July 26 Irruption of California Tortoiseshell

[Dale Hoyt]

Just returned from a vacation to Northern California. Sorry this is so 
late. We were at Mt. Lassen National Park on Thursday, July 26 and started 
climbing Mt. Lassen in the morning. We reached the summit about 11:30 and I 
noticed a number of California Tortoiseshells (Nymphalis californica) 
flying up and over the summit. These started to increase in number as we 
sat and chatted with other hikers and I thought I was seeing a good example 
of hill-topping. Around noon we started back down and now the 
Tortoiseshells were really abundant -- strings of a dozen or more flew by 
our heads every few minutes and I thought that this was extraordinary! 
Extraordinary turned out to be an understatement. As the trail descends 
from the summit it passes through a huge scree field (talus slope) that 
stretches down perhaps 500-1000 feet from an altitude of about 10000 feet. 
This field occupies nearly the entire SW side of the mountain. At the end 
of the first switchback we looked down this slope and saw Tortoiseshells 
covering literally every square foot of the scree field. All were flying 
about 1-2 feet above the surface and headed upward! To say there were 
thousands of butterflies is perhaps conservative. We stood and watched as 
hundreds passed near us every minute. They were so dense that some actually 
flew into us and bounced off! I've never seen such a concentration of 
butterflies in my life.
         In all this activity I never observed a mating pair. Was this 
because mating takes place later in the day? I looked for pairs in the 
rocks, but didn't see any. I wasn't able to determine the sex of the 
butterflies, either. Sorry I couldn't get access to a computer sooner to 
let you all know -- this was a sight not to be missed.

Cheers!

Dale Hoyt


 
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