Walking on a woods road beside a stream in early July, I spotted several tight clusters of butterflies perched on scat piles and on wet sand near the brook. When one of the butterflies spread its wings, I saw that its topside was black with blue shading, and had a broad white band running through the center of its fore and hindwings, creating a U-shape. Red dots and light blue-and-white dashes decorated the margins of its hindwings. Most of the butterflies had their wings folded together perpendicular to the ground, showing their dark brown undersides with colored dots and dashes similar to those on top.
These attractive butterflies are white admirals (Limenitis arthemis arthemis), a subspecies of the red-spotted admiral butterfly. Although it may seem strange to find such beautiful creatures gathered on scat, this behavior — known as puddling — is common among many butterfly species. Butterflies puddle to replenish fluids and obtain nutrients, especially sodium, essential for reproduction and flight. They take up nutrients with their long, tubular tongues, or proboscises.
Congregating this way makes it easier for females to find mates. Most puddling on salty substances, however, is done by males. They incorporate sodium into the spermatophore, a package containing the sperm, which a male will transfer to a female during mating. Researchers have found that sodium increases egg viability in some butterfly species.
White admirals are notorious puddlers, and also feed on rotting fruit, carrion, sap, and honeydew made by aphids. They are attracted to road salt remaining from winter and to sweat on clothes hanging outdoors. White admirals do not nectar as much as other butterflies do, but do occasionally visit woodland flowers.
This northern forest butterfly ranges across northern New England, New York (where it is the official state butterfly), the Great Lakes states, much of subarctic Canada, and into Alaska. White admirals inhabit conifer and mixed woods, especially along watercourses, clearings, and woodland edges.
In southern Vermont and New Hampshire, the white admiral hybridizes with the red-spotted purple admiral, a subspecies common in southern New England that does not have a white band. In the zone of hybridization, these butterflies often have partial white bands. The red-spotted purple does not have a white band because it has evolved to mimic the poisonous pipevine swallowtail found in its range as a defense against predators.
White admirals fly in our region from late May to early September, but are usually most abundant in late June and early July. Sometimes there is a smaller second generation in August. Look for butterflies that take short flights, staying low to the ground. White admirals also bask in the sun on leaves and gravel roads.
Individuals live only one to three weeks, during which time they must reproduce. Females lay pale green eggs on leaf tips of preferred host trees such as birch, aspen, willow, and cherry. The emergent caterpillars become brown-green with white saddles as they feed on the leaves of these trees. As these caterpillars outgrow their skin, they shed to reveal new skin beneath. White admiral caterpillars go through three of these growth stages, or “instars.” In fall, a third instar caterpillar will attach to a twig on a host tree and make a leafy case around itself. It develops a hard-shelled chrysalis in which to spend the winter. In spring or summer an adult butterfly emerges from the chrysalis, and the cycle begins again.
Susan Shea is a naturalist, writer, and conservationist based in Vermont. Illustration by Adelaide Murphy Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of the New Hampshire Charitable Foundation: nhcf.org.
