Haemopis sanguisuga or Horse Leech can grow up to 10 cm long. Although this specimen is much smaller. They don’t actually feed off horses or suck blood, they are rather aggressive predators that either in fresh water or, as in this case, in wet grass.

Horse leeches have five pairs of eyes and three sets of teeth. They prey on invertebrates and small amphibians and fish. After photographing, I carefully put it back into the water. They are relatively common in Europe.

This specimen was caught in County Roscommon.

More information can be found on wikipedia:
https://en.wikipedia.org/wiki/Haemopis_sanguisuga