The Monarch Butterfly (Danaus plexippus)
The monarch butterfly, Danaus plexippus, is a widespread insect species. In North America, it is a most characteristic large, ornate butterfly. There has even been an effort in the United States to adopt the monarch as the national insect. Moreover, D. plexippus is the only insect listed by the Bonn Convention for the Conservation of Migratory Species of Wild Animals. In fact, the extraordinary attention that the butterfly has received over the years has led some authors to doubt whether it is justified. The monarch butterfly certainly is not endangered; actually, relatively large numbers of the organism exist. Perhaps it is the monarch's combination of intriguing characteristics though, which have made it the focus of so much scientific investigation.
Butterflies, in general, show a great diversity of biological features. The most important of these probably involve the organism's life cycle. The insects undergo "complete metamorphosis." Female adults lay eggs which give rise to larvae, or caterpillars. These larvae then grow by a series of moults, or instar stages, and eventually transform into a resting stage (i.e., the pupa or chrysalis). It is during the chrysalis stage that the organism's body is broken down and reorganized into the adult butterfly form. Variations on this basic pattern generally occur either between butterfly groups or species. These variations typically represent some attempt to make optimal use of seasonally available resources within a given organism's habitat.
The monarch belongs to the Danainae group of butterflies. These diurnal Lepidoptera comprise approximately 150 inter-tropical species. The common name for the insects is the "milkweed butterflies." This derives from their widely exploited host plants. Milkweeds possess a white sap that contains numerous chemical substances which are either poisonous or distasteful to animals. ...