Happy as a clam

So I was thinking about Scylla and Charybdis today at work, and it occurred to me: going by her feeding habits, Charybdis is probably just a real big bivalve.

Picture that. A ship-eating geoduck bigger than Manhattan Island, just buried there under the straits and happily syphoning away, no fear in the world aside from Zeus' own trowel and clambucket.

How much butter would that even take, exactly?