The warm weather over the past week has made it easy to find this Romney Marsh speciality by splash sampling. You stand in a ditch and splash for fifteen minutes and after a few minutes the medicinal leeches come looking for a blood meal, swimming through the water towards the disturbance. This large specimen, placed over a bag because I did not want any accidental bites while I was netting the ditches, shows the size these animals can reach and their characteristic green colouring with a pair of red lines along the back.
This was part of a sample of leeches that were having the diameter of their posterior sucker measured to get an idea of the relative proportion of adult and young leeches. The trouble with the adults is that they regularly contract and stretch, so a measurement of body length is not useful. Similarly weight can very dependent on whether or not they have had a blood meal (so many selfish naturalists wearing plastic bags this month - takes the fun out of finding a human!)
The photograph above shows a number of sampled leeches showing how flexible they are, with the posterior sucker clearly visible in some. It also shows how variable their colour can look. The same animal can look green under some light conditions, very dark and almost black in others, and at night under torchlight, they show a lot of yellow colouration as they swim through the water.