Milkweed and monarchs
Monarch butterflies are specialists which puts them at a certain risk. Their larva can only eat milkweed plants – with habitat destruction and the use of certain herbicides on large acreages of crops, milkweed plants, once common across the country, have vastly diminished. The plants produce toxic compounds, monarch larva, immune to these poisons, eat these plants and then retain the toxins in their bodies which pass to the butterflies, too. Birds have learned that monarchs have a horrible taste, if a young bird eats a monarch, it will vomit and will have learned an important lesson and avoid monarchs from then on. There are two birds, residents year-round or part time in Mexico, the black-backed orioles and black-headed grosbeaks that eat only certain parts of the monarch body and avoid the concentrations of toxins.