Ram’s-horn Snail ‘new’ to Highland Scotland found at Stoer
Late in the summer of 2020, Bill and Val Badger made a small pond (photo 1) in their garden at Stoer (NC0328). It was furnished with a variety of aquatic plants, some obtained locally, others from on-line suppliers.
On 13th April 2021, we were admiring the busy microcosm it had already become, with water mites, lesser water boatmen and small water beetles dashing about. Making tracks, at a more decorous speed, through algae coating its liner were water snails. Some were the widespread wandering pond snail Lymnaea peregra, others the flat spirals of ram’s-horn snails (Planorbidae), which are not so familiar. From past experience, the latter are quite challenging to identify, so we borrowed one, about 12mm in diameter, for Gwen to photograph close-up (photos 2-4).
We sent her pictures to Dr Adrian Sumner, our conchological guru down in East Lothian. The choice was between two closely-related species, the margined ram’s-horn Planorbis planorbis and the keeled ram’s-horn Planorbis carinatus, which are separated by subtle differences in the relative size of the whorls, shape of the opening and location and sharpness of the margin or keel.
Adrian wasn’t quite certain of their identity from the pictures and asked to see a couple of live specimens. These were duly collected on 20th May and posted to him, wrapped in damp kitchen paper inside a plastic tube (and later returned, for repatriation). It was probably just as well the Post Office did not ask for any qualification of the description ‘natural history specimens’ for the contents of the small parcel.
He has now confirmed them as keeled ram’s-horn, which was, happily, our provisional diagnosis. There are no records of this species on NBN anywhere in the Highlands, the northernmost being from Blair Castle in Perthshire (NN8666), where it was found by Mrs Beryl Rands (an old friend of Ian’s) back in August 1971. The margined ram’s-horn is almost as rare this far north, but some were found in a garden pond at Drumbeg (NC1232) in February 2014 (Evans, 2015).
Both these species, and others, appear to be spread accidentally in aquatic plants acquired for garden ponds, and may be more widespread than hitherto suspected.
Ian M. Evans and Gwen Richards
Reference Evans, I.M., 2015. Sutherland ponds: some unexpected discoveries during 2014. The Highland Naturalist 11, 21-23.