Insects too believe in self-medication. Monarch butterflies can cure themselves and their offspring using medicinal plants. Researchers found that certain species of milkweed, which the larvae feed on, can reduce the threat of a deadly parasite. They also found that parasite-infected female monarch butterflies prefer to lay eggs on plants that will protect their offspring from illness. This behaviour in butterflies is trans-generational. The study is one of the best evidence to date of insects using medication.