This looks like a fly, but acted like a bee. They were around a lavender bush in our yard
These wasps have built mud dwellings in the spaces between the bricks on the facade of our house. The entry can be seen in the photo.
20 + individuals (adults) found in restored grassland. Courtship observed. Healthy population at Horse Park Woodside (private). No diagnostic photo - sorry :(
10 + individuals and restored grassland. Courtship observed
Calathus ruficollis (Carabidae, ground beetle), Redwood City, San Mateo County, California - 27 November 2010. Thanks to v belov and Bug Guide for the species-level identification: bugguide.net/node/view/475550 Appears to be quite common in the Bay Area.