Alternatively, many other amphibia have toxic skin, which is harmful to predators. These are poisonous to eat. This is an important defence against predation. Connected to this is the use of warning colouration. They may be in vivid colours of red, black, and yellow. Research into the rough-skinned newt and the garter snake shows this is a typical case of co-evolution. Where they live in the same area, the newts get more poisonous, and the snakes develop more resistance to the poison.