Great Purple Hairstreaks in Sonoma County

Sonoma County-- like most of America between the 45th parallel and the Darian Gap--is properly territory for Great Purple Hairstreaks; but they are rarely seen here. As I understand it, that's usual for this insect. They are probably rather common, but remain unseen as they live out their lives in the canopy where their host mistletoes lives. We are invited to look for a flash of their brilliant blue upper wings as they flit among the treetops... I still hope to see this!
Five years ago David Rawlinson asked me about seeing one in Sonoma. I'd not, so I resolved to look.
At that time, the only contemporary record I found was a photo on the Website of the Hallberg Butterfly Garden in Graton. Evidently not a fluke, as Alex Weishaar saw one there since.

Since then, I had no personal success with this project. But we can see a few observations trickling in since:
Fountaingrove 4/16 (A Wight)
Pepperwood 5/17 (W. Herniman)
Rincon Park 7/17 ( 'Christine 21')
Hood Mountain 3/18 (D. Loarie)
Unfortunately, there's no pattern here to guide us: aside from returning to the general location of a serendipitous find.. David had suggested a strategy of checking Coyote Brush in bloom, where he'd seen one in Novato . This is on the short list of flowers that seem to regularly tempt our GPH; an attraction that must be all the more compelling in the floral desert of late September. Since I already made a practice of visiting every flowering Baccaris for a dozen other species, it was easy to follow this advice. Further good council would have been to put aside any expectations that might spoil an otherwise satisfactory visit to a promising site. Not today! Try to be worthy!

Finally, last year Brian Reed found one on a solitary large bush near the water treatment pond where Santa Rosa Creek joins the Laguna de la Santa Rosa. He resolved to monitor the spot this year, and finally saw another 9/23. He generously texted a few other frequent creek visitors, and the game was on!

It wound up requiring a few visits, but not a minute of this was wasted. This large female bush throbbed with the resonanting wingbeats of thousands of bees, wasps, flies butterflies, moths and the occasional small bird. Like most years, we saw nice Purplish Coppers here, scores of Grey Hairstreaks, and 14 other butterfly species on or around the bush. You'd expect October butterflies to be a bit worn like the resident skippers, some hardly identifiable. But others were fresh and immaculate, especially the Mylitta Crescents, Buckeyes and Grey Hairstreaks. Some of the later quite dark, and for a heartbeat much like a Great Purple Hairstreak. One Buckeye was a full 'rosa' form: this alone worth a special trip.

Ultimately one of the dark butterflies proved to be the right kind. This was clearly not Brian's butterfly, which had been damaged, but an immaculate imago. A startling creature , now velvety black, then turning slightly in the glare to assume that dull purplish hue that led to the name. Flitting in and out of the foliage from dark to light, this lovely flat black creature is very challenging to photograph. Over the next few days a succession of visitors did their best as their subject would spend hours hopping around the top of the bush. Despite our best efforts, nobody ever saw which way it flew off after nectaring. Adjacent Willows on the creek are laden with mistletoe, and I'd hoped that might be the location of a colony, but we saw nothing to support that idea.

One nice observation allowed by these prolonged visits was appreciation of the hindwing structures that lend a 'false head' appearance on' top' of these often long- sitting and downward-facing butterflies.

Such are common to all the Hairstreaks, thought to be a subterfuge to draw bird strikes to an expendible scrap of wing. Or just ornamental? In GPH, these are especially well developed, and lend credence to the proposition that they are lures.

Probably best of all was the unexpected pleasure of sharing the joy with a succession of fellow enthusiasts. We get this at the occasional Butterfly Count, but it rarely happens in the bush. On my second day there was a troop of Birders streaming by to see Bald Eagles 1/2 mile up the trail. Seven of us remained by our Hairstreak with only a distant sight of these noble birds. Eagle or Butterfly? On occasion, one must choose; so it was nice to have company.

Posted on October 8, 2021 01:09 AM by icosahedron