On the 24th of September this year we were down by the beach when my five year old daughter Iris came up from the sand clutching something in her hand. It looked like a curled up worm with a flattened body, and I couldn't recognise it as one of the creatures normally found on the shore.
Placing it in a paper cup of sea water, it stretched out and fixed one end of its body to the side of the cup with a sucker. It was clearly a leech. After taking a few photographs for identification purposes, the leech was placed in a pool under some rocks so it could crawl away from predatory seagulls until the tide came in.
At home, despite consulting numerous identification guides I couldn't find a match. Marine leeches prey on fish and are usually found attached to them when they are caught. It didn't look like a marine leech.
The photos were posted on the Wild About Britain water life forum and It's fair to say they caused much consternation. Someone even suggested that it might be a juvenile hagfish (a jawless fish similar to a lamprey). Of course the sucker and highly extendable body precluded this. It was certainly a member of the Hirudinea, the leech family.
There are lots of pipes that drain water from the cliffs onto the beach just below where our beach hut is situated, and it struck me that this might not be a marine species at all, but a fresh water or terrestrial creature that had been washed out of one of these ducts. Indeed the most likely ID turned out to be the rare terrestrial leech Trocheta subviridis.
Quite capable of living in water with a high level of pollution from sewerage, the leech was undoubtedly living in one of the drainage pipes and was flushed out onto the sand. Trocheta subviridis is a predator of earthworms and leaves the water to hunt. There are reports of it crawling up plugholes into people's sinks and it is sometimes dug up in gardens. Because of its lifestyle it is sometimes called the Amphibious Leech.
In the journal Parasitology, vol. III, p. 182 ther is an account of one being found on an allotment in 1922.
In April of this year a specimen was sent to the Agricultural Department, Armstrong College, by Mr S. Giles of South Shields, along with a note explaining that it had been found “down in the first spit of the soil” in one of a group of allotments there. It was obviously a specimen of a leech, but the specimen was submitted later, to Mr John Ritchie, the Museum, Perth, who kindly identified the species as Trocheta subviridis, and who mentioned that "this gives so far as I am aware, a more northern habitat than hitherto recorded".
Definitive identification of leeches needs to be carried out when the creature is still alive and its body relatively transparent. Also a handlens is essential to count eye spots. This has been a lesson to me. Now whenever I go to the beach, I always take a magnifying glass of some sort. You never know what you might find.