Biology and Migration

Monarch Butterfly

Danausplexippus

Biology and Migration

The monarch butterfly is a pollinator (an insect that carries pollen from one flower to another). It has four life stages: the egg, the larva (caterpillar), the pupa (resting stage or chrysalis) and the adult butterfly.

Adult monarch butterflies lay eggs in March and April on milkweed plants. The eggs hatch after about 7-10 days. Dry conditions and temperatures above 95F(35C) can be deadly to the development of the butterfly and to milkweed plants as well. When the eggs do hatch, the caterpillars will feed on the milkweed plants.

Milkweed contains toxins (poisons) that are harmless to the monarch. However, these toxins remain in the adult monarch’s body making poisonous to its predators. An adult monarch will feed on nectar from a variety of flowers including milkweeds.

In spring, summer and early fall monarchs can be found wherever there are milkweeds. Monarchs cannot survive freezing temperatures and neither can milkweed. So in the winter, monarchs from the east of the Rocky Mountains overwinter (spend the winter) in the Oyamel fir forests in central Mexico.

An adult Monarch typically lives four to five weeks, but each autumn a special group emerges. These special butterflies will live seven to eight months, and they are born to make an incredible journey. When the days begin to get shorter and the air gets colder, the butterflies sense it is time to migrate (to move or travel to another area or region, sometimes at regular or annual times).

Early fall, as many as 100 million monarch butterflies migrate from northern parts of North America to California and Mexico. Monarchs can fly up to 3,000 miles (4,500 km) just to reach their overwintering place. It may take monarchs up to two months to reach their final destination. The final destination is an environment that is cool and moist. Monarchs will gather on trees forming clusters to stay warm. The temperature ranges from 32F - 60F (0C - 16C). When warmer temperatures arrive in March, this will signal the monarchs to begin the journey back north.

When spring comes it is finally time to journey back north. The Monarchs that overwintered in Mexico will make it about halfway to their summer habitats before they lay their eggs and die. It will take about four more generations of their shorter-lived offspring to complete the journey.

Environmental Science – Global Changes

Although the monarch butterfly is not on the endangered species list, their yearly migration is considered an endangered event. Monarchs are in danger of losing their summer and winter habitats. Summer habitats are destroyed as more houses, roads and businesses are built. As the land is cleared,milkweed is killed. In many places people use chemicals to kill milkweed. Winter habitats have been damaged and lost as the land is logged (to cut down trees) and cleared for homes and farms. Lastly, climate change has also been threatening the monarch’s migration. Colder, wetter winters could be deadly to the butterfly and hotter, drier summers could shift suitable habitats north. Unusual patterns of drought and rainfall could have an effect on milkweed plants.

Conservation – How to Help

To help, people in many places are planting milkweed plants in their gardens, yards and schoolyards. These plants provide places for monarch butterflies to lay their eggs,food for caterpillars and nectar for adults. Other flowers that are planted will also provide important nectar for these butterflies.

Resources

BioKids

Monarch Watch

Journey North

Exploring Nature Educational Resource

National Geographic Kids

Credits

Caterpillar photo by Ryan E. Poplin [CC-BY-SA-2.0], via Wikimedia Commons