An adult Monarch butterfly weighs about half a gram – less than the weight of a dime. It is astounding that such a delicate, light creature can also fly distances as vast as 2000-4500 km. The Monarch’s migration generally begins at the end of August for two reasons: 1) they cannot tolerate winter climates; and, 2) milkweed plants do not grow in the winter.
A Monarch butterfly’s life cycle, like those of butterflies in general, involves changes in form (metamorphoses) in four stages: egg, larva (or caterpillar), pupa, and adult.
Why is milkweed important to the Monarch butterfly? It is the ONLY plant on which their eggs are laid and subsequently, it is the ONLY plant which the hatching larvae (caterpillars) eat. The milky, sticky sap from the leaves is actually toxic to many other animals, but Monarch caterpillars, amongst other animals, can safely absorb those toxins, rendering the adults unpalatable to most predators.
Between migrations, there are generally four generations of Monarch butterflies. In February and March of each year, overwintering Monarchs will emerge from their dormancy, and as they migrate northwards, they lay eggs on milkweed along the way. The reproductive cycle continues and by the end of August, up to four generations will have evolved. This final (fourth) generation has been dubbed the “supergeneration,” for it is the one that will migrate southwards on its long journey, and live for seven to eight months, in contrast to the previous generations’ lifespan of four to six weeks.
Interestingly, Monarchs that live west of the Rocky Mountains migrate to Pacific Grove, near Monterey in California, whereas Monarchs living east of the Rockies migrate down to central Mexico. The exact location of where the Monarchs roosted in Mexico was a mystery until 1975. That year, Catalina (Aguado) Trail and her partner Ken Brugger stumbled upon the breathtaking site of millions of roosting Monarchs in the oyamel fir trees of the Michoacan province, near Angangueo. Trail and Brugger were participants in The Great Butterfly Hunt, the very first citizen science project, launched in 1935 by U of T professor Dr. Fred Urquhart. A new 3D IMAX film called Flight of the Butterflies opened in September last year (2012), and it beautifully showcases Urquhart’s story and the life cycle of the Monarch.
It is clear that milkweed is a critical element upon which the survival of the Monarch depends. Unfortunately, large declines in Monarch butterfly populations have been observed over the past two decades, largely due to a drastic reduction in milkweed across North America. As is the case with most aspects of pollinator declines, herbicide use and farming practices have led to a loss of 140 million acres of the vital milkweed plant.
Although Monarch butterfly larvae are host-specific for food, their activities as adult pollinators are more general, pollinating other plant species in addition to milkweed.
One of the researchers of the Monarch butterfly, and someone who was consulted throughout the filming of Flight of the Butterflies, is Chip Taylor. Taylor is the founder of Monarch Watch at the University of Kansas at Lawrence. Following is an excerpt from an interview with The Globe and Mail newspaper.
How are monarch populations being threatened?
Monarchs need the milkweed to lay their eggs?
If you don’t have the milkweed, you don’t have the life cycle.
Have we seen an impact on the monarch population?
Oh yes. We’ve published two papers showing there’s a statistically significant decline in the number of monarchs related to the development of use of herbicides on round-up ready corn and soybeans. Our population is now in the last ten years about 50 per cent of what they were in the previous ten years.
There are many groups that offer education on monarch conservation. Please plant milkweed! Learn more about the native milkweed species in your area, by consulting this resource, in conjunction with the Evergreen Native Plant Database. Check out the trailer of The Flight of the Butterflies, and browse the site to find a screening near you. You can learn more about helping monarchs here.
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