Western Tiger Swallowtails

The "outbreak" of Western Tiger Swallowtails has continued for a second year. Elevated populations are reported at least as far east as Reno and as far west as Fairfield and Vallejo. The "epicenter" seems to be in Davis, however, where it has been on the wing every week since the last week of March, with no clear break between generations (very unusual), and at times in certain neighborhoods (e.g., College Park) one could see 5 or 6 individuals at one time. The phenomenon has attracted a lot of interest from the general public, which is unsurprising--and no, we don't have an explanation for it! (Wish we did.)