Sunday, September 15, 2013
A "lousy watchman"
We found this magnificent Dor beetle Geotrupes stercorarius when we were helping to clear an overgrown garden at Winlaton Mill near Blaydon yesterday.
The armour on these lumbering insects is incredible - just look at that thick plate on the forehead and between the eyes, and those serrated edges to the legs; they're built like a battleship. Those clubbed antennae are unusual too.
When we picked it up we noticed that there seemed to be something unusual going on at its rear end and tipping it on its back revealed the cause....
..... a dense cluster of parasitic mites under its tail. Most dor beetles seem to be infested with these, giving them an alternative colloquial name of the 'lousy watchman' - presumably because that are often found after dark near lights - like night watchmen.
Blue iridescence is a feature of the underside of these beetles.
Turning it on its back also induced it to open its wings ...
..... as well as exposing its tormentors. Despite its armour it has no real defence against the mites, which attach to the softer articulating tissue between the plates of its exoskeleton. Here it's trying, unsuccessfully, to dislodge them with weak movements of its hind leg.
Dor beetles breed in chambers under cow or horse dung, dragging the dung into their burrows to feed their grubs.
It quickly righted itself and them rampaged across a gardening glove, looking mighty annoyed. The aerofoil profile of its extended elytra, that are held rigid in flight while the wings beat under them, is nicely displayed in this photo (double click for a larger image).
It looked like it might fly but never quite managed take-off, folding its wings under its elytra instead.
There's a fine picture of a dor beetle in flight on the ARKive web site - click here
For more pictures of animals infested with mites, click here , here and here .