On my run today I saw a tiger swallowtail flutter over and land on a roadkilled snapping turtle. The carcass had putrefied and blackened, obviously been dead for several days at least, yet the butterfly landed right on it and began to lap up…whatever it wanted to lap up.
After doing research I found that butterflies reap some sort of chemical from rotting flesh for nutrition. Nature never fails to surprise me. And it never fails to upend my uninformed expectations. Some of us see butterflies as dainty pretty rainbows who only eat the sweet nectar of the flowers they so resemble…but moments like this remind me that butterflies are insects, just like gnats, flies, dung beetles, and other less appealing bugs. And their behavior doesn’t conform to expectations.
My fvery irst iNat observation - the entire reason I joined - was to get an ID for the “Poop butterflies” a coworker and I kept seeing on walks. You can guess why we gave them that name.
I believe in general adult Lepidoptera can feed only on liquid nutrition due to the structure of their proboscis. So besides nectar I have seen them feed on tree sap, rotting fruit, bird poop, dung, compost, carrion (specifically fish), human sweat, damp sand and mud etc. I believe the latter food sources contain certain minerals they would otherwise not be able to intake.
Butterflies are absolutely disgusting. Many tropical species in the Nymphalidae family can be baited with absolutely rotten fish. I once placed a jar of the stuff along a river, and had a dozen species clamouring to get at it within short order. Some Acraea even drowned themselves in the frenzy.
Basically, in dung, carrion, rotten fruit, urine, there are nutrients that the larvae cannot get from their foodplant. So adult males find sources of those nutrients, feed, and then pass them along to the female as a “nuptial gift”. These nutrients are then incorporated in the eggs.
It’s probably worth mentioning the Calyptra moths here as well, aka the “Vampire Moths”, so called because some in the genus drink the blood of mammals.
I recently saw a bunch of swallowtails on some tadpoles in the shallows of a river some of which were marooned. I couldn’t tell if they both were after algae or if the butterflies were trying to eat the dying or maybe dead tadpoles.