Dendroxena quadrimaculata (Scopoli, 1772)
POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
SILPHINAE Latreille, 1806
DENDROXENA Motschulsky, 1858
Dendroxena Motschulsky, 1858 is a small genus of 4 Palaearctic species, only one of which occurs in Europe; with the exception of the far north D. quadrimaculata is generally common throughout, including the Mediterranean islands, and extends east through Asia Minor, Ukraine and Russia to eastern Siberia. In the U.K. it is locally common throughout England and Wales and there are a few records from south west Scotland but, as in Europe generally, it is thought to have declined over recent decades. The adults are unusual for silphids in that they are arboreal and active predators of both adult and larval insects; they occur from late April until July, and again in the autumn when they may be active for a while before entering leaf litter or moss etc. to overwinter, or conversely they may eclose and remain in subterranean cells until the spring. The typical habitat is deciduous woodland where they seem to prefer oak but may occur on a range of trees, they are active nocturnally and hunt Lepidoptera larvae by following scent trails; they fly among the branches and are known to hunt a range of leaf-rollers, Tortrix Linnaeus, 1758 etc., geometrids generally but especially species of Erranis Hubner, 1825, and the winter moth, Operophthera bumata (Linnaeus, 1758). On the continent they are well known for hunting processionary moth larvae, Thaumetopoeidae Aurivillius, 1889 (formerly Notodontidae), and for this reason they were introduced to the United States as a possible biocontrol agent of the gypsy moth, Lymantria dispar (Linnaeus, 1758) but they failed to establish. Although primarily nocturnal and mostly confined to the canopy they are occasionally active among foliage or they may visit flowers e.g. umbels or those of Sorbus aucuparia L. in hot weather. The larvae are terrestrial and nocturnal, living among leaf litter etc. and hunting other insects and larvae, they are easily spotted by torchlight but are agile and may move quickly in pursuit of prey. Even among silphid larvae they are distinctive; shiny black with the head, legs and the terminal body segment red; broadest at the prothorax and gradually tapered to the apex, the thoracic segments are widely and strongly produced backwards and there is an arcuate depression on the prothoracic segment.
Dendroxena quadrimaculata 1
Dendroxena quadrimaculata 2
Among the U.K. fauna this large, 10-14mm, silphid is distinctive and should not be confused with any other species, the colouration is unique; entirely yellow with the head, appendages, 2 spots on each elytron, scutellum and pronotal disc dark. The head is transverse with prominent eyes and long, strongly constricted temples, the surface shiny and with fine punctation and sparse golden-yellow pubescence. Antennae inserted laterally on the clypeus, the insertions visible from above, basal segment long and curved, 2 and 3 elongate, 4-7 quadrate to weakly elongate, and 8-11 form a gradual club; segments 9-11 are finely and very densely pubescent. Pronotum transverse; rather flattened and variously impressed in the basal half, punctation fine and diffuse on the disc becoming denser towards the margins, rounded laterally and broadest behind the middle. The anterior angles are rounded and weakly produced, the posterior angles rounded to the basal margin which is straight in the median third and oblique laterally. Scutellum triangular and very large, with sinuate lateral margins. Elytra broadly elongate and completely covering the abdomen, the apices are separately rounded and the surface rather strongly and densely punctured, each with 3 longitudinal carinae from the base to the apical third, and strongly explanate. Legs entirely dark; the femora with fine dark setae, the tibiae curved and gradually broadened to the apex and each with longitudinal rows of stout setae and a strong apical spine. Tarsi 5-5-5; without lobed segments. Claws smooth, without a basal tooth.