24 spp. in 4 subgenera in our area, 351 spp. in 22 subgenera worldwide(1)
Subgenus not yet in the guide is Euceratina
(a palaearctic group, with a single adventive species in our area, 38 spp. total)(1)
The easiest method of separating Ceratina from Xylocopa is by size: Ceratina are under 8 mm in length whereas Xylocopa are 20 mm or larger. In addition, Ceratina has the second submarginal cell about as high as wide basally, whereas in Xylocopa it is about half as high as wide basally.
According to(2) C. (Zadontomerus) dupla
may serve as an example: Body bluish green, clypeus with oblong, median maculation; antennae brownish basally, spurs pale yellow. Adults visit raspberry and goldenrod flowers particularly but also many others. They nest in sumac and elder stems.
Features that help with ID of this genus : club-shaped abdomen, dull metallic color and inconspicuous hair. Males have larger white markings on the face. (Eric Eaton)
The clublike abdomen
narrows to an abrupt point (3)
They excavate nests with their mandibles in the pith of broken or burned plant twigs and stems. Females overwinter as adults in partially or completely excavated stems. In the spring, this resting place (hibernaculum) is modified into a brood nest by further excavation.