Freshwater Shrimp - Gammarus pulex/fossarum agg.

A greyish or brownish freshwater crustacean growing to 21 mm but usually less. Not a true shrimp (actually an Amphipod), but sometimes referred to as the Freshwater Shrimp or River Shrimp.

Gammarus fossarum was only discovered in the UK in 2017 so earlier publications refer to Gammarus pulex. Gammarus pulex/fossarum agg. is in fact a species complex of many cryptic species, distinguishable only by DNA analysis. 

Freshwater. They prefer flowing water but have also been found in ponds.

All year round.

The life cycle of Gammarus pulex is complex. Males grab and hold females before deciding which one is likely to produce lots of eggs. Then the male carries his chosen female for several weeks until she sheds her skin and the male can mate with her. He then lets her go and she carries the developing young in a brooding pouch. After about a month, the young shrimps swim out of the brood pouch, and a few months later they can breed themselves. As females can produce up to 50 young each month, the population soon grows.

Common and widespread in Britain.

Common in Leicestershire and Rutland.