Zoology

Migration Patterns of the Danainae Butterfly



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The danainae, or milkweed, butterfly is a subfamily of the family Nymphalidae (brush-footed butterflies). This butterfly is also known more popularly as the monarch butterfly as it is considered the "king" of butterflies and the most beautiful.  It is referred to as the “milkweed” butterfly because the larvae eat only milkweed plants for about two weeks before they develop into caterpillars.  The caterpillar then transforms into a pupa, which later emerges as a butterfly.  

Monarch butterflies cannot live in the cold climates of northern winters, and since they do live in northern areas during the summer, they must migrate with the approach of fall. The migration usually starts in October but can start earlier if weather is cool. Monarch butterflies are the only known insect that can migrate as far as 2,00 miles each year. 

Not all monarch butterflies participate in this migration.  Monarch butterflies go through four generations each year. The first three generations, after hatching from their cocoons, live for only about six weeks.  However, the fourth generation lives for six to eight months.  This generation migrates to the warmer climate during the winter, hibernates, and then gives birth to a new first generation in the spring.  One might ask the question, why do these butterflies bother spending any time in the north at all, if they cannot live there during the winter?  The reason is simple.  The milkweed plants that are the sole food source for the larvae only grow in the north.

The migration patterns of butterflies have been the topic of much inquiry over the decades.  Dr. Frederick Urquhart is considered the founder of studies of the monarch butterfly migration.  Born in Toronto, Ontario, he became the assistant director of zoology at the Royal Ontario Museum, and later, in 1966, he became one of three initiators of the zoology teaching and research program at Scarborough College. He passed away in 2002, at the age of 90.

In 1945, Dr. Urquhart married Norah Patterson, and together, they formed the Monarch Team out of their home in Toronto.  They experimented with tagging methods, marking and releasing individual butterflies in the hope of sighting them later in their new locations. Tiny adhesive tags were developed and labeled, “Send to Zoology University Toronto Canada”.  Before long, small boxes of the tagged monarchs began to arrive at the Urquharts’ home.

An appeal was made by the Urquharts for volunteers to assist in the marking project.  With the help of the volunteers and thousands of other participants in the project, much information was uncovered, including the fact that not all of the butterflies were migrants.  It was also found that, for those that did migrate, there was a directional pattern, from northeast to southwest.  Ken Brugger, a young engineer, later became a very important contributor to the project when, in 1975, he found the destination of monarchs that had migrated from the northeast.  So, in 1976, the Urquharts traveled to the Neovolcanic Plateau, about 240 miles from Mexico City, to see the millions of butterflies that awaited them as a reward for their 40 years of research.

The study of the migration of the monarch butterflies continues in earnest even today, and anyone can help. The Journey North website has a place where butterfly enthusiasts can report seasonal sightings of monarch butterflies. The website also has maps of the most recent butterfly migrations, from the spring of 2013.  

Sadly, though, the most recent data on monarch migration are showing that the butterflies are suffering due to environmental conditions.  The Monarch Survey, a joint project of Mexico’s National Commission of Protected Areas, the World Wildlife Fund and Telcel, a Mexican company, reported that in 1996-1997, 18.19 hectares were occupied by butterfly colonies. However, a current survey from the spring of 2013 found that only 1.19 hectares is now occupied by the butterflies.  Lincoln Brower, biology teacher at Sweet Briar College in Virginia and a leading expert on the monarch butterfly, believes that use of the herbicide glyphosate, developed by Monsanto and more notoriously known as Roundup, has become a critical threat to milkweed, the monarch food supply.  Development of once-wild coastal areas also threatens their overwintering spots.

Climate change and fluctuations also affect the survival of monarch butterflies. Efforts are being made, however, to help preserve the monarchs.  Insect ecologist Chip Taylor, of the University of Kansas, is encouraging the creation of monarch waystations. These little stopping points along the butterfly migration routes are like rest stops along the highway for humans.  The butterflies can stop, take a rest, and get the resources that they need to survive.

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ARTICLE SOURCES AND CITATIONS
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