Tigers on Market Street: A Remarkable Story of Adaptation for San Francisco’s Largest Butterfly
A project by Amber Hasselbring and Liam O’Brien
The phenomenon of the Western Tiger Swallowtail (Papilio rutulus) and its behavioral adaptation to Market Street was first noted by lepidopterist Harriet Reinhard in 1987. During the 1960’s and 70’s the London Plane Tree (Platanus X acerifolia) – one of the butterfly’s larval food trees – was planted en masse in the heart of the City. In combination the trees, canyon of tall buildings, dappled sunlight, and the presence of underground water, an unexpected habitat was created. The butterfly’s story is 75% known: males and females fly above the canopy looking for mates, females lay eggs on the leaves, caterpillars feed on foliage and pupate, and adults emerge in spring to repeat the cycle. The butterfly overwinters as pupa attached to tree bark.
Featuring this butterfly’s story could have ramifications for urban planners worldwide. We as a species have a history of changing the natural world too quickly for most creatures to adapt. The uniqueness of a 40-year-old urban forest of London Plane Trees and the presence of this butterfly despite hostile conditions provides a controlled setting for observation. The more we understand about the creatures that have moved in, the better we can provide what’s missing in the unnatural habitat and further mimic their natural habitats.