Oil beetles are another one of those species that not everyone is comfortable with due to their interesting life cycle which we’ll come to.
They belong to the genus Meloe which is a large group with
some 35 species of Oil beetle in Europe and 15 in France
although I’m not sure how rare some of them may be and they are also somewhat
understudied according to OPIE. Certainly the commonest are the Black Oil
Beetle Meloe proscarabaeus and the
one I find at our place the Violet Oil Beetles, Meloe violaceus, and we sure have a lot of
them, so many that it’s hard not to tread on them when walking among the trees
where the Lesser celandines are flowering at the moment.
Click images to enlarge
Below: Newly emerged female before putting on weight.
Below: Female having put on weight.
Below: Recently emerged male with pronounced kinked antennae.
Below: Another male, again showing pronounced kinked antennae.
They are a flightless beetle without functional wings, and
shortened elytra, (modified, hardened front wings), and they have a very
interesting life cycle as mentioned.
Soon after emergence in March / April the adult beetles mate after first
putting on some weight. With both the Violet and Black Oil Beetle the males have
kinked antennae which they use to hang on to the females antennae with during courtship.
Once coupled they remain attached with
the male being dragged around for an hour or more. The female then lays her
eggs in a small hollow she digs in the soil and when these hatch the larvae,
(called triungulins as they have 3 hooks on each foot), climb up the vegetation
and wait on a flower head for a passing bee to settle to which they attach
themselves. Very few survive but those that do and manage to hitch a ride are
taken back to the solitary bees’ nest where they consume the bees’ eggs and the
nutrition that has been put there. They then pupate and emerge the following
year.
Below: Violet Oil Beetles coupled.
Below: Violet Oil Beetle eating Celandine.
They are classified as cleptoparasites and not actually parasites.
“”Kleptoparasitism or cleptoparasitism (literally,
parasitism by theft) is a form of feeding in which one animal takes prey or
other food from another that has caught, collected, or otherwise prepared the
food, including stored food (as in the case of cuckoo bees, which lay their
eggs on the pollen masses made by other bees). The term is also used to
describe the stealing of nest material or other inanimate objects from one
animal by another.” SOURCE
Despite this behaviour which some dislike they are a good
indicator of the level of solitary bee activity where they are located for
without them they can’t exist.
As can be seen in the photo Oil beetles often attract small midges which feed on the oil produced by the beetle but do it no harm.
Rugged Oil Beetle Meloe
rugosus, Mediterranean Oil
Beetle Meloe mediterraneus and the Short-necked
Oil beetle Meloe brevicollis are some other well known but scarcer
French Oil Beetles.
