Monarch butterflies have the longest migration of any insect, traveling up to 2500 miles. Those found east of the Rocky Mountains migrate to Mexico, where they hibernate in the same oyamel fir trees used by previous generations. In the west, the butterflies travel to southern California where they overwinter in eucalyptus trees. Some of the trees can appear to be completely coated with butterflies. They travel south to avoid the cold, but they return north because the milkweed plants vital for their caterpillar’s survival is not found in their winter grounds.
Scientific & Common Names
Kingdom - Animalia
Phylum - Arthropoda
Class - Insecta
Order - Lepidoptera
Family - Nymphalidae
Genus – Dana
Species - Danaus plexippus
Common Names – Monarch Butterfly, Milkweed Butterfly
Monarchs are orange with black stripes with a wingspan up to four inches. The females have darker black stripes but the males are slightly larger. Caterpillars are just shy of three inches and they have thin stripes of alternating black, white, and yellow.
The life cycle of monarch butterflies is surprisingly complex and varies depending on the time of year the butterfly hatches. Eggs are laid on milkweed plants in April or early May and hatch after about four days into larvae, also called caterpillars. For two weeks, the caterpillar obsessively eats the milkweed and grows to its full size. Once the desired size is reached, the caterpillar attaches itself to the plant with silk and transforms into a chrysalis. The chrysalis remains in a pupa stage for ten days while the butterfly is formed. At the end of the metamorphosis, the fully formed butterfly emerges and flies away. This first generation butterfly will live from 2-6 weeks before laying eggs itself and dying. The second generation hatches in May or June and the third in July and August, each of which follows the same pattern as the first generation. The fourth and final generation for the year emerges in September and October and differs from the first three generations only in the final stage. The fourth generation does not lay eggs at that time but migrates great distances to Mexico or California, where they will live for months until it is time to move north, mate, and then lay eggs that will then become the first generation for the next year.
While the caterpillars feed exclusively on milkweed plants, the adult feed on the nectar of any flower. Due to the amounts of milkweed, a naturally toxic plant, the caterpillars feed on, monarchs become poisonous to many of their predators, including birds and mice. The bright and easily recognized colors of the monarch help to identify them as dangerous to potential predators.
Modern monarchs appeared two million years ago in the tropical region of North America. Today, they are found across both American continents, as well as Australia and Hawaii, where they have been introduced. Their scientific name, danaus plexippus, translates to "sleepy transformation".
Monarch butterflies are not currently threatened, but the loss of their overwintering grounds to development and the continued loss of areas where milkweed can be found in abundance is causing their numbers to shrink. There have also been major losses in recent years from cold snaps in Mexico.
The Monarch Butterfly: Biology and Conservation by Michelle J. Solensky and Karen S.Oberhauser
The Last Monarch Butterfly: Conserving the Monarch Butterfly in a Brave New World by Phil Schappert
Nomads of the Wind: The Journey of the Monarch Butterfly and other Wonders of the Butterfly World by Ingo Arndt(Author), Claus-Peter Lieckfeld(Author), Peter Huemer(Author)
A Field Guide to Eastern Butterflies (Peterson Field Guides) by Paul A. Opler, Roger Tory Peterson and Vichai Malikul