[2] This is both a defense mechanism and a predatory advantage, as unsuspecting fish will hide in seaweed beds from nearby predators.

[4] Both the carapace and pereiopods of this species are greyish to yellowish or reddish-brown in colour, with some specimens showing white markings.

[2] Decorator crabs such as the Macropodia rostrata will use the algae covering their limbs as camouflage and an emergency food source.

[7] When startled, spider crabs will wave their pincers over their heads, which is their main defense against predators such as gulls and shorebirds.

[2] Although not common, large fish and sharks will prey on spider crabs, but are often dissuaded due to their hard shells.

[citation needed] Although it cannot be genetically determined what dictates minimum and maximum post-puberty sizes of Macropodia rostrata, scientists believe it is the result of varied ecological histories.

[citation needed] M. rostrata was first described by Carl Linnaeus in his 1761 work Fauna Suecica, under the name Cancer rostratus.