Discover magazine reveals a grisly bit of previously unknown insect behavior recorded by Yi-Kai Tea and his fellow citizen scientists on the island of Sulawesi, where they photographed innocuous-looking milkweed butterflies feeding on the bodily juices of caterpillars:
This kind of butterfly vampirism was a wholly new observation, says Tea. He studies coral reef fish in his day job as a research associate at the Australian Museum Research Institute and PhD candidate at the University of Sydney. Tea is also a passionate amateur naturalist, and he loves finding and photographing butterflies.
Milkweed butterflies, a family that includes the iconic monarch, are known to scratch at and drink from plants that contain chemical compounds necessary for their survival. But butterflies feeding on living creatures, not to mention caterpillars from closely-related species, was something surprising.
Far from being an isolated incident, they found butterflies attacking and imbibing from caterpillars in photograph after photograph. All told, they found seven species of milkweed butterfly going after caterpillars from a few different species in the milkweed butterfly family. Their find was significant enough that they partnered with two other naturalists to document their find in a scientific paper, published in September in the journal Ecology.
In the paper, Tea and his co-authors suggest a name for the behavior: kleptopharmacophagy. “Klepto” means “to steal” from the ancient Greek, while pharmacophagy is a term for when animals eat things for their chemical contents, rather than for nutrition.
The butterflies were most likely after compounds known as pyrrolizidine alkaloids, made originally by plants. The toxic chemicals are a dietary staple for caterpillars and butterflies alike, giving them an important chemical defence against predators.
“This is why milkweed butterflies (like the monarch) are so colourful, yet fly in such a nonchalant devil-may-care manner,” Tea says. “They rely on these toxins for protection, and advertise them with their warning colors.”
“Caterpillars, particularly milkweed caterpillars, are just bags of macerated leaves — in this case, the same leaves that contain the alkaloids the butterflies seek,” he says. Combined with the caterpillars’ thin skin, it could make them a tempting target for milkweed butterflies in search of an alkaloid boost.