A reader in south Louisiana wrote us a question a few days ago about a black worm with a brown underside that he found in his backyard. The worm is about three or four inches (seven to ten centimeters) long, and its body is flat. The reader was wondering what type of worm he found, and if it is parasitic. The latter concern is connected to his dog, who has had issues before with worm infections. We’ll do our best to address both issues, which are of course related.