6-18mm. Larval abdominal segment nine very long and narrow, heavily sclerotized with teeth along the dorsal edge.

Head smooth, temples narrowed behind the eyes forming a distinct neck. Antennae long; filiform in the male, weakly serrate in the female. Scutellum simple. Pronotum quadrate and very finely punctured. Elytra long, often covering the abdomen. Head black, pronotum variable, most often testaceous, elytra pale at the base and darkening towards apex, often abruptly so. 7-16mm Larval abdominal segment nine with a tooth at the apex.

All text on this site is licensed under a Creative Commons Attribution 4.0 International License.

For information on image rights, click HERE.