Blind beetle found at Nedd
Just after 8 a.m. on Friday 11th August 2023, I went out down my garden at Nedd (NC1331) to read my weather instruments, which are in a box at the top of a fence post. Whilst I was checking them a small brown beetle sprang on to my hand and started running around it. It looked unfamiliar (as do many small brown beetles), so I closed my fist on it, got it back to the house and transferred it to a container.
I showed the beetle to Stephen Moran at the Field Club meeting at Little Assynt two days later, but he was unable to put a name to it without closer examination (it is only 2mm long).
On the Monday I set it, had a closer look under a low-power microscope and started thinking about identifying it. It is quite flat, the last five joints of its antennae are slightly enlarged, its tarsi are conventionally 5-jointed, and the thorax has flared outer back corners, but the really distinctive feature is the lack of any eyes (photo).
Since there are legions of small brown beetles and I could not remember any blind ones, I had a quick flip through a copy of an old favourite amongst my insect books, A Field Guide in Colour to Beetles by K.W. Harde (1984), the English edition of a beautifully-illustrated German work. And there, on pp. 126-7, was a possible candidate, Leptinus testaceus. I was able to confirm its identity from on-line descriptions and photographs. It has acquired the name of mouse-nest beetle, but this underplays its capabilities (see below).
Background information
Harde’s decription reads ‘The tiny, pale beetles lack both eyes and wings. L. testaceus is not rare, but it is hard to catch, since it lives in the nests of small mammals (chiefly mice and voles) and in caves, in bat excrement.’ The only other close British relative is the Beaver Beetle Platyphyllus castoris ‘the strangest of all beetles’, which lives in the fur of beavers, where it feeds on mites parasitic on them. It has now been found on those re-introduced from Europe.
A fascinating account of the natural history of Leptinus testaceus is contained in a substantial paper by one Orlando Park of Chicago, published as far back as 1929 in an American journal Psyche and available on line. He states that it is also found in the nests of social Hymenoptera, such as bees, wasps and ants, where it lives an ‘opportunistic life style’, probably feeding at times on pollen and honey, otherwise on whatever it can pick up. Ants apparently ignore it.
Quite where my specimen had come from (although there are plenty of small rodents in my garden) and what it was doing out in broad daylight some distance off the ground, running around at speed, despite its lack of eyes, I have no idea.
Other records
NBN maps over 100 records of this beetle, but only one is from Scotland, from near Largo in Fife (NO40L), where it was observed or collected on 12th January 1994, but with no further details available. So, this is certainly a first for the Scottish Highlands. Coincidentally, one of the English records may well be of an individual found on a wood mouse live-trapped by a friend and I during small mammal research at a site in the Charnwood Forest, Leicestershire in the early 1960s.
Thanks to David Haines for his excellent close-up of the blind beetle found at Nedd.
Ian M. Evans