What role do the metallic sheens found on some *Hylaeus* species play in identification?

Metallic sheens, presenting as bronze, blue, or green, can subtly differentiate species under direct light.

While the primary characteristic of the genus is the yellow face set against a typically black or dark brown body, some species possess additional visual complexity in their coloration. Depending on the specific species, the thorax or abdomen may exhibit a metallic sheen. When observed under direct illumination, this sheen can manifest in subtle shades such as bronze, blue, or green. Although the core identification relies on the facial markings and smooth body, the presence and specific hue of these metallic qualities serve as secondary, distinguishing features that help researchers separate one species from its closely related counterparts.