Arsenic is toxic to most multicellular life. But caterpillars of one species happily dine on arsenic-loaded leaves, even as their bodies accrue astonishing levels.
Benjamin Jaffe at the University of Wisconsin-Madison got an inkling of the unusual diet while studying a fern called ladder brake that can take up a lot of arsenic from the soil.
While examining the plants in Florida, he unexpectedly found the caterpillars of the moth Callopistria floridensis devouring them. He聽chemically analysed the caterpillars, which revealed they had聽levels of arsenic in聽their bodies several orders of magnitude higher than that he thought would prove fatal.
Advertisement
In the lab, Jaffe and his colleagues grew the ferns exposing them to arsenic in their water. The team then fed fern moth caterpillars on a high-arsenic ladder brake diet, and measured the arsenic levels in their bodies as they grew and developed.
The results confirmed that the caterpillars store arsenic at concentrations even higher than their food source.
鈥淎rsenic has been the foundation of insecticides and poisons for hundreds of years, it鈥檚 the king of poisons and the poison of kings,鈥� says Jaffe.
This ability to eat and accumulate arsenic without dying is unusual, especially for a land-dwelling insect. There have been instances of aquatic invertebrates tolerating high levels of environmental arsenic, but the caterpillars are the only terrestrial animals known to hyperaccumulate the stuff.
But why take on such a dangerous dinner at all? Jaffe thinks the arsenic might make a useful defense.
鈥淭he caterpillars come in many different color morphs,鈥� says Jaffe. 鈥淎rsenic consumption could be driving the variation we see in caterpillar color, which could then be signaling to potential predators that they are poisonous.鈥�
Arsenic might also ward off pathogens, or protect against some other environmental stressor, says Jaffe.
Ecological Entomology
