Fast Facts: Monarch butterfly

Scientific name: Danaus plexippus
Average weight: Caterpillars are 1.5 grams
Butterflies are 0.41 grams
Average wingspan: 93 to 105 mm
Average lifespan: 6 to 8 weeks for summer generations
6 to 8 months for winter generations

Did you know?

Monarchs have the longest and largest insect migration in North America, traveling up to 8,000 km per year!

Physiology

Monarch butterflies are probably the most well-known butterfly in North America. But monarchs aren’t born with the patterned wings we know so well. The monarch only becomes a butterfly in adulthood, after it makes its way through four different stages of its lifecycle: egg, larva (caterpillar), pupa (chrysalis) and adult butterfly. The transformation from one stage to another is called metamorphosis. The full cycle to adulthood takes about 30 days to complete, although monarchs born in the spring often take longer to develop because of cooler conditions.

The female usually lays her eggs on the undersides of milkweed leaves. After three to eight days, depending on the temperature, the egg hatches and the larva emerges, feeding on its egg shell before going on to eat the milkweed leaf. Unlike most caterpillars, monarchs don’t blend in with their surroundings. Instead, they have bold yellow, black and white stripes to warn predators to stay away. The monarch spends about eight to 12 days as a caterpillar, molting or shedding its skin five times as it goes through five larval instars. Before the final molt, when it is ready to enter the pupa stage, the monarch attaches itself to a twig or another sturdy object and sheds its skin to form a protective casing around itself. After nine to 13 days, the pigment on its scales develops, revealing the butterfly within. When it emerges, the adult butterfly shows off brilliant orange wings that are marked with a thick black border and two rows of white spots.

You can tell apart the male and female adults from the patterning on their wings. Male monarchs can be distinguished by the two black spots on their hind wings, while female monarchs have a slightly thicker black border. Like other insects, the monarch has antennae or feelers that it uses for its sense of smell.

Habitats/Behaviours

Monarchs have the longest and largest insect migration in North America and some butterflies will travel thousands of kilometres during their short lifespan. However, individual butterflies do not complete the whole round-trip migration from the regions of northern Mexico to southern Canada. Instead, the cycle takes place over four generations. The offspring of the overwintering generation begin their lives in northern Mexico and the southern United States, migrating northward in the late spring and laying their eggs along the way. The second and third generations of monarchs continue to reproduce, but only monarchs born in late summer join the fourth generation in migrating to central Mexico, where they will then spend the winter.

The reason monarchs are able to fly such great distances is because they know how to save their energy. During migration, monarchs conserve their energy by riding columns of rising warm air and taking advantage of strong winds to help speed up their flight.

Range

Monarchs are true migrants and can be found in many areas of the world. In Canada, their natural habitat includes southern Alberta, Saskatchewan,Manitoba, Ontario,Quebec and the Maritimes. The monarch has also been found in other areas of the country, including locations as far north as James Bay.

Links:
Monarchs in the Classroom www.monarchlab.org
Monarch Larva Monitoring Project www.mlmp.org

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