• Sutro Stewards

Rare Sighting of the Pale Tiger Swallowtail on Mount Sutro

By: Liam O’Brien


We are so excited to announce a rare sighting of the Pale Tiger Swallowtail on Mount Sutro on May 24th, 2020! Read about the chance encounter below.



The Pale Tiger Swallowtail (Papilio eurymedon) Is not known from our county (We only have three Swallowtails in SF - Anise, Pipevine & Western Tiger) but thrives on San Bruno Mountain. Antidotal sightings in McLaren Park over the years but unlike it’s cousin, the Western Tiger Swallowtail (Papilio rutulus) it is not known to penetrate the urban jungle. Note the thick, vertical black stripes on this species. Western Tigers are much thinner. The ever-so-slight yellow color overall her makes it a girl. 

First personal sighting of this species in our county in 20 years of butterflying. A vagrant? Not sure. Awfully deep into our county being at Sutro. Her host plant, ceanothus, is all over up there and the Pale Tiger is a strong “hill-topper” ( a butterfly mating behavior ) so locale was correct. More questions than answers. But sometimes just...take a breathe and...share a cool thing with other Naturalists. Ps: first sighting of it against the Historic Record since 1910’s - over 100 years! Thanks Matt Zlatunich!

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Sutro Stewards is a project of the San Francisco Parks Alliance, a 501(c)3 California nonprofit public benefit corporation.