Rats, like people, are omnivorous which means they eat both plants and animals. Wild rats eat nuts, seeds, grains, vegetables, fruits, insects, worms, eggs, dead animals, and even frogs, fish, reptiles, birds and mammals that they catch and kill. This means they are partially predatory and have a high requirement for some nutrients that are most abundant from animal sources. This predatory nature is why rats are so smart! Rats do not need a salt lick. They get all the salt they need from their diet. Salt licks are only needed by strict herbivores.