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Sven Explains: Monarchs, milkweed and climate change

Monarchs need to find milkweed after mating, but sometimes, the milkweed isn't ready for them.

ANGANGUEO, Michoacán — Milkweed is crucial to Monarch butterflies. 

It's the sole food source for Monarch caterpillars. 

But there is a concern that a warming climate is causing Monarchs to mate and migrate earlier in the spring. 

This can be dangerous, because if they leave too early and hit cold weather in the U.S., the milkweed might not be ready for them. 

"When the days are getting warmer, they will mate and they will fly back to find the milkweed in Texas and Louisiana." Biologist Patricia Valdespino said.

It's a trend that scientists have been seeing. Valdespino said that every year, they're moving a little bit earlier. 

That's likely a result of climate change, but if they leave too early it can be catastrophic. Monarchs will die without the milkweed they need to lay their eggs in.

"If the milkweed is not ready, they may not lay the eggs and they might die before laying the eggs,"  Valdespino said. "That would be very dangerous for the population. They will lay the eggs in the milkweed, and then the females will die."

Planting native plants like milkweed is important. We've developed too much land for agriculture and lawns - we need more milkweed.

After the Monarchs lay their eggs in the milkweed, it's time to head back to Central Mexico. They always make it there by November 1st. 

If you'd like to track the Monarch butterfly migration as it happens, check out this interactive map or visit journeynorth.org!

More from Explore With Sven:

Explore with Sven: Monarchs migrating to Mexico

Sven Explains: Counting millions of Monarchs

Sven Explains: Giant bee rediscovered after 38 years 

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