Chlorostrymon simaethis sarita

Silver Banded Hairstreak

The larval food plant for this hairstreak is balloon vine, which is not in southern California natively. It does, however, grow naturally in Baja California (perhaps in southern Texas as well). So, why does it occasionally make a surprise appearance so far from its natural habitat? Perhaps it has to do with years of really good rains in Baja triggering a dispersal of this butterfly. 1992 was such a year, and apparently 2017 as well. 2020 has proven to be another year for this butterfly to make an appearnce in both Arizona and southern California in the U.S. Joe Zarki and I found one in Joshua Tree National Park on May 2nd, and I came upon one in the New York Mountains in the Mojave National Preserve just four days later. Once here, this butterfly can establish small colonies around plantings of the host in yards, as has happened for lepidopterists John Emmel and Gordon Pratt. But what is going on in remote areas such as the New Yorks? Is it truly able to fly such amazing distances while remaining in remarkably good shape, or is there a host plant we don't know about sustaining it when balloon vine isn't available?

So, how to develop a plan to find this rarity? I don't know that you can, at least not in southern California. I had ideas, but ultimately I was lucky and it found me. If I were to make whatever trip was necessary at a time there weren't specific reports of decent numbers from Arizona (as there are as I type this), I would probably try to find an established colony in southern Texas. The two I've seen were probably transients stopping to nectar; no reason to believe they are hanging around.