[2] In September 2016, along with six other Hawaiian Hylaeus species,[3] H. hilaris was listed for protection under the United States Endangered Species Act.

This marked a first listing for any bee species in the US.

Males have an almost completely yellow face with other yellow markings on the body and wings of smoky coloring.

[2] Hylaeus hilaris is now known only from a single population (of unknown size) in the coastal shrublands of the Moʻomomi Preserve on Molokai.

Threats to the species include habitat degradation by nonnative animals and plants, predation by nonnative insects, fires and climate change.