As winter approaches, it becomes harder to find a good range of interesting invertebrates/plants/other things to blog about, so to stop this from turning into ‘slug of the week’ I’ll sometimes blog about things that are more likely to be found in the summer.
So, the species this week is Thanasimus formicarius, A.K.A the Ant Beetle, or the European Red-bellied Clerid. This unusual beetle is given the name ‘Ant Beetle’ as the way it moves, and its colouration mimics an Ant. Here is the beetle:
I said that the Ant Beetle mimics an ant, but I tell I lie. Its colouration is very similar to that of the Velvet Ant (Mutilla europaea), which despite its name, isn’t an ant at all, but a solitary wasp. The Velvet Ant can be found in similar areas to the Ant Beetle, and is noted for its painful sting, so is a fairly useful species to be mimicking! Here’s the Velvet Ant for comparison:
The Ant Beetle spends two years as a larva, before overwintering at the base of a tree, usually a Pine tree. The Beetle then emerges in Spring and seeks out fallen Pine trees and log piles, where it waits for its prey (Bark Beetles) to arrive. Bark Beetles are fairly well armoured, so Thanasimus formicarius uses its strong jaws to bite the legs off, and immobilise its prey. It can then take its time about breaking open the Bark Beetle, targeting weaker areas between the head and pronotum (thorax), and between the pronotum and elytra (abdomen).
I’ve only seen the Ant Beetle twice in several years digging around in log piles! Once was under the bark of a log in Monks Wood, Huntingdonshire, and once was on a coastal heathland in Suffolk, where the beetle walked right past me as I was having my lunch. It is best found by checking Pine stumps, logs and fallen trees, but as with most things, a good dose of luck will help!
T.formicarius is widespread but fairly uncommon in Southern and Eastern England, and has also been found in Northern Scotland. See distribution map here:
One similar species, T.femoralis has been recorded only from Northern Scotland, but appears to be very rare. It can be distinguished by having reddish femora and tibiae (black in T.formicarius). I think that T.femoralis is also smaller (about 6mm), whereas T.formicarius is larger (about 10mm), but I’m not certain!
The Ant Beetle is one of my favourite beetles, so I hope to see it again soon! (And hopefully in Cornwall, as it’ll be a new county record!).