The decline of the monarch butterfly population has led researchers to look for reasons why.
A popular theory is the loss of milkweed, the only plant on which monarch larvae feed. But a study from the Illinois Natural History Survey at the University of Illinois indicates that's not the sole culprit.
"It's multiple things coming together to cause this problem," said plant ecologist Greg Spyreas.
Monarchs migrate between Mexico in the winter to the midwest and Canada when the temperature warms. Fewer are making it to Mexico each year, as much as a 90% drop in 20 years. And there are fewer milkweed plants.
But a closer look shows more milkweed is available than previously thought.
"I would say the milkweeds in natural areas are buffering the loss of milkweeds in the agricultural areas (where they have been nearly wiped out)," said Spyreas. In fact, monarchs tend to see a population rebound while in this area, which would indicate loss of milkweed alone fails to fully explain the overall monarch decline.
He thinks other factors that could be stressing monarchs include loss of habitat, pesticide use, drought in the southwest along their migration route and even climate change.
But he also points out the push to add more milkweed is important as it plays a vital role for the insect. He said backyard and road side plantings have helped offset the loss of milkweed elsewhere.
"You don't necessarily need to have milkweed plants in these massive fields or massive, gigantic prairies in order to be effective," Spyreas said. "Monarch butterflies prefer to lay eggs on milkweed plants that are scattered because they tend to survive better."
If there is a positive for the monarchs, Spyreas said it's that people are paying attention.