Plebulina emigdionis

San Emigdio Blue

The San Emigdio blue flies in small colonies despite having an abundant source of larval food plants*. The main plant is the common Atriplex canescens (hoary or four winged saltbush), but it also uses Atriplex torreyi and A. polycarpa. Caterpillars are ant attended, and the presence of Formica francouri seems to be crucial for the presence of the butterfly, quite possibly as a stimulant to oviposition. The presence of certain scale insects and aphids, which also produce fluid treats for the ants, may also be important, and perhaps what keeps the ants present at the saltbushes. If the female butterflies are picking up stimulatory signals from the ants, and not just the plants as would be expected, and if the ants are generally only interested in saltbushes where the scale insects and aphids are, then this helps us understand why there are so many places where saltbush thrives, yet there are only small, scattered colonies of San Emigdio blues around the western Mojave desert. Basically, suitable habitat would be where the ant's distribution overlaps the distribution of the right saltbushes, especially those with certain aphids and scale insects. Such ideal - or necessary - conditions are relatively rare and have a habit of disappearing thanks to human development.

* For much more detail of the life history, habitat, and distribution, see Greg Ballmer's recent paper from 2022, "Life history and ecology of the San Emigdio blue butterfly (Lepidoptera: Lycaenidae)", The Taxonomic Report of the International Lepidoptera Survey 10(9), available online. I've drawn a lot from it for this brief account.

San Emigdio Blue - Plebulina emigdionis
Male San Emigdio blue - Plebulina emigdionis on host Atriplex canescens at Paul's Place, Weldon, Kern Co., CA on April 29, 2008.
San Emigdio Blue - Plebulina emigdionis
A female San Emigdio blue. Same day.
San Emigdio Blue - Plebulina emigdionis
Ventral San Emigdio blue, also at Weldon on April 29, 2008.
San Emigdio Blue - Plebulina emigdionis
I returned to Weldon six years later, on April 20, 2014, and found a few flying at the same spot. Here's a nice male.
San Emigdio Blue - Plebulina emigdionis
A female, same day as above.
Egg of the San Emigdio Blue - Plebulina emigdionis
The immatures here - egg, larva, and pupa - are from Gordon Pratt. This egg was photographed on May 28, 2023.
Caterpillar of the San Emigdio Blue - Plebulina emigdionis
Caterpillar of the San Emigdio blue on host saltbush. July 9, 2023.
Pupa of the San Emigdio Blue - Plebulina emigdionis
And the chrysalis. Also July 9, 2023, at Gordon Pratt's house.
Original description of the San Emigdio Blue - Plebulina emigdionis
This butterfly was first described by Fordyce Grinnell, Jr., in 1905. The journal is Entomological news, and proceedings of the Entomological Section of the Academy of Natural Sciences of Philadelphia.

©Dennis Walker