The other day, I was thinking about the feasibility of feeding butterflies buttered flies and, long story short, I was met with the disappointing discovery that there are in fact no strictly carnivorous butterflies. In part, this is due to the fact that, for many species, the butterfly stage of the life cycle is almost entirely focused on reproduction.
It’s analogous to the years following puberty in humans (otherwise known as college). However, there is such a thing as a carnivorous caterpillar, though they don’t eat flies.
I admit I wasn’t always friendly to caterpillars as a kid. They used to build their nests high up in the trees in front of my house, spilling hundreds of the little wrigglers onto our lawn. I was appalled.
My eight-year-old sensibilities told me there was nothing to find but fear in those great masses of writhing bodies. However, if there is anything I can do to make up for my past injustices, it would be to dispel the ignorance surrounding our squishy little friends.
Within the second largest family of butterflies, Lycaenidae, there is a subfamily of rare caterpillars that make up less than one percent of all butterfly species. This subfamily is called Miletinae, and the caterpillars within it have adapted a unique way to sustain themselves which involves a heart-breaking evolutionary betrayal as well as chemical subterfuge.
But let’s start at the beginning. Lycaenidae butterflies, sometimes called gossamer-winged butterflies are known for a few things. Their metallic glossiness, their flat looking larvae and their close association with ants. About 75 percent of the family have some kind of relationship with the hardworking insects.
For some species, the ants actually protect the larvae, in return receiving a sugar-rich honeydew (which is also secreted by aphids, fun fact) from them. With others, the ants will continue protecting the pupa as well.
This means that the post-metamorphosis butterfly actually emerges from an ants nest as well as a cocoon.
Scientists believe that it is through this mutualism that Miletinae butterflies were able to develop their parasitism. It’s basically the evolutionary equivalent of stabbing your best friend in the back… and then eating them.
Lycaenidae butterflies are the proud owners of a tentacular organ. It’s cylindrical, topped with spikes, eversible and believed to be the reason that this particular family has such a close association with ants. The organ emits chemical signals that researchers believe help the larva communicate across species boundaries.
Capitalizing on this ability, Miletinae caterpillars cloak themselves using chemical signals which mimic those of the aphid, which ants are drawn to for the honeydew. This means that the caterpillar can be left to live among their prey. It helps that they will often tie, using silk excretions, the dead carcasses of consumed aphids onto their bodies, which helps them to camouflage as well.
And things don’t get much better for the ants once the caterpillars leave the nest. Unlike most butterflies, those belonging to the Miletinae subfamily forgo plant nectars, instead partaking in the honeydew secreted by aphids, which their larva feed on as well. However, they will also feed from mineral rich sources such as mushrooms, sap or even mud.
Their carnivorous tendencies are likely why these caterpillars are often referred to as the harvester subfamily. A cool name to match some cool caterpillars.
If I can’t convince you that caterpillars deserve your admiration, perhaps someone you actually respect can. Vladimir Nabokov, the Russian-American novelist, was actually an experienced lepidopterist, a collector of butterflies, and curated the Museum of Comparative Zoology at Harvard University (probably why they’re always beating us in the rankings).