Arthropods
Insects and spiders belong to the Arthropod phyllum- segmented animals with 
exoskeletons, jointed appendages,and no backbone. This is a phyllum with numerous taxa: California as a whole has an estimated 30,000-35,000 species of insect alone.
Yosemite's arthropods can be found anywhere from the bottom of its valley floors to the tops of its mountain peaks. Rare alpine butterflies inhabit elevations of about 3,000 meters (10,000 feet) and above, while the Yosemite cave pseudoscorpion (Parobisium yosemite) dwells in talus caves in Yosemite Valley. Talus caves form when rocks and boulders fall down from cliffs and slopes. The gaps between the fallen rocks become caves that are well-suited to troglobites adapted to dark environments. Scientists came across the Yosemite cave pseudoscorpion by accident during a survey, and it was officially recognized as a new species in 2010. This blind cave-dweller is about a centimeter in length and looks like a scorpion; however, it has no posterior eyes, no tail, and no stinger. It does have a venom-filled claw, but fortunately for us, it is not large enough to harm a human.
More Information:
Garth and Tilden- Yosemite Butterlies (ecological survey from 1963): http://lepidopteraresearchfoundation.org/journals/02/PDF02/02-001.pdf
LiveScience- New 'Pseudoscorpion' Discovered in Cave of Yosemite: http://www.livescience.com/29862-new-pseudoscorpion-discovered-cave-yosemite.html
National Park Service- Alpine Butterflies: http://www.nps.gov/yose/learn/nature/butterflies.htm
National Park Service- Annual Yosemite National Park Butterfly Count: http://www.nps.gov/yose/learn/nature/butterflycount.htm
National Park Service- Insects and Their Relatives: http://www.nps.gov/yose/learn/nature/insects.htm
National Park Service- Pseudoscorpion—Unique to Yosemite: http://www.nps.gov/yose/learn/nature/pseudoscorpion.htm
Powell, J.A. and Hogue, C.L. 1979. California Insects. Berkeley, CA: University of California Press
Yosemite Library- Insects of Yosemite National Park: http://www.yosemite.ca.us/library/handbook_of_yosemite_national_park/insects.html
