Monarch butterflies use plants for medicine

Humans aren’t the only creatures who improve their health with medicine. Monarch butterflies do, too. That’s according to Emory University scientist Jaap de Roode. He told EarthSky:

Monarchs are often infected with a parasite. Ophryocystis elektroscirrha, that’s a very long name. It actually makes the monarch quite sick. Those monarch butterflies won’t live as long. They don’t fly as well.

This parasite is also easily transferred from mother to offspring, de Roode said. In a 2010 lab experiment, he found that female monarchs infected with this parasite showed a strong preference for laying their eggs on top of a special variety of milkweed plant, called tropical milkweed. Tropical milkweed weakens parasites. The plant doesn’t help adult butterflies much, but when young caterpillars feed on it, their symptoms of disease are greatly decreased. He said:

The mother doesn’t cure herself. She really excels in this maternal care where she provides her offspring the medicine they need.

He said researchers are still trying to figure out how monarch moms know which variety of milkweed will help their young. De Roode said the mother’s behavior is instinctual, possibly guided by smell or taste. He said:

When you think about it, there’s this huge variety of plants, and a lot of animals use plants as their food. So in a way, it makes a lot of sense that there should be pressure for these organisms to evolve ways in which they could use that food to treat diseases.

De Roode clarified that monarchs use milkweed as an important food source in their day to day lives.

There are many different species of milkweed. There’s not just one. There are several hundred, probably. But the point is that monarchs can use between 20 and 30 of them as their food.

He said that while special varieties might kill off parasites, milkweeds in general protect caterpillars and butterflies from predators.

Monarchs are very well known to take advantage of these chemicals, called cardenolites. These are toxic chemicals. If we eat milkweeds, we get sick. Monarch caterpillars do not get sick. They take these chemicals inside their own bodies, and that makes those caterpillars and the monarch butterfly that comes from those butterflies toxic to predators. In other words, if we feed that monarch butterfly to a bird, that bird will get sick. It will throw up, and learn not to touch the monarch again.

He said this older body of knowledge is what led him to find out how milkweed affected the butterfly’s own health. De Roode added that his discovery about butterflies’ use of plant medicine is important because people often attribute use of plant medicine to learned or cognitive abilities. But de Roode said that many creatures in the wild – from insects to primates – appear to have a ‘sixth sense’ for plants. In other words, there’s some kind of instinct that guides them to medicinal plants. He told EarthSky:

What we could do is look at all these animals out there that have co-evolved with their parasites for many, many millions of years in their natural habitats. I think we could look at the animal world and say: How do these animals cope with their diseases? What plants do they use to cure themselves and their offspring of diseases? If we can find that, can we go to those plants and determine the chemicals that provide us protection? And can we use those chemicals to create drugs for our own diseases?

June 21, 2012

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Beth Lebwohl

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