For a slightly more technical guide -- but based on easy to see characteristics -- try the key to common wasps and bees of northern California produced by UC Davis:
http://bohart.ucdavis.edu/content/insects/wasp_key.pdf
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The Xerces Society for Invertebrate Conservation
Matthew Shepherd
Director, Pollinator Conservation Program
4828 SE Hawthorne Boulevard, Portland, OR 97215, USA
Tel: 503-232 6639 Fax: 503-233 6794
Email: [log in to unmask]
Web: www.xerces.org
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-- Visit www.honeybeeworld.com/BEE-L for rules, FAQ and  other info ---
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