Milkweed butterflies have been seen for the first time feeding on live caterpillars, the young of their own species. According to researchers, they do this to increase their supply of mating pheromones.
One of the most recent discoveries that raises issues in insect evolutionary theory is a butterfly’s behavior toward members of their own subfamily (Danainae).
In a study published in the Ecology’s The Scientific Naturalist, scientists claim that milkweed butterflies harass, subjugate, and feast on live, dead, and dying larvae belonging to other milkweed butterflies – essentially their own offspring.
The caterpillar marks the larval stage of butterflies and moths.
Caterpillars consume poisonous plants and store toxins as a form of self-defense. These poisonous chemicals act as a repellent towards predators like birds, which are later manifested in the vivid, warning colors of butterflies.
Male butterflies use these molecules to cultivate mating pheromones, which serve as nuptial “gifts” to females as part of courtshipping. Male butterflies enhance their diet by searching for supplementary sources of chemicals to increase their natural toxicity.
These are usually derived from plant sources, but deep within the jungles of North Sulawesi, Indonesia, it appears that they have developed a palate for caterpillars – one that aligns with their pursuit to dilate supply of this love drug.
Yi-Kai (Kai) Tea from the University of Sydney School of Life and Environmental Sciences, said: “The behaviour does not fit neatly in the traditional modes of predation, parasitism, or mutualism, and so presents a new challenge to evolutionary theory. We have coined it ‘kleptopharmacophagy’ – chemical theft for consumption.”
The butterflies partake in a behavior known as “leaf-scratching” to augment the chemical supplies already acquired as caterpillar adolescents. With their sharp tarsal claws, they gnaw at chemical-containing plants to extract plant juices, absorbing them with their long, curly tongues.
Scratching at live caterpillars, on the other hand, had never been documented before. Researchers observed adult male milkweed butterflies that were seen clawing at both the leaves as well as live and dead caterpillars, ingesting their secretions. “The caterpillar larvae would contort their bodies swiftly in vain attempts to stop the scratching,” he explained
“Caterpillars are essentially bags of macerated leaves; the same leaves that contain these potent chemicals the milkweed butterflies seek out. To adult butterflies, they may simply be an alternative source of chemicals on which to feed,”
“The caterpillar larvae would contort their bodies rapidly in what appeared to be futile attempts to deter the scratching,” Mr Tea explained.
While studies have found milkweed butterflies to be consuming on the carcasses of other chemical-containing insects, this is the first evidence of how such behaviour had been carried out by live insects of the same order, specifically their own larvae. However, It’s still unknown whether the caterpillar deaths had a casual relationship linked to the scratching.
These grounds pave more questions about the ecology of these iconic butterflies. Which exact compounds are these butterflies particularly interested in? Is similar conduct common in other parts of the world?
