The Soldier Crab lives in sandy estuaries and mangroves, and occurs in massive groups that seem to emerge from nowhere all at the same time. A small army of Soldier Crabs inhabits the calm waters of the Spit (Doug Jennings Park) on the Gold Coast - pictured below.
Soldier crabs will comb the sandy intertidal zones scooping up this debris with their front claws and eating it. The crabs will then deposit the waste sand that is left over in compacted balls called pseudofaece. The photo above shows a small 'army' of Soldier Crabs moving across the beach, also seen is the pebbling effect of the beach being their compacted waste.
It is thought that their spontaneous arrival is triggered by the falling tide. If disturbed, they burrow into the sand with a corkscrew motion, disappearing as quickly as they arrived. In the photo below one little fella is just poking his head out for a look behind his mate.
The Soldier Crabs are also the only crabs that can walk forwards rather than sideways.