Last week we visited magnificent monarch butterflies as they tanked-up on carbohydrate rich nectar to fuel their royal tasks of locating milkweeds suitable for their young and bestowing eggs on said plants. Fluttering wings and a busy proboscis sipping nectar is a pretty standard image for a butterfly, right? Well, in this episode we take a slightly different look at some of the dietary preferences of these busy pollinators. While all insects, and animals for that matter, require carbohydrates, other critical nutrients including sodium, potassium, and nitrogen are also essential for life. Plants are notoriously low in some nutrients and it is not surprising that several herbivorous insects supplement their plant diet from rather unusual sources. In previous episodes we met tropical butterflies and moths as they gathered on mineral-rich river banks imbibing fluids from salt-laced mud. Closer to home on the banks of the mighty Potomac, we met a gaggle of ghoulish eastern tiger swallowtails gathered to sip nutrient-rich fluids emanating from a decaying fish. Another rich source of nutrients including sodium and nitrogen is dung. We visited the gorgeous rainbow dung beetle and stealthy broad-headed bug as they savored scat, but today we turn our attention to dung-dining by brush-footed butterflies.
Along the Western Maryland Rail Trail’s 22-mile span between Ft. Frederick and Sideling Hill Wildlife Management Area, breathtaking views are matched by the remarkable diversity of wildlife. Recently, somewhere about 4 miles north of Hancock, an unknown vertebrate deposited an impressive pile of dung on the asphalt surface of the trail. Despite the fact that the scat was in an advanced state of decomposition and rather dry, a mixed gang of brush-footed butterflies gathered to enjoy the earthly delights found in the dung. So compelling was this meal that the butterflies refused to yield to passersby on foot or wheel. Beyond the immediate need for nutrients, one more reason for obtaining sodium may underlie the dung feeding behavior of so many butterflies. 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.
Watch as the red-spotted purple and question mark butterflies are joined by pearl crescents, silvery checkerspots, and a hackberry emperor. Wonderful delights dining on dung!
The next few weeks are an excellent time to go for a bike ride or a walk along the Western Maryland Rail Trail and nearby C & O Canal to enjoy what has turned out to be a rather fine season for butterflies.
Bug of the Week thanks Dr. Shrewsbury 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.