November 21st, 2020 - Lyndsay NicoleThe Monarch butterfly (Danaus plexippus) is a very familiar species due to its size and striking pattern of orange, black, and white. Life begins when eggs are laid on the leaves of the poisonous milkweed plant, the preferred food of the Monarch caterpillars.
The toxins created by the milkweed, called glycosides, are its defense--intended to keep animals from being able to eat the plant. Because only the caterpillars of the Monarch have adapted to be unaffected by the defense, Monarch caterpillars are able to eat leaves of the milkweed and store the glycosides in their own bodies, which makes the caterpillar toxic.
Adult monarchs retain the toxins, but the obvious coloration of the Monarch butterfly makes it an easy target for a predator such as a bird. If a bird eats a Monarch butterfly, the toxic plant glycosides stored in the butterfly make the bird sick. Remembering the color pattern of the butterfly, the bird learns from the experience and no longer is interested in eating Monarchs. Within that bird's territory, other Monarchs can fly about unmolested.
This poison is similar to Digitalis, which can be used to help people with heart problems, but could actually kill a human if they consume too much of it! This toxin is poisonous to most vertebrates (animals with backbones), but they may not be poisonous to invertebrates (animals without backbones).
The potency of a Monarch Butterfly depends on the plants they ate when they were caterpillars. Some kinds of milkweed have higher levels of toxin than others. For example, Monarchs in the North have a different chemical makeup because the milkweed they eat is different from the milkweed found in the South.
The effect of the toxin depends on the amount of toxin that the predator eats, and what kind of animal the predator is. There are some birds that eat monarchs, some mammals (mice), several insects, and some parasites. We don't know much about the insect predators, but the birds have evolved interesting ways to handle the toxins in monarchs.
The two bird species that eat monarchs in the Mexican overwintering colonies have evolved to tolerate these toxins, and this is apparently true of the mice as well. Of five species of mice that are common around the overwintering sites in Mexico, only one eats Monarchs; the scansorial black-eared mouse. These mice have somehow overcome the Monarchs' chemical defenses enough to use them as an important food source during the winter.
Journey North
Henderson State University
Science Friday
November 21st, 2020 - Lyndsay Nicole - Fly Monarca Expedition
Adult monarchs retain the toxins, but the obvious coloration of the Monarch butterfly makes it an easy target for a predator such as a bird. If a bird eats a Monarch butterfly, the toxic plant glycosides stored in the butterfly make the bird sick. Remembering the color pattern of the butterfly, the bird learns from the experience and no longer is interested in eating Monarchs. Within that bird's territory, other Monarchs can fly about unmolested.
Don't eat the Monarchs!
This poison is similar to Digitalis, which can be used to help people with heart problems, but could actually kill a human if they consume too much of it! This toxin is poisonous to most vertebrates (animals with backbones), but they may not be poisonous to invertebrates (animals without backbones).
The potency of a Monarch Butterfly depends on the plants they ate when they were caterpillars. Some kinds of milkweed have higher levels of toxin than others. For example, Monarchs in the North have a different chemical makeup because the milkweed they eat is different from the milkweed found in the South.
The effect of the toxin depends on the amount of toxin that the predator eats, and what kind of animal the predator is. There are some birds that eat monarchs, some mammals (mice), several insects, and some parasites. We don't know much about the insect predators, but the birds have evolved interesting ways to handle the toxins in monarchs.
The two bird species that eat monarchs in the Mexican overwintering colonies have evolved to tolerate these toxins, and this is apparently true of the mice as well. Of five species of mice that are common around the overwintering sites in Mexico, only one eats Monarchs; the scansorial black-eared mouse. These mice have somehow overcome the Monarchs' chemical defenses enough to use them as an important food source during the winter.
References:
Journey North
Henderson State University
Science Friday
Photography Credit:
Lincoln Brower
Lyndsay Nicole is a contributor to this page and the forthcoming Fly Monarca documentary film.
