Ocypus olens (Müller, O.F., 1764)
Devil's Coach-Horse Beetle
Measuring up to 32mm this is the largest of our U.K. species and among the largest of all staphylinids. It is native to, and generally common throughout, the Palaearctic and North Africa from Portugal to China and the far east of Russia, and it has been introduced, generally unintentionally, to many other areas e.g. North America, where it was first recorded in 1931, and much of Australasia. It is represented in the Azores by the subspecies O. o. azoricus (Méquignon, 1942). In the U.K. it is common throughout the mainland and there are many island records including the Western and Northern Islands. In Ireland there are a few records from the north. The species occurs in a wide range of damp but not too wet habitats e.g. woodland, parkland, wasteland and they are a common insect of urban gardens; by day they usually shelter among litter under logs and debris or in the soil and are rarely active, they are mostly nocturnal and are easily observed on pathways or around the base of trees or hedgerows, and may be common on calcareous grassland and even urban pavements. Adults occur year-round but are mostly active in the spring and early and late summer; during the warmest part of the summer they tend to remain inactive in cracks in soil or under debris. They predate a wide range of small animals e.g. slugs, worms, spiders and woodlice and are strongly attracted to carrion, sometimes in numbers; in our local park they are quick to attend any insects etc. that have been crushed on the pathways, and in this situation they are often to be found with numbers of nocturnal carabids. When feeding they continually masticate the food using the mandibles etc and the front legs, extracting the liquids and leaving the hard parts, earthworms etc are similarly consumed and the skins discarded. They overwinter in the soil and under logs or among litter, becoming active and feeding during mild spells when they are easily observes at night in suitable situations. When alarmed they adopt a threat-posture with the head and abdomen raised and their formidable mandibles opened wide, they can inflict a painful bite and will readily produce a foul-smelling defence fluid (olens means aroma or smell) from both the mouth and the tip of the abdomen. Mating occurs in late summer
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and autumn when the warmest weather has passed, and two or three weeks later the females begin to oviposit; the eggs which are large, up to 4mm in length, and white with a dark central band, are laid singly in the soil, among leaf-litter or moss, or under stones or debris. Larvae emerge after a month or so and will live in the same habitats as the adults, generally in the surface soil layers, and consume the same range of food, they can move rapidly and assume the same defence posture as the adults. They feed through the winter, passing through 3 instars; the first two are passed quite quickly as the tiny larvae grow but the third stage may last five or six months, during which time they will become almost as large as the adults. Pupation occurs in similar habitats and this stage lasts about a month, with new-generation adults appearing from early summer. Adults may be long-lived, passing two winters, and will usually increase in abundance through the summer as the new generation joins the existing population; when recording on a regular basis they may be noticed to vanish over a few days as they become inactive to escape the worst of the summer heat. They can run rapidly and may cover a considerable distance in a single night but dispersal is probably mostly by flight; they are strong fliers but this behaviour is rarely observed.
Among the U.K. species the distinctive size, shape and dull matt head and pronotum will soon become familiar. 20-30 mm, although slightly larger specimens occasionally occur. Broad, very robust and more-or-less parallel-sided; entirely black but for the terminal antennal segment and the palps which are to some extent pale. The dorsal surface is dull; the head and pronotum with strong microsculpture between moderately close and uniform punctation, and the entire surface with short and dense black or, rarely, red pubescence. The lateral margins of the head, pronotum and elytra have long and outstanding setae. Head transverse and a little wider than the pronotum; with small eyes that follow the outline, long temples and rounded hind angles. The mandibles very large, with at least one strong and usually blunt internal molar. Antennae longer than the head and not, or only weakly, thickened towards the apex, the insertions placed within the outer margins of the mandibles and separated further apart then the length of the basal segment; all segments elongate. Pronotum slightly elongate; lacking distinct hind-angles, more-or-less rounded posteriorly, and gradually narrowed to distinct anterior angles. Lateral margins finely bordered. Abdomen weakly rounded in outline, the tergites densely and evenly punctured but lacking the strong microsculpture of the foreparts. Legs long and robust; entirely black and with strongly spinose tibiae. Tarsi 5-5-5, the pro-tarsi strongly dilated.