In the Order Decapoda four families of Macrura, one of Anomura, and seven of Brachyura include semi-terrestrial or terrestrial representatives, primarily tropical and subtropical in distribution.

Observations have been made largely on brachyurans. In these forms mating takes place on land, and courtship involves mainly visual and acoustic signals rather than chemical and tactile ones. During copulation the female is often hard rather than soft and may assume a position above the male rather than beneath him, as in many marine forms. Eggs are carried by the female on land. Larval development takes place either in sea water or, in the case of some fresh-water crayfishes and crabs, entirely within the egg.

Extremes of temperature are met primarily by acclimation, transpiration, or escape (immersion, burrowing). During transpiration body temperature is lowered by a few degrees but water is lost. In some species water can be replenished by uptake from a moist substratum and stored within the pericardial sacs.

Ionic regulation occurs largely through antennal glands, gills, and gut and helps to move water from exterior into hemolymph and from hemolymph into gut and its diverticula. In Gecarcinus lateralis at ecdysis, large amounts of water move from hemolymph into gut, this process being controlled by a hormone from the thoracic ganglionic mass.