Synonyms and other taxonomic changes
Danaus plexippus (Linnaeus, 1758)
Papilio plexippus Linnaeus 1758
Distinctive, but compare Viceroy, which has a dark line across hindwing and is smaller. See here:
Monarch often shows distinctive gliding flight with a dihedral (V).
Males have scent-scale patches on hindwings, prominent when wings are open, and just possible to see when wings are folded.
Much of temperate North America into tropics and much of South America. Also some islands in Pacific, Australia (introduced?). Highly migratory.
Open areas with flowers, hostplants
March through fall in eastern US. All year in tropics.
Adults take nectar from a variety of flowers.
The caterpillars feed on plants in the Milkweed family (Asclepiadaceae [or Apocynaceae in part]), primarily Milkweeds (Asclepias), but also other genera including Calotropis, Cynanchum, Gonolobus, Sarcostemma, etc.
The adults make mass migrations from August-October, flying to hibernate along the California coast and in central Mexico.
At the wintering sites in Mexico, the butterflies roost in trees and form huge aggregations that may have millions of individuals.
They leave for the north in the spring, and females lay eggs along the way.
The females lay eggs singly on the leaves of the milkweeds (Asclepias); caterpillars eat the leaves and flowers.
and one that won't make it:
The chrysalis is light green, except for when the butterfly is about to emerge
female vs male:
Chrysalis just before emergence
Freshly emerged butterfly
There are extensive accounts of Monarch migration and ecology in technical and popular literature.
Compare the Viceroy
(below), an unrelated mimic. Easily distinguishable by the black stripe across the Viceroy's hindwings.
Relatives of the Monarch are: Queen