'Aithníonn ciaróg ciaróg eile' is a well-known seanfhocal or traditional old-saying in Irish. A 'ciaróg' is, of course, the Irish for a beetle so the phrase literally means 'a beetle recognizes another beetle'. However, literal word-by-word translation makes no sense in any language as it fails to capture the intended meaning of the phrase and, in this case, its dismissive implication.
The meaning of the Irish phrase 'Aithníonn ciaróg ciaróg eile' can best be equated to the English phrases: 'It takes one to know one', 'Birds of a feather flock together' or 'Like sees like'.
While the word 'ciaróg' is used in a generic sense to mean any beetle, it is often used to refer specifically to the insect otherwise known as the 'Common Black Ground Beetle'. A more user-friendly name is 'clock' or to distinguish it from the timepiece, the 'black clock'.
Whether you know it as a clock, a black clock or a ciaróg, the Common Black Ground Beetle is one of the most abundant and widespread members of a very large family of insects known as ground beetles or carabids. It is very common in gardens and on arable land. It is not averse to coming indoors and will freely enter houses in summer if the opportunity arises. It is, of course, totally harmless.
It is a handsome creature with a jet black, shiny, metallic body divided into the three parts typical of most insects: head, thorax or chest-part, and abdomen. The head bears a pair of large, bulging eyes and long thin antennae that twitch in the air picking up scents, so they are smellers rather than feelers.
Like most insects, it has six legs arising from the thorax. These legs are normally black in colour but there is a variety called 'concinnus' that has dark wine-red legs rather than the more usual black.
It has four wings. The hind wings are like the wings of a wasp, but the fore wings are hardened wing cases that cover the hind wings when folded away out of use. These glossy black wing cases have deep longitudinal grooves running along them and are fused together so the beetle is not capable of flight.
The Common Black Ground Beetle, clock, black clock or ciaróg is largely predatory. It hunts outdoors for ground-living invertebrates like caterpillars and slugs. If meat is unavailable it will readily feed on plant material as a fall-back.