Butterflies are mostly herbivores and the caterpillars are their main source of food. Caterpillars are the larvae of butterflies and moths, both in the butterfly family of Lepidoptera. Butterflies commonly eat nectar from flowers and drink juices from plant sap, and suck minerals from corpses, but milkweed butterflies are said to eat caterpillars.

Adult butterflies feed on nectar from flowers using their long straw-like tongues for sucking up the liquid. They also drink juices from fermenting fruit, tree sap, and even mud puddles. Some species feed on dung, carrion, or decaying fungi as well.

Are butterflies cannibals?

It’s true that many caterpillars and adult butterflies are voracious meat-eaters. However, these species usually eat dead bugs or insects that have already died from disease. Milkweed butterflies — the same subfamily that includes the regal monarch — are vicious cannibals, latching onto caterpillars and brutally sucking the guts out of them.

Still, cannibalism isn’t actually that common in most butterfly species. In fact, scientists reported just 16 documented cases of carnivorous behavior in North American and European butterflies between 1748 to 2015. That makes up about 0.007 percent of roughly 20,000 butterfly species globally! And if you include only caterpillar-eating insects like mantises or flies (which aren’t technically butterflies), then it’s less than 0.003 percent.

Most caterpillars feed exclusively on leaves for their entire lives as caterpillars, so why do some butterfly species have a taste for flesh? “Cannibalism may be a way to supplement nutrients lacking in their diet,” explains Sarah Fuss, an ecologist at California State University Channel Islands who has studied Monarch Butterfly cannibalism. The monarch butterfly is famous for its reliance on milkweed leaves during its lar.

Milkweed Butterflies Eat Caterpillars

Adult butterflies are known to frequently feed on liquids, including nectar from flowers and tree sap. But scientists didn’t know of any butterfly species that was known to eat the liquid on caterpillars — which is actually known as frass.

However, researchers in Indonesia recently observed an adult male orange-spotted tiger (Milkweed butterfly) butterfly drinking liquid excreted by a caterpillar. When they took a closer look, they found that the butterfly was scraping the caterpillar skin with its front legs and then licking up the liquid that came out with its tongue.

This behavior was first recorded in tsetse fly in 1936, but it has never been seen among butterflies before — or any other members of the Lepidoptera order, for that matter. It is called gastrophilous aphrodisiac foraging behavior.

The research team took this further by creating experiments to see if the catalepsy-like state of the caterpillars had any influence on this feeding behavior. They also explored whether feeding on frass affected the mating success of males and their ability to find females and lay eggs.

Milkweed butterflies

Danainae is a subfamily of the Nymphalidae family of brush-footed butterflies. It includes the Danaidae or milkweed butterflies that lay their eggs on different varieties of milkweed and the clearwing butterflies, and the tellervini. There are 300 species of Danainae found all over the world.

Many species of this subfamily are brightly coloured with orange markings as warning colors. This is because they feed on milkweeds, which contain cardenolides (steroidal glycosides), and are unpalatable to most animals.

The caterpillars are known to sequester these chemicals. The adults may also retain them in their bodies and so gain aposematic coloration. However, some species have lost their ability to utilize these chemicals for protection and therefore appear less vivid in coloring, such as Danaus Chrysippus.

According to research, oracle and monarch butterflies do eat caterpillars. We can assume that other butterfly species do as well. Eating caterpillars is a means of survival for butterflies and helps them grow stronger so they can continue living. In order to consume caterpillars, butterflies have to store the proteins from their meal in their body as fat.

The protein is then manipulated into amino acids that allow the butterfly’s body to grow and produce enzymes and hormones. The caterpillar is better able to survive the transition from moth larva to pupa (cocoon).