Hylaeus facilis is a formerly widespread bee endemic to the islands of Oahu, Molokai, Lanai, and Maui in Hawaii. It is distinguished by its single, central face mark and unusually large gonoforceps. One of the most common species collected in the early 1900’s, it has been found very rarely in recent decades.
Males
Face marks yellow, consisting of a single large spot covering the entire clypeus and a narrow stripe in the paraocular area; otherwise unmarked. Process of the eighth sternum thin, not dilated; apices of gonoforceps very long, visible in situ. Hairs of abdominal apex brown, appressed.
Females
Entirely black, lacking coloration. Indistinguishable from females of H. difficilis and H. simplex. Hylaeus facilis is a member of the difficilis species group, possessing the characteristic facial marks and 8th sternum of that group. The large gonoforceps are unmistakable; its sister species, H. simplex, also has them enlarged, but they are not visible externally.
Taxonomic Status
Hylaeus facilis was described as Prosopis facilis by F. Smith (1879), and transferred to the new genus Nesoprosopis by Perkins (1899). Nesoprosopis was reduced to a subgenus of Hylaeus by Meade-Waldo (1923). The most recent taxonomic treatment was Daly and Magnacca (2003).
Hylaeus facilis has been collected from all habitats from the coast to wet forest, but probably prefers dry to mesic forest and shrubland. Nesting habits are unknown, but it probably nests in the ground like related species.
Historic collections of H. facilis are from Oahu, Molokai, Lanai, and Maui, and it was very widely distributed. Only three individuals have been collected in the last 50 years: one from Oahu (1975) and two from Maui (1967 and 1993).
Xerces Red List Status: Critically Imperiled
Other Rankings:
Canada – Species at Risk Act: N/A
Canada – provincial status: N/A
Mexico: N/A
USA – Endangered Species Act: Species of Concern
USA – state status: HI: Species of Concern
NatureServe: GNR
IUCN Red List: N/A
This species was found widely and abundantly, especially on Oahu, in the early period of Hawaiian insect collecting (1892-1930). It is now extremely rare and possibly in danger of extinction. Originally, U.S. Federal listings of rare and endangered species classed H. facilis as a “Category 2” Candidate Species about which more information was needed before it could be considered for listing. This status was based on recognition that Hawaiian bees in general were becoming rarer and little was known about their conservation status. Data were never gathered to document whether or not this species should be proposed for listing. It is currently considered to be a “Species of Concern” or a “Special Status Species” by the U.S. Fish and Wildlife Service and the Hawaii Division of Forestry and Wildlife.
The cause of the sharp decline in H. facilis is not clear, but it is probably due to habitat loss. Dry areas on Oahu and Maui Nui have been especially hard- hit by the combination of feral ungulates (especially goats) and subsequent invasion by exotic plants, as well as direct human modification. Although other related species (notably H. difficilis and H. laetus) are among the most common Hylaeus, they are abundant mainly on the islands of Kauai and Hawaii, where dry shrubland is relatively abundant; on the middle islands these species are rare as well.
The actual locations of remnant populations, if any, are not known. Although the 1993 collection gives hope that the species persists at least on Maui, it was taken in a residential area without native plants, and was probably a straggler from elsewhere. More intensive searching needs to be done to determine if cohesive populations exist in intact habitat, especially the small areas of dry forest on the leeward slope of Haleakala. Research is needed to search for extant populations, especially on Oahu and Maui.
Daly, H. V., and K. N. Magnacca. 2003. Insects of Hawaii, Vol. 17: Hawaiian Hylaeus (Nesoprosopis) Bees (Hymenoptera: Apoidea). University of Hawaii Press, Honolulu. 234 pp.
Meade-Waldo, G. 1923. Hymenoptera, fam. Apidae, subfam. Prosopidae, fasc. 181. Pp. 1-45 in P. Wytsman (ed.), Genera Insectorum. L. Desmet-Verteneuil, Brussels.
Perkins, R. C. L. 1899. Hymenoptera, Aculeata. Pp. 1-115 in D. Sharp (ed.), Fauna Hawaiiensis, Vol. 1. Cambridge University Press, Cambridge, United Kingdom.
Smith, F. 1879. Descriptions of new species of Aculeate Hymenoptera collected by the Rev. Thos. Blackburn in the Sandwich Islands. J. Linn. Soc. 14:674-685.
Profile prepared by Karl Magnacca, USGS-BRD, Kilauea Field Station
