Monarch butterflies are the only butterfly species to complete a two-way migration, and indeed their yearly journey from Canada to Mexico, South Florida, and coastal California is a magnificent feat. But, warming temperatures and prolonged droughts brought on by climate change are impacting when and how far the butterflies travel, which in turn can harm their reproduction numbers.
What’s going on?
Monarch butterflies cannot survive the cold, so every winter, they migrate to Mexico, South Florida, or coastal California to roost, or rest. Many of the butterflies only make one leg of the journey due to their short life cycles. The path of this migration is genetically ingrained in monarchs so if they perish during their travels, their offspring continue the journey.
This migration is triggered by a drop in temperature that tells the butterflies it’s time to head south. Warming temperatures caused by climate change can lead to delayed migration.
If the migration is delayed, the temperatures are already too cold for the butterflies by the time they make their way to the Midwest. The higher temperatures can also cause summertime breeding sites to be driven further north, which would make the migration south longer and more difficult.
Climate change driven droughts and new agricultural techniques in North America have also caused a decrease in their main source of food—milkweed. Additionally, increased levels of carbon dioxide in the atmosphere may cause milkweed to overproduce toxins called cardenolides, which would make the plant too toxic for monarchs to tolerate.
Why it matters.
- Scientists have predicted that in the next 20 years, there is an 11 to 57% chance that the monarch butterfly numbers could drop so much that the species will not be able to recover.
- Monarchs are important pollinators and play an essential role in many ecosystems’ ability to survive.
- Monarchs are also culturally significant and play a big part in environmental education for children and families.
What you can do.
- Plant milkweed that is native to where you live for monarchs to lay eggs on and for caterpillars to eat.
- Plant native nectar-rich plants for butterflies to eat.
- Encourage agricultural landowners to replant milkweed they may have removed.
- Educate others on this topic and encourage them to get involved.
Information from National Geographic, Florida State Parks, Environmental Defense Fund, and The Nature Conservancy.