This year's fall monarch butterfly migration through Texas appears smaller and is happening later than usual, according to observers. Researchers believe both changes are signs of how climate disruption is affecting the iconic butterflies.
Many factors impact the monarch population annually, but the biggest one is the availability of milkweed, the plant on which the insect lays its eggs.
In Texas, the severe drought that gripped the state through the summer and into the fall likely decreased not only available milkweed, but also other flowering plants that provide food for the monarchs.
"The butterflies are going to have trouble getting through Texas,” Chip Taylor, the outgoing director of Monarch Watch, told KUT in September.
That prediction seems to have been correct, with smaller numbers of butterflies making it to their winter grounds in Central Mexico.
Many of the butterflies still being spotted in Texas appear to be in no hurry to leave. That’s likely because fall rain and continued warm weather have brought fresh plant growth to much of the state.
“I’m actually sitting in my backyard right now and I’m watching a monarch butterfly,” Monika Maeckle, who tracks the insects and runs the website Texas Butterfly Ranch out of San Antonio, told KUT last week. “It’s a crazy weird year.”
Monarchs are less likely to undertake their migration as long as warm weather and milkweed are available where they live.
“The butterflies you’re seeing right now, they were born in the last month, so that would mean they were born in October or early November,” Maeckle said. “In San Antonio, we're still find some eggs on milkweed that’s around. So it’s like the whole cycle is being pushed.”
Observers at the monarchs' winter grounds in Mexico say they are still seeing some stragglers arriving. But some research shows these late-season butterflies are less likely to even undertake the migration.
“If we don’t have cold weather it’s like, ‘Why don’t I just stay here?'” Maeckle said. “There’s milkweed … what’s the motivation?”
Climate researchers say both extreme drought and warmer winters are the result of global warming caused by manmade greenhouse gas emissions.
Conservationists worry that those trends may, one day, end the great monarch migration to and from Mexico every year, leaving remnant populations of non-migrating monarchs.
“You see this already in Florida and Houston,” Maeckle said, “coastal cities where there’s local populations of year-round monarch butterflies.”
