Police arrested Michel Rouyer after they discovered 12 cannabis plants and about 5kg (11lb) of the drug during a visit to his home after a theft.
Mr Rouyer said there was “no better worming substance” for ducks and that his flock was in excellent health.
A police spokesman said it was the first time they had heard such a claim.
Mr Rouyer, who lives in the village of Gripperie-Saint-Symphorien on France’s Atlantic coast, did also admit to smoking some of the marijuana.
Taken from the BBC