Big fleas have little fleas upon their back to bite them, and little fleas have lesser fleas, and so ad infinitum. meaning

HOME PROVERBS

prey

Big fleas have little fleas upon their back to bite them, and little fleas have lesser fleas, and so ad infinitum.

means that:
Everyone is preyed upon by someone, who in turn has someone preying on him or her, and so on.