“In late July to early August 2004, a swarm of Tortoiseshells 40 to 50 miles long by 15 miles wide traveled south along the Sierra Nevadas,” the National Park Service noted.
The park service asks visitors to take it slow to see and protect the butterfly migration.
“In the event you are lucky enough to witness a population explosion or mass migration, you can enjoy the sight and protect the butterflies by traveling under 30 mph. A slower speed allows the butterflies to drift over your vehicle instead of decorating your vehicle’s grill or adding a large, yellow splat to your windshield.”
A swarm of insects is not often positive news, but scientists say this is nothing to worry about. “It’s not a problem. It’s not, you know, strange. But it’s impressive, and it’s cool to see,” University of Nevada biologist Matthew Forister told SFGATE.
The butterflies will soon begin a new stage.