[2] Examination of the gut contents of M. longicarpus showed that the crabs mostly feed on detritus, and any small organisms in the sand, such as diatoms, gastropod eggs, or nematodes.

[4] Predators of adults include Threskiornis spinicollis (straw-necked ibis), Todiramphus sordidus (Torresian kingfisher), Egretta alba (great egret), Tetractenos hamiltoni (common toadfish) and Metopograpsus messor (a grapsid crab).

[4] The first sign that a crab may emerge is the development of "hummocks" which appear on the surface of the sand and increase in size over a period of 10–30 minutes.

Feeding comprises raising scoops of sand to the mouthparts, with inedible material accumulating at the base of the third maxillipeds, and drop off the crabs as round pellets.

[4] The armies are generally composed solely of males, with the largest individuals at the front, probably because their longer legs mean they walk faster.

[4] Eventually, the army breaks up and the individual crabs travel up the shore, and dig themselves into the sand in a unique corkscrew motion.

[4] Michael Tweedie considered crabs of the genera Mictyris and Scopimera to show types of behaviour also seen in human society.