The Inspector's adversary was called "Spider" Pierre, but he only had six appendages (four arms, two legs). If he were really spider-like, he would have six arms.
The inspector ends up in jail over Deux-Deux's child's play money, but he never officially spent any of it. It was all taken by Spider Pierre.
The thief picks the inspector's back pocket but---when he goes to pay the barman---the inspector only checks his front pocket and his inner jacket pocket. He never once reaches for his back pocket, where he had put his wallet.