Not all caterpillars become beautiful butterflies. Some turn out to be live cocktails for adults, according to a study in Indonesia. Butterflies scratch the caterpillars, creating wounds from which they then siphon off body fluids and the plant ingredients they contain. This is the first time scientists have documented such behavior in these insects.
Most butterflies of the genus Danaus it feeds on plants containing milk juice, for example, milkweed. Oilseed milk contains toxins, which are then converted into substances that repel predators, as well as pheromones that attract females. Butterflies obtain food from plants by scratching the leaves with their legs.
In late 2019, however, scientists observed that adult individuals living in a nature reserve on the Indonesian island of North Sulawesi found another source of this food: live and dead butterfly caterpillars.
“Kleptopharmacology” in butterflies
According to an article published on September 8 in the journal Ecology, many adults have been spotted scratching the caterpillars along a half-kilometer stretch of coastal vegetation. They then watched the butterflies drink the liquid dripping from the injured caterpillars for hours. The authors of the study added that the butterflies were so busy with their meal that they were not even distracted by human touch.
This behavior had never been documented in butterflies before, and “the caterpillars quickly twisted their bodies in what seemed like vain attempts to stop the nuisance scratching.”
Not everything is clear
Within three days, seven species of butterflies exhibiting this behavior were counted. It is not known whether the dead caterpillars, seen later, died of the wounds themselves, or whether it was the butterflies, sucking the liquid, and led to their death.
As the lead author of the Yi-Kai Tea study from the University of Sydney pointed out, there are many questions about this phenomenon. Among other things, about what specific substances attract butterflies to caterpillars.
According to one possible scenario, the milk sap from plants that accumulates in the bodies of caterpillars makes their body fluids richer in plant components and therefore more attractive.
Main photo source: Jessica Bauman / Shutterstock