Monarch butterflies undergo complete metamorphosis. In this life cycle there are four stages:
The process of transformation takes about a month to complete (egg to adult) and it always takes place during spring and summer.
Monarchs are migratory butterflies, which means they spend their winters in southern, warmer areas and endure an arduous and long trip to arrive to their destination.
During the summer months, however, their native ranges are located in North America and their habitat spans from Southern Canada to the Midwestern United States.
The monarchs that migrate live for 7 to 8 months. These butterflies that migrate start the first generation of monarchs when they lay their eggs in Mexico, or the Southern United States, in early to mid March. Often times the first generation may take 40 to 50 days to fully develop from egg to adult.
The first generation starts their migration north in April and lays eggs along the way. By mid June, the second generation that was laid through much of eastern North America emerges and mates – and if they started their lives south they continue to migrate north.
Additional generations (three and four), that emerge in the north in mid July to August, will start their journey south as early as late August and may lay eggs along the way. A lot of the monarchs from the late generation will remain with immature reproductive organs and will cluster together in late summer traveling south. These generations will reach full reproductive maturity the following spring, when they will mate in their overwintering colonies. Their eggs will then become the new first generation.
Eggs Phenology and Ecology
The monarch egg is small (the size of a pencil tip, 0.9 to 1.2 mm), round, with ridges vertically from tip to the base. The shell of the eggs is lined with wax to protect the developing larva inside, and each egg has openings through which fertilization is possible. Often their color ranges from off white to yellow.
Eggs can be found attached to the leafs of milkweeds. The milkweed as a host plant is not chosen at random by the parents, but to later become food for the larva (caterpillar) after hatching. The larva (caterpillar) head can be often seen at the end of the egg stage (3 to 8 days) at the top of the egg. One female monarch can lay up to 700 eggs.
For the egg gestation to be successful, certain criteria have to be met especially on the habitat side. Human influence and the use of herbicides and pesticides have adversely affected the survivorship of the monarch butterfly. Recent research and news reports have suggested that in the last 30 years the abundance of milkweeds have significantly declined in midwestern states where crops like corn have been raised as a monoculture, and the culprit is partially it seems – evolution.
With the dispersal of Roundup (Glyphosate) as a main agent to combat invasive weeds in food crops, after a prolonged periods of time certain hardier plants have evolved to be herbicide resistant. Unfortunately for the milkweeds, these groups of plants, like the pigweed for example, not only have become more resistant – but more widespread as well.
Certain genetically modified seeds for crops have also been engineered to be herbicide resistant and with such competition the milkweeds have been all but virtually extinct on the agricultural landscape. With this scientists have noticed decline in the monarch populations in those same areas.
But it is not all grim as it may seem. New studies have shown that there is novel ways to extend the habitat of the beloved butterfly beyond gardening in our homes. In Oklahoma, scientists have been using prescribed fires to increase the density and abundance of milkweeds in range lands and have show that when done methodically and with the right timing it is directly tied to the increase in the number of eggs and larva of the monarch butterfly.
The future of the population of this colorful invertebrate is uncertain for now. In 2014 a petition to protect the Monarch under the Endangered Species Act was filed with the Fish and Wildlife service. Currently conservation plans are being evaluated and we are looking forward to the process of Conservation on federal level to begin in near future.
Conservation Efforts and More Information
The Xerces Society for Invertebrate Conservation has a long standing record of Monarch protection. Another great resource is the University of Minnesota website that details the life cycle, conservation efforts and gardening for monarchs: monarchlab.org.
An extensive Western Milkweed Species plant list can be found at the Western Monarch Milkweed Mapper Website, where a database of state by state species is detailed along with images and description.
If you want to know more, check out these other great resources: