Most butterflies will use more than one plant species as a host for their larvae. Monarch butterflies will obtain nectar from a variety of flowers, but lay eggs solely on milkweed leaves.
An interesting fact about monarchs is that the caterpillars eat the toxic leaves of milkweeds and store the toxin in their bodies, which makes them poisonous to predators. They advertise their toxicity through their bright coloring.
On the other hand, black swallowtail caterpillars feed on non-toxic hosts like parsley, dill, and fennel. But, the adult swallowtail butterfly fakes toxicity by mimicking the coloring of the pipevine swallowtail, which is poisonous.
The first three to four generations of Monarchs hatched in spring and summer live about one month each, but the last generation of Monarchs east of the Rocky Mountains – those born around September or October – lives 6-9 months. This is the generation that migrates to Mexico, returning to the United States in early spring to mate, lay their eggs and die. In their lifetime, this last generation may travel up to 3000 miles.