The following material taken with permission from: Mitchell, T.B. 1962. Bees of the Eastern United States, Volume II. North Carolina Agricultural Experiment Station. Tech. Bul. No.152, 557 p.
Stelis is a genus of parasitic bees characterized usually by the presence of yellow, ivory or reddish maculations. The scopa is lacking in the females. As in the non-parasitic anthidiine bees, the stigma of the front wing is very short. The scutellum. is rounded; the posterior face of the propodeum is vertical, but there is a narrow, coarsely pitted area along the upper margin that inclines to the horizontal; the mandibles are 3-dentate in both sexes; the mid basitarsi are shorter than their tibiae; and the gonostyli of the male genital armature are abruptly dilated apically, the resulting club strongly angulate. Typical Stelis is an Old World group of species characterized by acutely pointed axillae. In all of the Nearctic species the axillae are rounded.
The subgenus Chelynia has been elevated to generic rank in the Catalog of Hymenoptera (p. 1148) but is being reduced here to subgeneric rank. It is based on Chelynia labiata Provancher, and has been separated from Stelis by the supposed difference in the relation of the second recurrent vein to the second submarginal cell. In certain of the subgenera (Protostelis, Microstelis and Pavostelis) the second recurrent vein terminates very close to the second transverse cubitus, or somewhat beyond it, while in Chelynia it has been thought that both recurrent veins terminated well within the limits of the second submarginal cell. This is true of S. (Stelidium) trypetina Robertson, and in S. foederalis Smith and S. nitida Cresson. However, in labiata Provancher, the genotype of Chelynia, this character is lacking in constancy, and in the type specimen, at the Provincial Museum of Quebec, the second recurrent vein is practically contiguous with the second transverse cubitus. It more nearly resembles Microstelis than it does the other species that have been placed in Chelynia. Moreover, in the males the telescoped abdominal sterna of labiata are nearly identical with those of Microstelis lateralis. It seems probable that Microstelis should be considered a synonym of Chelynia, while nitida and its allies should constitute a new subgeneric group. A revisional study of the New World species is needed, and the assignment of a name for the group is avoided here in the belief that it is better that a future reviser draw his own conclusions and propose an appropriate name if it is needed.
Species of Stelis are inquilines in the nests of Osmia, Hoplitis, Heriades, Anthidium and allies and possibly Ceratina.