The monarch (Danaus plexippus) uses two methods of self-defence – warning colouration and toxicity. The monarch butterfly’s bright colours are warning signs for vertebrates to stay away. Scientists call this aposematic colouration. Just as we humans learn that high-visibility vests and orange cones mean danger, birds and other predators learn that brightly coloured monarchs are harmful to eat. This is due to the monarch’s other method of self-defence – toxicity.