Heat Poisoning?

Could monarch butterflies’ favorite food someday become too poisonous for them to eat? A recent study shows that might be the case as climate change causes temperatures to rise.

Monarch caterpillars feed exclusively on the leaves of milkweed plants, which contain a toxic steroid called cardenolide. Monarchs have developed a tolerance to this poisonous compound. It even protects the butterflies by making them unappetizing to predators. In exchange, monarchs spread milkweed pollen and help the plants reproduce.

To learn how climate change might affect this relationship, scientists grew a particular species of milkweed at temperatures we expect to be common in 40 years. They found the plants produced more toxin.

“If a milkweed plant produces too much toxin, monarch caterpillars die,” says Bret Elderd, a biologist at Louisiana State University involved in the study. And that’s bad news for monarchs.