Beetle Mania

The other day I was waiting for clients at la Maison des abeilles/Happyculteurs on the outskirts of Champigny sur Veude. Next to the picnic table where I was sitting is a mature Horse Chestnut, no doubt planted to provide shade back in the days when this site was the railway station. 

I spotted a beetle at the base of the trunk, a very striking red and metallic blue creature, and quite a size (more than 20 mm). I could see at a glance that it was a longhorn (Fr. capricorn) beetle of some sort, but a species I had never seen before. It was struggling to climb up the tree as it had lost its foot and tibia on one back leg. I was able to take lots of photos with my phone (but I didn't have my camera with me).

Once home I identified it as Rhamnusium bicolor. It doesn't have an English name, but its French name is le Rhagie ermite. There was a flurry of excitement amongst my coleopterist friends, who were not at all jealous...ahem...

The French National Natural History Museum page for the species tells me that this is a widespread but uncommon species, favouring old deciduous trees such as Horse Chestnut, Poplar and Beech in damp environments, often in towns. So where I found it was exactly its preferred habitat. Most observations are in May or June.

The head, thorax (pronotum), legs and base of the antennae are brick red. The elytrae (wing cases) are blue, but in some individuals, can also be brick red. There are no lookalike species, so it is easy to identify. 

The larvae develop in cavities in old deciduous trees. They eat the damp decaying wood that lines the cavities or damaged parts of the tree. They slice the wood in very characteristic long thick strips of fibre. The adult beetle is rarely observed, except occasionally at the opening of a sunlight cavity. Their life cycle, from larva to adult takes one to three years.

The species is present throughout Europe, to the Urals. In France it is widely distributed but rarely seen, because it tends to be active at dusk or at night. It is found more frequently in parks, tree-lined allées and gardens than in the forests. It is assumed to be dwindling in population, linked to the increasing rarity of trees with cavities.