Large Amber Snails (Succinea putris) are occasionally seen with swollen and banded eye-stalks which pulsate. These have been infected by a parasitic flatworm (L.paradoxum) which uses the snail as an intermediate host to get from bird to bird. Mistaking the infected appendage for a caterpillar, birds peck off the eye-stalk or eat the whole snail. The ingested parasite larvae develop into flukes in the small intestine of the bird which later voids the fluke’s eggs wich can be eaten by another snail.
The snail is common in marsh vegetation but infected specimens have only been seen on a few occasions, notable at the Ted Ellis Trust Reserve at Wheatfen.