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

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

[2] Hylaeus assimulans is found in coastal and lowland dry forest.

Populations are now known only from the islands of Kahoolawe, Lanai and Maui.

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