Wildlife and Other Sightings: Robber Fly & Bumble Bee, plus the Tuolumne Area Butterfly Count

August 18, 2012 Posted by: BW – Mather District Volunteer Interpretive Ranger

Robber Fly and Bumble Bee
Family Asilidae and Bombus sp.
Robber Fly vs. Bumble Bee

July 29, 2012

This little drama was seen playing out on the Yosemite Creek Trail last week. A robber fly and a bumble bee were wrestling in the trail. The robber fly preys on other insects, usually attacking in the air. Long strong legs, lined with stiff hairs, allow the robber fly to form a cage around its prey, making escape very difficult. After it has captured prey, the robber fly injects it with saliva filled with enzymes that paralyze and digest the bodily contents. This robber fly soon had access to a bumble bee smoothie for lunch!  

Tuolumne Area Butterfly Count
Checkerspot  Female Melissa Blue

Fritillaries on Asteracae  Lustrous Copper

Small Wood Nymphs

July 30, 2012

A group of dedicated local naturalists recently headed out into Yosemite with binoculars and butterfly books. They were counting alpine butterflies in and around the Tuolumne area. The count, which was registered with the North American Butterfly Association (NABA), was a compilation of all butterflies observed at sites within a 15-mile diameter count circle in a one-day period. The count circle for Yosemite was centered on the Tioga Pass, which allowed for counting butterflies on both the east and west side of the Sierra Nevada Mountains. NABA analyzes the data collected during these counts and publishes an annual report that provides a tremendous amount of information about the geographical distribution and relative population sizes of the species counted. Last year there were 427 counts across the United States.  

Most of the butterflies seen in Yosemite were Blues, Fritillaries, and Coppers, but 46 species total were identified during the count. Pictured butterflies from the count are:

Checkerspot (Euphydryas sp.) - top left
Melissa Blue (Lycaeides melissa) - top right
Fritillary (Speyeria sp.) - middle left
Lustrous Copper (Lycaena cupreus) - middle right
Small Wood Nymph (Cercyonis oetus) - bottom


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