Animalpedia: Soldier Crabs

This is a soldier crab, most likely Mictyris longicarpus, the light blue soldier crab. They live on the sand and mudflats in Australia from Victoria to northern Queensland. They tend to come out of their temporary burrows when the tide is out to feed on organic material that they filter out of the moist sand. They seem to make a looser packed ball of sand of discarded than the sand bubbler crab.

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).