The Monarch Butterfly
Scientific name: Danaus plexippus
Wingspan: 3 3/8 - 4 7/8 inches
Life span: takes a month to become an adult; dependent on season pupa emerges; longest is nine months
Description of egg: spherical, ridged and white; of caterpillar: banded with cream, black & yellow stripes; of adult: bright orange with black wings; white spots on outer margins with three orange patches on top; body is black with white spots
Differentiation between sexes: females thicker, black wing margins; males have small claspers on body, distinguishing black spot on its wings
Habitat: found in open areas - meadows, marshes, pastures and fields
Migration: some fly over 2,000 miles to overwinter in southern California coasts to the mountain regions of central Mexico; some will stay in one place for all their life
Diet: caterpillars - own shell, then only consumes the poisonous milkweed; an adult uses its proboscis to sip the nectar of various flowers
Predators: insects, spiders, birds, small vertebrate; viruses & bacteria are more likely killers of Monarchs
Defense: poisonous - built up this poison from milkweed during the larval stage; coloration of bold colors is used as a warning to predators
The North American Viceroy (Limenitis archippus) is very similar to Monarchs in size, shape, coloration and pattern. Lucky for them as predators who have learned to avoid the Monarch is likely to avoid the Viceroy as well.
The Life Cycle of the Monarch Butterfly
All butterflies will go through a complete metamorphosis in four stages – egg, larva, pupa and adult. For the Monarch butterfly, metamorphosis will take about a month.
A female will lay a single egg at a time, usually on a leaf of the milkweed plant. It is hard to determine how many eggs a female will lay in its lifetime, but it is believed the number is somewhere between 100 and 300. Eggs will hatch four days after being laid.
Once hatched, the butterfly enters its larval stage, commonly known as its time as a caterpillar. The Monarch caterpillar is distinguished by its bands of cream, yellow and black. During this stage, the caterpillar spends most of its time feeding on its singular diet of poisonous milkweed. This consumption of milkweed is built up so as an adult, the Monarch is poisonous to those that eat it – its one defense against predators. As the caterpillar gets bigger, it will molt (and then consume its shedding). This shedding occurs five times during the larval stage.
The next stage – the pupa stage – is when the caterpillar makes its greatest transformation. At this point, the larvae will encase itself in a chrysalis, a smooth, hard-shell casing where its body tissues and organs are broken down and re-arranged to create the adult. This is the Monarch's most vulnerable stage as it has limited ability to move if threatened by predators or adverse weather conditions. Its jade-colored casing is well camouflaged in order to elude potential threats.
When the Monarch materializes from its chrysalis, it emerges as a beautiful butterfly of deep orange, black and white. As an adult, their main duty is to reproduce, and will do so several times in their life. The monarch’s lifespan varies depending on when they emerge as a pupa and whether or not it will migrate. Those that are born in the early summer will have the shortest life – about two to five weeks. Monarchs that emerge in the late summer and migrate south will live much longer, around 8 – 9 months. Many of these Monarchs will experience the longest migration route for any butterfly in the world - a truly unique phenomenon.
There and Back Again: The Monarch Migration
Every autumn, around three million Monarch butterflies will travel around 3,000 miles to inhabit the mountains of central Mexico or small groves of trees along California’s coast. But why? Monarchs are cold-blooded insects that cannot survive the long, cold winters of temperate climates. If these butterflies failed to take off, they will most likely perish. Their migration is a natural, survival instinct that has amazed people around the world as there is no other North American butterfly that migrates the way that most birds do.
There is a difference between butterfly and bird migrations. While most of the birds that fly south for the winter always return, butterflies do not. Instead the adults continue to mate and reproduce then die. It is their offspring (and their offspring’s offspring) that somehow know they must return north and how to do so. There are many questions researchers and scientists have about the Monarch butterfly that are left unanswered. For instance, how do those that didn’t make the trip south know how to get back north? Or how do following generations of Monarchs know exactly where to go to overwinter in the first place?
According to Monarch Watch – a University of Kansas site dedicated to the education, conservation and research of the Monarch – overwintering sites are dependent on where the butterflies migrate from. Butterflies west of the Rocky Mountains will return to the California coast. Millions of monarchs east of the Rockies will migrate to the Transverse Neovolcanic Mountain Belt in central Mexico. Regardless of where they are overwintering, the sites are very similar. The most important element is great stands of trees where the monarchs can cluster together. The surrounding habitat – underbrush, stream, fog and water – is also necessary in order to protect the butterflies from wind and snow as well as provide moisture and a cool place as to not use up their reserved energy.
In order to understand the migration instincts of the Monarch, researchers began tracking the butterfly. This ever-expanding project began in 1937 with F. A. Urquhart who started tagging the wings of the butterflies. The project grew as he started to enlist volunteers across the country in his Insect Migration Association. His research provided new information on where Monarchs overwinter in California. Although this particular project ended in 1977, many other organizations followed Urquhart’s lead and have continued monitoring Monarchs all over the world. Monarch Watch, Journey North and Monarch Alert are just a few of these organizations still working today.
Why Should We Care?
With millions of Monarchs in existence, it would sound foolish to say that they are in danger of being endangered. The truth is that there are many organizations and researchers concerned over the overwintering habitats Monarchs need in order to survive. There are only eleven to fourteen mountain tops in Mexico where these butterflies can find a safe haven to wait out the harsh winters in temperate climates. These areas are being targeted for new roads, housing developments and agriculture expansion. In the southern coastline of California, the stands of eucalyptus trees, Monterey pines and Monterey cypresses are in danger of being cut down due to the rate of land development in the surrounding area. If we do not concern ourselves with the possible destruction of these sites now, we may have to worry about the extinction of Monarch butterflies sooner than we would expect.