Many enemies of such bivalves as oysters and clams can be controlled by the use of heavy oils, such as orthodichlorobenzene. These oils are mixed with dry sand, or other inert carriers, to anchor them in place on shellfish beds. Effects of the treatment may be increased by incorporating other chemicals in heavy oils. The treated sand can be used to surround the shellfish beds, thus preventing the entrance of the enemies, or it may be spread over the infested areas, killing the enemies and, under certain conditions, stopping their larvae from reinvading the beds. Snails, starfish, and, in some instances, crabs can be controlled in this manner.