This is the peak season for observing the brook lamprey, Lampetra planeri, breeding in unpolluted shallow streams. Adults will be wound round each other placing fertilised eggs in stony nests built for the purpose. The brook lamprey is the smallest of the three lamprey species found in the UK, at 14 cm long, and is not migratory like its rarer, bigger cousins, the river and sea lampreys, the latter growing up to a metre.
All three types are remarkable survivors. Lamprey fossils pre-date the dinosaurs by 100m years and are more primitive than most fish in that they do not have bony skeletons but are held together by cartilage, like sharks. After breeding, they die, leaving their eggs to hatch. The larvae drift downstream to find a muddy patch where they burrow and stick their heads out, filtering edible organic matter out of the water, so cleaning the streams in which they live. After three to five years they reach maturity and metamorphose into adult lampreys, growing eyes and a suction disc with blunt teeth, but their digestive system disappears.
Unlike their larger cousins that use this sucker to fasten on to fish and chew into them, the adult brook lampreys do not eat but use these suckers and teeth to grab stones to build their nests.
