Description

This subfamily includes some of the largest and most massive of all beetles; males of some species of Goliathus exceed 100mm and are otherwise very broad and heavily sclerotized, and many tropical species exceed 50mm but the majority are smaller, between 15 and 30mm in length; the smallest and largest European species are Valgus hemipterus (5-10mm) and Osmoderma eremita (Scopoli, 1763) (24-30mm). Colour and pattern vary enormously although in northern temperate regions most are black or various shades of green, metallic or otherwise, and most lack distinct patterns-species of Trichius or the American Euphoria fascifera LeConte, 1861 being notable exceptions-and many species in warmer regions are also black or otherwise drab, but the group is generally desirable, at least in large part, among collectors and commercially-interested parties due to the strikingly patterned and brilliantly colourful and metallic appearance of tropical species. Variation in colour and pattern is a feature of many species and has given rise to a mountain of often confusing sub-specific names, similar things happened among other popular groups such as longhorns and larger ground beetles but the heyday for this sort of thing seems to have passed and most names-other than valid sub-specific names-have become redundant and are largely ignored, but it is easy to understand why such named were used as a well-laid out and labelled drawer of metallic chafers is a truly satisfying thing. Yellow, green and coppery or violet are common in tropical species, blue much less so, and many are polychromic in the sense that they may appear yellow, green or blue depending on the angle from which they are viewed, most patterns consist of contrasting maculae , streaks or margins and the straightforward bicoloured forebody/elytra arrangement seen in many families is unusual, the size and extent of maculae and spots can vary widely in a single population of a single species and in some e.g. species of Marmarina Kirby, 1827, the entire body is covered in tiny contrasting spots of colour. A good idea of colour and pattern variation can be seen in the genus Pachnoda Burmeister, 1842, these are commonly known as sun-beetles and one species, P. marginata (Drury, 1773) along with about 10 subspecies, is widely available for rearing as larvae, pupae or adults in many fascinating colours. Old World Goliath beetles, prized among collectors and the like, are very varied but most are easily recognized by their distinctive pattern of pale lines on a dark red or brown background, and some Neotropical members of the genus Gymnetis MacLeay, 1819 must surely qualify among the most beautifully coloured and patterned of all beetles. Most species are largely glabrous, and pubescence is more common on the underside or the legs but some tropical groups e.g. species of the South African genus Trichostetha Burmeister, 1842, most of which live at high altitudes, have long but sparse pubescence while members of the Australian genus Trichaulax Kraatz, 1880 have lines of dense pubescence on the elytra and Afrotropical species of the large genus Microvalgus Kraatz, 1883 have distinct scales both dorsally and ventrally. Shape also varies hugely but typically they are broadly-oval and rather flattened dorsally, the head is narrow and the pronotum transverse, widest about the base and narrowed to a rounded anterior margin, the elytra are broad and parallel-sided with distinct shoulders and leave the abdominal apex exposed. More technically the group may be diagnosed as follows. Head small, usually with large convex eyes and lacking temples (from above), the vertex is simply convex, the frons and clypeus simple or variously impressed and the labrum weakly sclerotized or membranous and usually not visible. In most the mandibles are small, relatively diminutive and usually hidden under the clypeus or other mouthparts, and the eye-canthus is long and narrow. Antennae 10-segmented, short and distinctly clubbed; the scape is broadened and variously modified e.g. in the Cremastocheilini it is dilated into a broad triangular plate, the pedicel is smaller and the flagellum 5-segmented, the club consists of 3 elliptical  and closely approximated segments which in tropical species may be very elongate. Pronotum very variable but usually transverse to quadrate and with distinct lateral borders; typically somewhat semi-circular with a sinuate basal margin but in many exotic forms the overall shape is transverse-pentagonal or hexagonal, often with the basal half parallel-sided or nearly so, in most the basal margin is sinuate and closely approximated to a large or very large scutellum but in Gymnetini it is produced back medially into a long lobe and the scutellum is not visible. The pronotal surface is usually smoothly convex but in some groups e.g. among the Valgini there are patterns of impressions or callosities. The prosternum is very variable but is typically smooth with closed and transverse, closely approximated coxal cavities placed in or towards the anterior half, in some groups there is a well-developed process between the coxae and the anterior margin is variously projecting. The mesosternum is short with transverse coxal cavities separated by an anterior projection of the metasternum and well-developed mesepimera, the metasternum is long and variously produced, sometimes very strongly so, into a broad lobe which projects forward between or above the middle coxae (this is very strongly developed in some groups e.g. Goliathini), the metepimera are long and narrow and the posterior margin rarely projects far between the hind coxae. In most the hind coxae are quite closely approximated (almost contiguous in Trichiini) and widely transverse, reaching the lateral margin, but in e.g. Valgini they are widely separated with the meso- and metasternal junction lying between. Abdomen usually with 7 distinct sternites and the pygidium exposed and immovably fused to the propygidium. Scutellum long and triangular in Cetoniini, variously shaped in other tribes. Elytra usually broad, rather parallel-sided and flattened dorsally, in most the shoulders are well-developed and the apical margin in continuously rounded, they mostly lack distinct striae, although in many there is a variously developed sutural stria and many have longitudinal impressions or ridges and in some groups the areas between these are variously pubescent. A well-developed post humeral emargination which allows the flight with the elytra closed is present in Cetoniini and Gymnetini but absent or less strongly developed in other tribes, this is coupled with an ascending and convex mesepimeron which is usually visible behind the posterior pronotal angles from above, again this is usually absent or wanting in other tribes. The legs are usually long and always very robust; the front coxae are convex to some extent and often strongly conical, the trochanters are long and obliquely connected to the femora which are usually broadly rounded and smooth although in some tropical groups they have apical projections which fit into basal internal angles on the tibiae when the legs are retracted. In many species the hind femora are larger or more developed than the others, an extreme example of this being seen in the Neotropical genus Blaesia Burmeister, 1842 (Gymnetini). The tibiae are long and well-sclerotized, the front tibiae often the longest, as seen in some Mexican Neoscelis Schoch, 1897, and usually with various external teeth or at least tubercles or spines towards the apex, the middle and hind tibiae also have external teeth or ridges but usually only one or two sets and there is often a longitudinal series of punctures along the inner margin, the inner apical angle has two long spurs and the outer angle may be produced into a ridge or armed with spines. The tarsi are usually 5-segmented although in the Afrotropical subtribe Trichoplina Krikken, 1985 (Cremastocheilini) they are 3-segmented, with all segments simple and robust, and all have paired claws which are nearly always more-or-less equal in length. This description is very general and the group varies hugely in detail but with a little experience the majority of species are readily recognized, among our UK chafers they may be distinguished by exposed pygidium, paired and equal claws which lack lateral teeth or lobes, and paired hind tibial spurs.