Heimlich is shown to have a gluttonous appetite and is seen eating almost all the time, especially while helping the ants construct a model bird to scare Hopper and his gang. Although brave, he still shows fear when a real bird nearly eats him. Also, when Hopper shouts at the approaching circus wagon, he frightens Heimlich who says he thinks he's going to wet himself.
Heimlich is a fat green caterpillar with a German accent who works as a clown in P.T. Flea's circus troupe. He is very gluttonous and always seems to be eating. Even during a performance, he offered to help finish one of the audience members' candy corn. The fly refused, but then it turned out that he got the candy corn anyway. He then later calls the flies "Poo-Poo Heads" when Francis is arguing with them.
At the beginning of the film, he says that he dreams of being a "beautiful butterfly." Heimlich is carried by the rhinoceros beetle, Dim, for transport. He also at one point turns gray when he sees the mural of him being killed in the battle against the grasshoppers. At the end of the film, he pops from his chrysalis, squeezes out (having only turned blue), and sprouts a pair of tiny wings, finally a butterfly, but still remains flightless (due to his obesity and because he apparently didn't stay in the cocoon long enough), and it takes the efforts of Francis, Manny, Flik, and a few other ants to get him up in the air.
He appears close-up in an outtake of the film, alongside Flik, where they express their excitement about the making of a sequel to their film, but tells Flik that the film is a sequel, but it is not for A Bug's Life, just before the scene from the film listed below occurs and they get knocked off the branch as Buzz Lightyear chops it down.
Heimlich is also present during the film: he is seen crawling on the branches just before Buzz chops down the branches.
While Buzz is looking for Woody at Al's Toy Barn, he passes toys of Heimlich and other characters from A Bug's Life.
Heimlich also appears in a McDonald's commercial for A Bug's Life, where he eats the film and Flik berates him out for ruining it. After Flick left, Heimlich licked one of his hands and after enjoying the taste, asked "Who says there's nothing good on TV?", before sucking all 4 hands at once.
Heimlich is the second Pixar character voiced by the late Joe Ranft, after Lenny.
Heimlich isn't a meetable character in theme parks, but he is a robotic character in the Pixar Play Parade in Disney California Adventure located in Los Angeles and Anaheim, California, and is part of the ride "Heimlich's Chew-Chew Train" in A Bug's Land. His theme park robots were voiced by John Ratzenberger.