It is a capable swimmer and feeds in open water in the north-east Atlantic Ocean and western Mediterranean Sea.

[1] Polybius is found in the north-east Atlantic Ocean from the British Isles to Morocco, and in the western Mediterranean Sea.

[2] Polybius henslowii is a capable swimmer, and can be found swimming near the ocean surface, where it feeds on a mixture of squid, fish, and other crustaceans, including specimens of the same species.

[6] When they swim inshore, along the coastal upwelling areas of Galicia (NW Spain), they rely more on benthic prey, such as polychaetes and detritus [6] and are influenced by terrestrial organic matter coming from the rivers.

[7] In Galicia (NW Spain), P. henslowii is an important food source for the yellow-legged gull, Larus michahellis.