Its name comes from its tendancy to form large groups (hundreds) of crabs which then march down the beach. I’ve heard tell that the larger crabs ‘direct’ the movement (i.e. smaller crabs follow them) earning them the nickname of general crabs, but I have yet to find some verification of this. When disturbed, the crabs corkscrew into the sand on their side.
Young soldier crab
'General' soldier crab
Soldier crabs have an interesting physiology, their gill chamber is modified to work in air and water. The gill chamber is divided into two sections, one which circulateds water over gills, and the other section is a thicker lining of respitory tissue penitrated by thin tubes ending in a thin layer of tissue, much like the insect trachiole system in function (Maitland and Maitland, 1992).