Owen, Robin E., and Troy L. Whidden. 2013. “Discrimination of the Bumble Bee Species Bombus occidentalis Greene and B. terricola Kirby by Morphometric, Colour and RAPD Variation”. Zootaxa 3608 (5). Auckland, New Zealand:328–344. https://doi.org/10.11646/zootaxa.3608.5.2.