Plebejus acmon acmon

Acmon Blue

Plebejus acmon acmon is a small blue that flies much of the year in many of the places one may go to look for butterflies in southern California, from the coast up into the mountains. That's in large part due to the many hosts it can utilize. These include several common buckwheats, and members of the pea (legume) family including lotus plants, vetches, and clovers. A butterfly that can use both deerweed and California buckwheat is going to do well here. I've read that in coastal areas, with favorable conditions, acmon may have as many as 5-6 broods in a single year.

Acmon overwinters as a pupa. When these overwintered adults emerge (often in February-March), females should be of form "cottlei": blue on the dorsal side, whereas they will be brown in the later generations (with a yellow-orange aurora on the hindwings above). According to Paul Opler, overwintered males of this early brood "are characterized by a more grayish appearance below, more blackish scaling above, and a deeper shade of blue" ("Fixation of Type Locality for Lycaena acmon Westwood and Characterization of the Species and its Distribution," Taxonomic Report 4:1 (Mar.1, 2003), p.2). This may not always hold true; some males that I've seen early are typical of later broods, when acmon males are a bright lilac blue with a pinkish to salmon-colored aurora on the hind wings above, as in the first photo below.

What we now call Plebejus acmon acmon was collected by Pierre Lorquin early in his visit to California during the gold rush, probably around San Francisco ca. 1850. He sent specimens to Boisduval in France, who included a description of this butterfly in an 1852 paper. However, an illustration of a male acmon was published in Westwood and Hewitson's Genera of Diurnal Lepidoptera earlier that year. That specimen - now in London's Natural History Museum - may have been sent by Lorquin to London as well. Had Boisduval published his description before Westwood, this butterfly would now be his species "antaegon".

Plebejus acmon - Acmon Blue
This is a typical male Acmon Blue, Plebejus acmon acmon, nearly identical to the type specimen. From San Gabriel Canyon, March 8, 2006.
Plebejus acmon - Acmon Blue type specimen illustration
William C. Hewitson painted this butterfly ca. 1851, when it was new to science, for the two-volume work, The Genera of Diurnal Lepidoptera.
Plebejus acmon - Acmon Blue original description by Westwood
And here's the original description - such as it is - of acmon (#139) in the list of butterflies of the genus Lycaena by John O. Westwood in the same volume, referring to Hewitson's illustration, with a Type Locality given simply as "California" and noting its deposition in the British Museum.
Plebejus acmon - Acmon Blue
This female was in the same side canyon (Islip Canyon) of main San Gabriel Canyon as the Acmon male above. These early females are form cottlei. March 14, 2006.
Plebejus acmon - Acmon Blue
Female Acmon Blue later in the year, not yet completely brown. Malibu Creek, June 28, 2005.
Plebejus acmon - Acmon Blue
Same place as above but in September; this female acmon is all brown on the dorsal side. Malibu Creek, Sept. 15, 2005.
Plebejus acmon - Acmon Blue
Ventral of the Acmon Blue, Pt Mugu State Park, Santa Monica Mountains, August 20, 2005.
Plebejus acmon - Acmon Blue
One more ventral Acmon Blue. Bear Canyon in the Cleveland NF off the Ortega Hwy, August 10, 2005.
Plebejus acmon - Acmon Blue
Larva of Plebejus acmom acmon on Eriogonum davidsonii at Cactus Spring Trail. May 29, 2016.
Plebejus acmon - Acmon Blue
Closer look at the one above.
Plebejus acmon - Acmon Blue
Here's the entire plate from the book in which acmon was described over 160 years ago.

©Dennis Walker