COLEOPTERA > POLYPHAGA > TENEBRIONOIDEA > Meloidae

Notwithstanding two rare and very localised non-native varieties, Lytta vesicatoria, the Spanish Fly, and Sitaris muralis, Flame-shouldered Blister Beetle, the British List records eight Meloe species. However, three of these species are almost certainly extinct, two have only recently been rediscovered, and one is very rare and nocturnal. That leaves just two species, Meloe proscarabaeus, the Black Oil Beetle, and Meloe violaceus, the Violet Oil Beetle.

You're more likely to encounter one of these flightless beetles by accident whilst out walking rather than by trying to seek them out, which has been nicely summed up by one author as "Meloe species are great lumbering beasts that lack wings, all are scarce, but because of their large size and strange form, they are often noted by general naturalists, much to the chagrin of coleopterists who hardly ever see them".  And, perhaps not surprisingly, that's exactly how I found the first individual I photographed as she just happened to be crossing the woodland path I was walking along. Their habit of seeking out bare ground in which to dig their nests means that they frequently transverse footpaths, so you should always be keeping a careful eye open when out in the countryside during March to July, although April and May seems to be the prime time.

They are commonly known as Oil Beetles or Blister Beetles as they have the ability, when disturbed or alarmed, to produce a bitter tasting oil from their knee joints containing the toxin cantharidin. The Meloe species are all nest parasites of solitary mining bees. Females dig their nest burrows in the ground where they lay hundreds of eggs. Once hatched, the active, louse-like, larvae, called triungulins, climb up on to flowers to wait for a suitable unsuspecting bee that they will latch onto. The bee will return to its nest to deposit the collected pollen and its uninvited guest, who will develop in the nest by eating the bee's eggs and food store until an adult emerges to start the whole process again.   

The Black and Violet forms can easily be confused as they are very similar, both around 30mm long when fully grown, and both described as being black with violet-blue reflections or all black in colour. The much rarer species, such as Meloe brevicollis, the Short-necked Oil Beetle, are more easily separable from a combination of size, general appearance and shape of the thorax, but Meloe proscarabaeus and Meloe violaceous can only reliably be distinguished by carefully looking at the back of the thorax. It is roughly square in both species, but in proscarabaeus it has an almost straight base with no depression and a very small rounded tooth, whereas in violaceous the lower edge is indented with a depressed area, and has a distinct sharp tooth. The antennae are kinked in both species, but far more discernible in the males.

It's interesting to compare the two individuals featured below as the first is a freshly emerged adult, which has a rather different body shape than the one photographed a bit later in the year when the abdomen has become greatly distended as a result of gorging on foliage.

The last photo shows the larvae firmly attached to an unfortunate wasp-like sawfly in a clear case of misidentify as they obviously thought it was a bee.

Updated, June 22 (v.2)