Osmia neartica Rightmyer, Griswold, & Arduser, 2010  

Osmia nearctica is one of two members of the xanthomelana species group in North America; characters to distinguish it from the other member of that group, O. maritima, are given under that species. In the Palearctic, O. nearctica is most similar to O. xanthomelana, but can be differentiated from that species by the following characters: In females, the propodeal triangle is shining but weakly shagreened throughout (O. xanthomelana with entirely polished, strongly shining lower half of the propodeal triangle), the outer hind tibial spur is only about half the length of the hind basitarsal segment (O. xanthomelana with outer hind tibial spur nearly three-fourths length of hind basitarsal segment), and the lower margin of the mandible has a distinct, translucent flange that curves away from the condylar ridge (O. xanthomelana with the lower margin of the mandible opaque, forming a ridge that is parallel to the condylar ridge). The hairs of the mesepisternum tend to be dark brown in O. nearctica, while in O. xanthomelana the hairs tend to be pale yellow to white, and the hairs of the hypostomal area tend to be denser in O. nearctica than in O. xanthomelana. In males, the propodeal triangle is weakly shagreened throughout in O. nearctica (O. xanthomelana with entirely polished, strongly shining lower half of the propodeal triangle); the lower tooth of the mandible is only slightly longer than the upper tooth in O. nearctica (in O. xanthomelana the lower tooth of the mandible is much longer than the upper tooth and the entire apical margin of the mandible is conspicuously wider than the middle, approaching the look of male Acanthosmioides); T7 midapically has a shallower emargination in O. nearctica than in O. xanthomelana; the S6 midapical truncation is clearly emarginate in O. nearctica (O. xanthomelana with S6 truncation not emarginate); and the apical tip of the gonoforceps (apical to subapical swelling) is more rounded in O. nearctica (in O. xanthomelana the apical tip is more pointed). Osmia nearctica can be differentiated from O. maritima and O. alticola by the microscopic hairs on the underside of the flagellar segments (O. maritima and O. alticola with conspicuous hairs about half the width of the flagellar segments).