Some Aspects of the Behaviour of the Soldier Crab, Mictyris longicarpus

THE CRAB, Mictyris longicarpus Latreille 1806, belongs to the brachyuran family Micryridae Dana 1856. According to McNeill (1926) the species ranges northward from southern New South Wales and from Perth, Western Australia, to New Caledonia in the east, to Singapore in the north, and to the Bay of Bengal in the west. In Australia Mictyris is known as the "soldier crab." This appellation is appropriate in view of the habits of the genus . Immense numbers of M. longicarpus (Figs. 1 and 2 ) congregate in dense masses and wander over tidal flats in apparent formation. Their activities exert a particular fascination not only because of these huge "armies," but also because soldier crabs walk forward and not sideways, as do most crabs. Several authors have commented on the habit of Mictyris of wandering in armies (MeNeill, 1926; Lazarus, 1945; Balss, 1955-56; AItevogr, 1957; Schone, 1961; Stephenson, 1961). However, little is known of the organisation of this behaviour and I decided to study M. longi carpus with a view to describing it. Because of the immediate flight and burrowing reactions of soldier crabs to the disturbing influence of observers , the pattern of behaviour to be described has been previously overlooked.