Migrations: The Monarch Butterfly

Cover photo: © 2017, Mike Bessler, some rights reserved.

Did you know that there is a species of butterfly that migrates south in the winter? Meet the monarch, one of California’s most interesting butterflies.

Cover photo: © 2017, Mike BesslerPhoto Library (Flickr), some rights reserved.

Places to See Monarch Butterflies

Monarch butterflies make an annual migration to warmer temperatures, with some populations traveling as far as 3,000 miles.

Millions of monarch butterflies undergo an annual migration, just as birds migrate south in the winter to escape cold temperatures. Cooling temperatures, shorter days, and the aging of milkweed (the primary source of food for monarch caterpillars) signal to the butterflies that it’s time to begin the journey south. Upon reaching their destinations, the monarchs congregate together and form large clusters on the branches of trees. This allows the insects to retain enough warmth to survive the winter.

You can see this migration in the Bay Area! From mid-October to mid-February, the monarch butterflies overwinter at Lighthouse Field State Beach and Natural Bridges State Beach.

For more information on their migration, check out this Bay Area Naturalist article.

The western population of monarch butterflies has been facing declines over the past 20 years.

In 2018, citizen scientists recorded the lowest numbers of monarch butterflies seen in California for 5 years. According to one source, 1.2 million butterflies were recorded on a California survey two decades ago. In 2018, a survey using almost the same number of locations recorded just 300,000 butterflies.

A recent study conducted by a Cornell University scientist posits that loss of overwintering habitat, the loss of habitat for butterflies to stop during their migration, and the declines of sites with nectar-producing flowers for adults during their migration are the main causes of the monarch butterfly declines.

You can help participate in the counts that help scientists know the status of monarch butterfly populations! For more information, check out the Western Monarch Count’s page on volunteering.

Monarch butterflies are vibrant orange.

Monarch butterflies have unmistakable orange wings, with black veins creating beautiful windows in the color. The caterpillars are just as vibrant, with black, yellow, and white stripes across their bodies.

The viceroy butterfly is a species that mimics, or copies, the physical appearance of monarch butterflies. Can you tell the difference in the photo below?

Image result for viceroy vs monarch
Monarch versus viceroy butterfly; Source: Socratic.org

Monarch caterpillars only eat milkweed.

Milkweed plants are rich in toxic chemicals called cardenolides. Monarch caterpillars, which feed exclusively on milkweed, are able to store the chemicals in their bodies through adulthood, making adult monarch butterflies bitter-tasting and potentially toxic to predators.

Monarch butterflies don’t specialize on one type of plant like the caterpillars do. They will consume nectar from a variety of flowers.

Monarch butterfly males and females look different from one another.

Male monarch butterflies have a small black spot in the middle of their hindwings (their bottom pair of wings). These “spots” are actually areas that emit chemicals for the courtship displays of some butterflies; however, the spots are not known to be important in the courtship displays of monarchs.

Male and Female Monarch Butterfly
Male versus female monarch butterfly; Source: gardenswithwings.com

Cool facts about monarch butterflies:

  • Only one generation of monarch butterfly migrates out of the 4-5 generations of butterflies that live each year. The generation that migrates is termed the “migratory generation”.
  • Monarch butterflies weigh between 0.27 and 0.75 grams. For some perspective, a U.S. quarter weighs 5.67 grams.

Resources to learn more:

Author: Taylor Crisologo

Taylor studied biology at Cornell University, where she worked with the Cornell Lab of Ornithology on projects ranging from breeding herring gulls off the coast of Maine to dancing lyrebirds in Australia’s Blue Mountains. When she’s not researching great places to experience Bay Area nature, you can find her birding or reading a book at home with her husband and their two indoor cats (Max and Penelope).

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