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Metamorphosis - April 9, 2008



The monarch butterfly (Danaus plexippus) is one of the most recognized species of butterflies in the United States due to the brilliant orange and black coloration.   It is one of possibly three species of the genus Danaus.  The other two are found outside the U.S.  One is in South America in the Amazon and the other is in Jamaica and Hispanola.  

The distribution not only includes the United States but, according to Wikipedia,  also Australia, the Canary Islands, Madeira, and as a migrant in Spain, Sweden, Russia, and the Azores,

Wing span of the species is approximately 8.5 to 12.5 cm with males slightly larger than females.  Males also have a pair of characteristic spots on their hindwing from which they release pheromones to attract females during breeding season.

Monarchs are noted for their migratory patterns, the most famous perhaps is the migration of the Rocky Mountain monarchs to regions in Mexico.  Life spans may be anywhere from 20 to 80 weeks (again according to Wikipedia) but most that make the migration are those born in late summer.  They enter a state known as diapause and may live an additional 5 to 6 months as they overwinter.  In the spring, they breed and begin the migration back north.  They never make it but 2 or 3 generations later, offspring from these do make it back to their home territory.  Monarchs in our area may stay the entire year and not migrate.

Spring is breeding season and it begins with the male secreting pheromones to attract the female and then flying together with the male trying to force the female to the ground.  Once grounded, the female receives a spermatorphore from the male to fertilize her eggs.

Eggs are deposited on milkweed plants and when the eggs hatch, the larvae or caterpillars feed on the egg cases and then on the milkweed.  The caterpillars store cardenolides from the sap of the milkweed which renders the caterpillar, and, later the adult, inedibile and toxic.

The caterpillar feeds to store fat and nutrients for the pupal stage.  At a certain point, the caterpillar attaches to a surface and begins to form the cocoon or chrysalis by molting to form a green covering over the body.  It remains in the cocoon for approximately 2 weeks.  The markings on the chrysalis are quite distinctive and there are often metallic, iridescent spots.  The chrysalis becomes transparent and you can see the orange and black wings inside.  

The chrysalis breaks at the top and the adult emerges with shrunken, wet wings.  It pumps fluid into the wings to get the full shape and then the wings are dried in the air.  Only when the wings are completely dry does the adult take flight.

© Fred Searcy 2017