However, none of them makes the entire trip. Instead, they lay their eggs and die along the way. The new monarchs that hatch develop into adults and then continue the journey. These monarchs typically live only about two months in total, at which point they lay their eggs and die. This continues until August, when the members of the current generation, none of which has ever seen the fir forest in Mexico, make the trip back there. Individuals often end up landing on the same tree in which their forefathers spent the winter!2 How do these intrepid travelers know where to go? That matter is still under investigation.
It turns out that this migration is just one of the marvels of the monarch. Current research indicates that monarch mothers are also able to medicate their offspring!
Monarchs can be infected by a single-celled parasite called Ophryocystis elektroscirrha. If a female caterpillar is infected, her offspring will be infected if she matures, mates, and lays eggs. This infection can kill the offspring, and even if the offspring survive, they will have problems flying and will have a shortened lifespan.
Thierry Lefèvre and colleagues decided to look at adult females who were infected by the parasite and compare their egg-laying behavior to those that were not infected. One aspect of the egg-laying behavior turned out to be astounding: infected females were significantly more likely to lay their eggs on a specific species of milkweed plant, while uninfected females showed no preference.3
What is special about the specific species of milkweed that the infected females preferred? It contains high concentrations of poisonous chemicals called cardenolides. These chemicals are harmless to the caterpillars that hatch from the monarch eggs, but they make the caterpillars toxic to most of their predators, even once the caterpillars have matured into adults. While uninfected monarch mothers did not preferentially lay their eggs on the milkweed species with high levels of cardenolides, infected mothers did.
Why? Well, it turns out that the cardenolides help fight the infection of the Ophryocystis elektroscirrha parasite. They don’t necessarily get rid of the infection entirely, but they definitely make it less severe, which means the infected mother’s offspring will be healthier than if the mother had laid her eggs on a species of milkweed without high levels of cardenolides. In other words, the mother somehow knows that her offspring are in danger because of her infection, and she chooses to lay her eggs on a plant that will lessen the danger.
What is truly amazing about this result is that the mother gains no benefit from this behavior – only the offspring benefit. Also, since uninfected mothers showed no preference, this is clearly a behavior that has to be triggered by the infection. If the mother is infected, she selects a plant that will combat the infection in her offspring. If the mother is not infected, she doesn’t bother to select a specific plant.
There hasn’t been an enormous amount of research into the subject of how and when animals use medicine in an attempt to heal themselves or their offspring. Hopefully, studies like this one will encourage more research on this fascinating topic. I personally think that there are probably many, many examples of this in creation, as the Creator’s ingenuity is truly astounding. We are only beginning to scratch the surface of His incredible works!
1. Robert Michael Pyle, National Audubon Society Field Guide to North American Butterflies, Alfred A. Knopf, pp. 712-713, 1981
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2. Jules H. Poirier, From Darkness to Light to Flight: Monarch-the Miracle Butterfly, Institute for Creation Research, p. 13, 1995
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