Meloe violaceus Marsham, 1802
Violet Oil Beetle
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POLYPHAGA Emery, 1886
TENEBRIONOIDEA Latreille, 1802
MELOINAE Gyllenhal, 1810
MELOINI Gyllenhal, 1810
Meloe Linnaeus, 1758
This very widespread species occurs throughout the Palaearctic region from Portugal to the far east of Russia, it is also widespread across North Africa and the Near East and is generally the most common species in Europe, reaching far beyond the Arctic Circle and present to the far north of Sweden, it is most common in lowland areas but extends to about 1500m in most European mountain ranges. In the UK it has suffered a drastic decline since the 1960s and is absent or very local and rare from many eastern areas of England, it is still generally common in the West Country and throughout Wales but very rare in the north, it remains locally common throughout Scotland though slightly less so in the east. More eurytopic than our other oil beetles, M. violaceus occurs in flower-rich grasslands, especially near the coast, heathland and moorland and open woodland margins and glades; adults are active over a relatively short period from March to June, usually peaking in abundance in April, and may be found in warm sunny weather among long grass or on flowers, especially lesser celandine (Ficaria verna Huds.) where they will often gorge themselves on the foliage, and in bright sunshine they often remain stationary, sunning themselves on pathways and grass stems etc. Mating occurs through the season and mated females dig burrows into soft dry earth to lay large batches of eggs, between 2000 and 10000 have been recorded, these are usually shallow, at most a few inches in depth, and once excavated she will back out and enter abdomen first, lay her eggs and then back-fill the hole. Oviposition can be a frantic business and several females may be seen digging within a small area, sometimes unearthing eggs laid by a previous female, and this continues through the season. Tiny black (those of M. proscarabaeus are mostly yellow) and louse-like triungulin larvae about 2mm in length hatch within a few weeks and emerge en-masse from the soil, they are very active and run rapidly around looking for suitable stems to climb, large numbers will climb any suitable flower stem and assemble in a tight cluster waiting for visiting insects, many will be carried off by flies and wasps etc but any visiting bees will quickly become infested and transport the parasites back
to their nests. Hosts include various solitary bees, mostly of the genera Andrena Fabricius, 1775, Halictus Latreille, 1804, Colletes Latreille, 1802, Osmia Panzer, 1806 and Lasioglossom Curtis, 1833. Once in the nest the triungulin leaves the bee and enters a larval brood cell where it will consume the egg or tiny larvae and enter into a quiescent stage to moult and emerge as a scarabaeiod-form larva which will develop through the summer, consuming the contents of the cell and sometimes entering adjacent cells to continue feeding, they pass through many instars as they grow but after an autumn moult the enter a quiet overwintering stage which will moult in the spring, once more producing a scarabaeiod-larva which may either continue feeding for a while or pupate directly to produce an adult in early spring. Oil beetles are generally slow-moving insects that rarely react to being handled other than by producing a noxious liquid from the leg joints, so-called reflex-bleeding, than some people find highly irritating.
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Oil beetles are quite distinctive among our fauna and should not be confused with any other genus. Adults of the present species vary widely in size, from about 10 to 33mm, and may often be recognized in the field by their rather bright metallic blue reflection but entirely black individuals occur and so confusion with our other common species, M. proscarabaeus, which may also have a blue reflection although here it is usually weaker. Among our UK oil beetles the present species may be identified by the form of the pronotum; quadrate to slightly elongate with a transverse impression in front of a distinctly angled and indented basal margin which has a small but distinct and sharp tooth at the posterior angles. The forebody is finely and rather densely punctured and the elytra very finely punctured and strongly microsculptured and rugose. Males may be recognized by the strongly-angled joint between antennomeres 6 and 7 (which are less dilated when compared to those of M. proscarabaeus), this ‘kink’ is also present in the female but to a much lesser extent. Our other oil beetles are generally very local and rare and, with the exception of M. autumnalis Olivier, 1792, which lacks the transverse basal pronotal furrow, all have the pronotum strongly convex.