California Yellowjacket (Vespula sulphurea)

Habits:

California Yellowjackets have not been reported as "picnic pests", but they are attracted to sugary secretions and prey on live insects.

Nests:

Most California Yellowjacket nests are subterranean, but they can also be found in logs and manmade structures. This yellowjacket species is not as abundant as others found in California and surrounding areas. 

Nature toward humans:

California Yellowjackets are not a serious stinging hazard unless the nest is disturbed.

Other Yellowjacket species

Paper Wasps

Hornets