It is a known fact that garter snakes, just like any other type of snake, are carnivorous in nature. So what exactly do garter snakes eat? Garter snakes will eat close to everything that they are able to overpower. Cold blooded animals such as frogs, toads or earthworms are some of what garter snakes eat. They also consume slugs, leeches, lizards, insects such as spiders, rodents, amphibians, insects and birds.