What’s the difference between the Violet and Black Oil Beetles?

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The identification of the two most commonly seen British oil beetles is something we’ve been trying to get to terms with in recent days as part of Bug Life’s oil beetle survey, just as we did last year – see Big black beetles: Black Oil Beetle.

Despite the excellent Bug Life identification guide designed to help recorders we haven’t found it as easy as we would have expected when trying to identify these large black beetles in the field. The Violet Oil Beetle (latin name Meloe violaceus, above left) and Black Oil Beetle (latin name Meloe proscarabaeus, above right) are almost identical, rarely seem to keep still, and, when seen in bright sunlight, have the key identifying features of their thoraxes often obscured in either deep shadow or glare.

As ever, when uncertain on species identification we have resorted to photographing and studying the images later on the computer.

The identation on the base of the thorax of the Violet Oil Beetle (detail above left) can then be compared with the straight base of the Black Oil Beetle (detail above right) and things become a little bit clearer!

Even so, despite using computer image enhancements, the sharp tooth like notch below the base line is still not obvious.

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