Hawaii Yellow-masked Bee (Hylaeus simplex)
In the beginning of the 20th century the Hawaii Yellow-masked Bee was one of the most common members of its genus and could be found almost everywhere on its home island, from sea level up to the mountain rainforests.
Nevertheless the species is now considered extinct, whereby the reasons for its decline and, in the end, complete extinction are absolutely unknown.
 Howell V. Daly; Elwood Curtin Zimmerman; Karl N. Magnacca: ‘Insects of Hawaii; Volume 17; Hawaiian Hylaeus (Nesoprosopis) Bees (Hymenoptera, Apoidea). 2003
 K. N. Magnacca: Species Profile: Hylaeus simplex. In Shepherd, M. D. M. Vaughan, and S. H. Black (Eds.) Red List of Pollinator Insects of North America. The Xerces Society for Invertebrate Conservation, Portland, Oregon 2005