Oct 11, 2010 09:04 GMT  ·  By

A new research carried out by biologists at Emory University, concluded that monarch butterflies use medicinal plants to treat their offspring for disease.

Monarch butterflies migrate each year from the United States to Mexico and offer spectacular images with the black, white and orange pattern of their wings.

Like for most animals and insects, the monarch butterfly wears bright colors as a way of warning predators that they might be poisonous, and in most cases, this is actually true.

Monarch caterpillars feed on may milkweed plants and some plant species have high levels of cardenolides.

This substance is not harmful for the caterpillars but it is toxic for predators, and it persists even after the caterpillars become butterflies.

Many studies have focused on whether the butterflies chose more toxic species of milkweed on purpose, as a protection from predators, but Jaap de Roode, the evolutionary biologist who led the study, wondered if this had anything to do with the Ophryocystis elektroscirrha.

“We have shown that some species of milkweed, the larva's food plants, can reduce parasite infection in the monarchs,” De Roode said.

“And we have also found that infected female butterflies prefer to lay their eggs on plants that will make their offspring less sick, suggesting that monarchs have evolved the ability to medicate their offspring.”

Ophryocystis elektroscirrha is a parasite that invades the gut of the caterpillars and remain until they become adult monarchs.

The problem is that an infected female will pass the parasite on to her eggs, and if an adult butterfly leaves the pupal stage infected by parasites, it will begin leaking body fluids and will die.

And even if the butterfly survives, it will live less and not fly as well as a healthy one.

What De Roode discovered was that a female infected with the parasite will rather lay her eggs on a toxic species of milkweed.

This is one example of animal self-medication, and according to scientists, this practice is more widespread among animals than we might believe.

De Roode said that these “experiments provide the best evidence to date that animals use medication.”

Thierry Lefevre, a post-doctoral fellow in de Roode's lab, said that “the results are also exciting because the behavior is trans-generational; while the mother is expressing the behavior, only her offspring benefit.

“That finding is surprising for monarch butterflies.”

This study could also benefit human health, according to chemical ecologist Mark Hunter, of the University of Michigan, who worked with De Roode's group on the research.

He says than humans know very little about the potential of plants and that “studying organisms engaged in self-medication gives us a clue as to what compounds might be worth investigating for their potential as human medicines.”

The results of this research were published online in the journal Ecology Letters.