Williams, P. H. (2014). Bumble bees of North America: An identification guide. Princeton University Press.
Lua i Stíl Chicago (17ú heag.)Williams, Paul H. Bumble Bees of North America: An Identification Guide. Princeton, New Jersey ; Oxfordshire, England: Princeton University Press, 2014.
Lua MLA (9ú heag.)Williams, Paul H. Bumble Bees of North America: An Identification Guide. Princeton University Press, 2014.
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