One of the best spots to enjoy gorgeous butterflies in their natural habitat is the remarkable Chesapeake and Ohio Canal. Along this 184 mile refuge amidst the paw paws, tulip trees, sycamores, and cherries, zebra swallowtails, eastern tigers, and many other ethereal beauties zoom and glide along the towpath in search of food and mates.
When I think of butterflies, the image is one of flowers, fluttering wings, and a busy proboscis probing corollas to obtain carbohydrate rich nectar, the fuel that powers the flight muscles of these restless pollinators. On a recent visit to the C & O, I was surprised to see a gaggle of eastern tigers clustered on the muddy riverbank busily engaged in a food fest. A closer look revealed the object of their smorgasbord to be the carcass of a large dead fish. Nearby, a spectacular zebra swallowtail busied itself in the mire. Why do these winged beauties feed on seemingly nasty tucker like dead fish and mud?
Not far from the fish foraging tiger swallowtails a beautiful zebra swallowtail probes the mud for nutrients.
The answer lies in the nutritional needs of the long lived butterflies. For many Lepidoptera, members of the moth and butterfly clan, a lifetime’s worth of nutrition is gathered during the larval stage when caterpillars feast on nutrient rich leaves of plants. Many moths like Royal Walnut Moths and Imperial Moths, which we met in previous episodes, never feed as adults by virtue of their feeding efficiency as larvae. For many moths life is ephemeral, consisting of a brief interlude with a mate, depositing a full complement of eggs on a host plant, followed by a swift demise, often at the beaks of feathered predators.
By contrast, many butterflies live for relatively long periods of time, intervals measured in weeks and even months. In addition to energy packed carbohydrates needed for flight, long-lived butterflies require the building blocks of proteins, amino acids, and critical elements, particularly sodium, to conduct the biochemical business of life. These nutrients are found in myriad sources including the mineral rich mud, decomposing flesh of fish, or deposits of scat left behind by raccoons and other small mammals along the banks of the mighty Potomac.
In some cases, nutrients such as sodium are passed along with the sperm of the male butterfly to the female at the time of mating. This nuptial gift may boost the survival of the lucky couple’s eggs. When crowds of butterflies are observed “puddling”, as this non-nectar feeding behavior is dubbed, it is not unusual for the gang to be comprised mostly of males as they collect nutrients to woo their mates. In the world of these long-lived beauties, it appears that butterflies cannot live by nectar alone.
Vital minerals found in soil are lapped-up by this painted lady.
Bug of the week thanks Eloise and Ada for providing inspiration for this episode. The interesting article, “Mating systems and sexual division of foraging effort affect puddling behavior in butterflies” by Collen Scully and Carol Boggs was used as a reference for this episode.