Look Out for Oil Beetles in the Touraine Loire Valley

Any minute now bizarre lumbering irridescent black beetles will be appearing in woods and grasslands in the Touraine Loire Valley. These are the ranunculus munching oil beetles. They like buttercups and wood anemones, which they eat so they can accumulate their toxins. It makes the beetles themselves toxic, and their larvae, which you might spot sitting on flowers, trying to hitch a lift on a bee. Once their ride has arrived they get transported into the bee's nest, and will feed on the pollen gathered by the bees for their own larvae.

 

Violet Oil Beetle. This one was photographed a few years ago at the Moulin de Malicorne in the Courtineau Valley.

 

Nine times out of ten they will be Violet Oil Beetle Meloe violaceus (Fr. Méloé violet). I know, I counted my records. But occasionally I will see a Black Oil Beetle Meloe proscarabeus (Fr. Méloé printanier). 

 

Black Oil Beetle. They are so similar to M. violaceus I usually have to ask for expert help to confirm the species.

UPDATE: A commentor asked if we should kill oil beetles if we see them, to help the bees. My response was NO!! The presence of parasites is a good sign for the host. It means the population is sufficient to support parasites -- who are not out to kill the entire population, because that would be depriving them of their own food. Monitoring parasites can be a good way of extrapolating information about hosts. If both are in decline then that's a problem -- and that is the case with this pairing. In addition, you don't want to kill a native species going about its business. The higher the biodiversity ie the higher the number of species, the more stable the ecology is. Everything is linked, and specialist species like the oil beetles are the keys to a well functioning natural system.