Arcitalitrus dorrieni (Hunt, 1925)

The landhopper or woodhopper is an amphipod crustacean, and differs from isopods (e.g. woodice and waterlice) in having the body flattened from side to side (rather than top to bottom). It readily jumps into the air when disturbed (reminiscent of a very large flea - about 1 cm long!). It is the only amphipod that occurs inland on 'dry' (damp) ground and is characteristically dark (almost black) in colour.

Arcitalitrus dorrieni was once considered to be synonymous with A. sylvaticus, Haswell, 1879, but subsequently these have been shown to be distinct species. Unfortunately, the name A. sylvaticus has been used in the past and this has resulted in the confusion that two species of Arcitalitrus occur in Britain and Ireland.  In fact, only one, A. dorrieni, has been recorded (Gregory, 2016).

Confusion is most likely with the introduced semi-terrestial amphipod Cryptorchestia garbinii Ruffo, Tarocco & Latella, 2014 (recently split from C. cavimana (Heller, 1865)), which is less darkly pigmented and although able to penetrate far inland it rarely strays far from water margins. The two species are described and figured by Gregory (2016). Other British 'terrestrial' amphipods rarely occur far above the high tide mark on the coast and are often pale orange in colour (most are intertidal). 

Three additional species of terrestrial landhopper have been recorded from inside heated tropical glasshouses. These are Brevitalitrus hortulanus Calman, 1912, Talitroides alluaudi (Chevreux, 1896) and T. topitotum (Burt, 1934).