Searching host plants for immature butterfly stages can be a fun pastime while waiting for spring flight season. Sometimes, even finding the host plant can be a challenge.
Dicentra uniflora is a plant that can often go unnoticed in sage steppe habitat. It emerges soon after snow melt and is quite small. Photos of it often include a coin to highlight how small it really is (Figure 1). One look at this uniquely beautiful flower confirms how its common name, Steer’s Head, came to be. The entire plant senesces and essentially disappears fairly quickly before adults fly, further complicating locating it. Why the interest? It was assumed that Steer’s Head was the host plant for the Clodius Parnassian, Parnassus clodius, east of the Cascades in Washington state, though not confirmed.
I observed P. clodius at my residence in Winthrop, WA, the last several years. A freshly mated female was observed in my front yard (Figure 2, note the white sphragis at the abdomen tip) May 22, 2019, indicating close host plant proximity. Reporting this observation to Jonathan Pelham resulted in his prompting me with, Where’s the host plant? I’d not seen Steer’s Head at my home, but knew it’s a beauty found in the Methow Valley often cited as blooming in May. I began looking around my home in earnest in 2019, but found no plants that summer, nor the next.
The early bird gets the worm. In 2021, I started looking in February while a good portion of the hillslopes were covered in snow. On March 20, 2021, Steer’s Head plants were observed on the sun-exposed, east-facing hillslopes amongst the rocks, bitterbrush and sage (Figure 1). Of note, as of this date even the presumed earliest bloomers, Spring Beauties and Yellow Bells were yet to bloom. Over the next few days the Steer’s Head appeared in large numbers as the snow continued melting and the soil warmed. Notably, those areas with highest solar gain and protection were first to show emergence. The close proximity to my residence made multiple daily forays convenient. On hands and knees I spotted one plant with nibbled leaves and that evening I went out several times to search for the crepuscular caterpillar per James and Nunnallee (2017). None were seen. Finally at 9:30 AM, March 25th, a P. clodius caterpillar was seen warming itself in the sun near the nibbled Steer’s Head (Figure 3). The first few days after finding the nibbled plant, I continued looking periodically at night. But after several daytime sightings of caterpillars, I gave up on the cold evening explorations. Over the next few weeks, 4-5 individuals were observed feeding in the same location until early April (Figure 4). All feeding observations were during the day from approximately 10 AM to 4 PM. I suspect the late evening to early morning temperatures being below freezing must send them burrowing for cover. They likely return to the surface to bask in the early morning sun to warm themselves prior to feeding. From 8:30 -10 AM they were typically stationary, likely warming themselves in those protected sunny places. One larva was seen in late afternoon burrowed into the adjacent leaf litter, it’s posterior end just barely visible. Family obligations curtailed observations for a few weeks and upon my return in early May, many plants in the vicinity of where P. clodius had been observed had already senesced. The first P. clodius adult in 2021 was seen flying down our lane May 10; how fun to confirm they are residents.
Reference
James, D.G. and D Nunnallee. 2011. Life Histories of Cascadia Butterflies. Corvallis: Oregon State University Press.
All photos by Cheryl Bellin.