A profound joy to see these wonderful creatures. Five European Brook Lampreys - Lampetra planeri. They have a fascinating life cycle. The blind hatchlings float down stream and embed themselves in burrows in silt where they spend about three to seven years maturing, filtering organic material for food. When ready, they metamorphose into sighted adults and emerge from their burrows. This happens in the autumn. From then till early spring they live a secretive life, swimming upstream by night and hiding under stones by day. Once they've reached a suitable gravel spawning ground, in small groups they build a nest - a shallow depression in the stream bed. They build the nest by moving stones, lifting them with their round sucker-like mouths. They are able to move stones twice their body weight. Spawning happens in daylight in March or April, once the water temperature reaches about 10C. The females attach themselves to stones with their suckers and the males squirm vigorously, releasing sperm. Females release their eggs in a cloud which attach to stones in the nest, hatching within the month. Each female lays about 1,500 eggs. After spawning the lampreys die. Adult Brook Lampreys are unable to feed so they gradually loose weight during their journey upstream.