Category: Insects, Spiders, & Others

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 Bessler, Photo 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:

A San Francisco Butterfly: The Variable Checkerspot

Cover photo: © Jamie Chavez, 2013, some rights reserved.

Learn more about the small butterfly that’s making a comeback around the San Francisco Bay Area.

Cover photo: © Jamie Chavez, 2013, Flickr Photo Album, some rights reserved.

The Presidio’s population of variable checkerspots became locally extinct in 1978.

Variable checkerspots are a part of a program working to reintroduce native species back to the Presidio in San Francisco. The Presidio’s checkerspot population became locally extinct in 1978 due to the loss of habitat. Park restoration efforts are currently working on the Presidio’s native habitats, resulting in 50 acres of native habitat restored thus far. With the hopes of bringing the butterflies back, 1,500 caterpillars were collected from other parts of the Bay Area and reintroduced to the Presidio in 2017.

If successful, the Presidio will become one of two areas in San Francisco that hosts the variable checkerspot butterflies (the other at Laguna Honda Reservoir). The primary cause of their decline in the area has been the loss of habitat across the city. With efforts such as those at the Presidio, we can hope that we’ll be seeing more of this beautiful butterfly.

Variable checkerspot caterpillars are spiny, and the butterflies are black with checkers.

Variable Checkerspot caterpillars are mostly black, with light dots that form bands along their body. They are covered in black and orange spines.

Butterflies are mostly black-brown, with yellow and orange checkers. Their wingspan is 1.25 – 2.25 inches.

Variable Checkerspot Caterpillar
Variable Checkerspot caterpillar on an English Plantain at Purisima Redwoods Preserve

Variable checkerspots live on the west coast of the U.S.

Variable Checkerspots can be found along the Pacific Coast,and as far inland as Wyoming and Colorado. They prefer chaparral habitats (semi-arid areas composed of mostly shrubs), open forest areas, and alpine tundras.

Variable checkerspots use many native and non-native plants for food.

Caterpillars will use beeplant, Indian paintbrush, snowberry, honeysuckle, monkeyflower, English plantain, and many others as host plants. Adults will feed on nectar from California Buckeye, Squawbush, Yerba Santa, and thistles (to name a few).

Resources to learn more: