Arcitalitrus dorrieni (Amphipoda: Talitridae) has been found in a compost heap in Cirencester. While digging post holes to replace a storm-damaged fence in Cirencester last week, I had to move some old compost out of the way. As I did so, a small being hopped around over the surface. First thoughts were that it was a large springtail but second thoughts were it was too large and too shiny, and it behaved like the sandhoppers you find on beaches. Investigation proved it to be a shrimp about 8mm long, very dark brown in colour and glossy. After the initial hopping around it played dead before trying to crawl back into the substrate. With one exception, all shrimps in this country are found in water courses and lakes. The exception is A. dorrieni, a species described as new to science in 1924 from the Scilly Isles. After some years it was found on the Cornish mainland where it has spread slowly through South Devon and part of Dorset. Outlier populations were subsequently discovered in Bristol and Kew. More recently it has been found in South Wales and Inverewe gardens in Northwest Scotland and a very few other sites.
It is now known to originate from Australia and was most likely imported with plants from that region. This particular compost heap has not been disturbed for several years (being a student house) and, from the numbers seen, the population appears to be well established. In the Southwest and Inverewe the species is found in woodland leaf litter.
English names for this species are Wood Hopper, Land Hopper and Lawn Shrimp. Not being a freshwater species it has been adopted by the British Myriapod and Isopod Group as an “honorary woodlouse” and distribution records end up with them. As county recorder for the Group I would be interested in any records or specimens that people think might be this species.