Global warming may poison monarch butterflies, study finds

Monarch butterflies depend on milkweed and its poisonous compounds that are deadly to most other insects. But a new study finds global warming may be making the very plant monarch butterflies need to survive too toxic even for them. Their vibrant red-orange wings with contrasting black veins and white dots make monarchs (Danaus plexippus) easy to recognize not only to humans but also to birds on the lookout for a snack. It’s a warning that tells would-be predators an important message: Poisonous – do not eat. Monarchs get their protective poison from the milkweed plant, which is actually a group of species nested under the genus Asclepias. The great Swedish botanist and founder of modern taxonomy Carl Linneaus named this group after Asclepius, the Greek god of healing, because of the plant’s use in traditional medicine. But milkweed plants also have a deadly side. They produce compounds called cardenolides that are steroids capable of stopping the heart. Scientists believe milkweed plants produce cardenolides as a defense against plant-eating insects and other animals. But some species have coevolved around this defense. And some, like monarch butterflies, don’t just cope with these toxins – they’re able to sequester them in their tissue to make themselves poisonous and bad tasting to their own predators. A monarch caterpillar feasts on a milkweed leaf. Photo by USFWS Mountain-Prairie Because of their unique defense, monarch butterflies are obligate feeders on milkweed, and their caterpillars cannot eat anything else. This relationship is a risky one, and monarchs…

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