Worms from the depths…

Last weekend, on the way back from a great stay at Portland Bird Observatory, I met Tony Davis and Josie Hewitt in a small car park in the New Forest. Our aim was to find as many rare plants as possible and we did well, finding really uncommon species such as Yellow Centaury, Pillwort and the delightfully named Duck-potato. Below are a few photos of the plants we managed to record.

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Autumn Lady’s-tresses

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Pillwort, this is actually a fern and reproduces using spores!

Despite seeing over 30 new species for my pan-species list that day my highlight was actually an annelid worm! I don’t often look at annelid worms (which are mostly earthworms) as they are not the most exciting creatures in my opinion and I find them very tricky to identify. However the species I added was far from boring!

To find this species, we stood in a pond.

We didn’t have to do anything else, just stand in the pond and wiggle our feet. It wasn’t long before I spotted a long dark creature swimming towards me like an eel on its side. It twisted through the water and came right up to my boot before swimming off. Then Josie spotted another at my heel. There were several of them, twisting through the water weeds with elegant wavelike movements.

This part of the New Forest is excellent for this species of annelid worm, the Medicinal Leech. This is due to the number of ponies providing the leeches with lots of food! Many leeches are terrestrial, however some, like this species, prefer to inhabit freshwater and are adept at swimming. The Medicinal Leech is often mistaken for the Horse Leech, which the leeches in this pond were at first thought to be. Although they appear very similar in appearance, they have very different prey preferences. Despite the name, Horse Leeches can’t penetrate the tough skin on mammals and therefore cannot feed upon their blood. Instead they choose to eat much smaller prey, such as snails and earthworms, both in the water and out. Medicinal Leeches are able to bite tough skin and their main food sources are cattle and horses. However, they also feed on frogs and sometimes even humans!

Unfortunately, these fascinating invertebrates are one of the few I know to have an IUCN designation worse than Least Concern. Most are Not Evaluated or Data Deficient and the species with enough research to provide details on the fluctuations and size of populations are often not too rare. They are classified as Near Threatened despite the population trend – among other things – being unknown. Their main threats are local collection for medicinal use; loss of habitat; and decline in one of their main prey items, frogs.

Below are a few photos I was able to take of the leeches that swam towards us:

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