Yellow faced bees: Hylaeus ombrias
(Hymenoptera: [Apoidea:] Colletidae: Hylaeinae)
Profile prepared by Karl Magnacca, USGS-BRD, Kilauea Field Station
Hylaeus ombrias is a coastal and dry forest bee endemic to the island of Hawaii in Hawaii. It is distinguished by its large size compared to other coastal species, and reduced facial marks. It is typically found as scattered individuals, and habitat destruction has caused its range to contract significantly.
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 not widely collected by Perkins, possibly because coastal habitat in Kona was already degraded by that time. The habitat available to H. ombrias has certainly constricted in historic times as invasive plants have moved in and the diversity of dry forest has been reduced. Although H. ombrias is not associated with Chamaesyce like other sympatric dry forest species, it does require some diversity in available plants, such as Bidens and Sida. Originally, U.S. Federal listings of rare and endangered species classed H. ombrias 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.
Males: Face with yellow lateral marks narrowing dorsally; clypeal mark not filling the entire plate, sometimes absent. Scape widest near the middle. Process of the eighth sternum narrowly dilated. Hairs of abdominal apex brown, appressed.
Females: Entirely black, lacking coloration. Large, but without distinct punctation on the abdomen.
Hylaeus ombrias is sister to H. assimulans in the flavipes species group; males can be told apart by the reduced facial markings of H. ombrias, but females cannot be reliably distinguished except by distribution. The two species are considerably larger (especially in the females) than any other Hawaiian species except those in the pubescens group, which have the abdomen punctate.
Hylaeus ombrias was described as Nesoprosopis ombrias 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 ombrias inhabits coastal strand and dry forest. It is frequently collected on Sida fallax (ilima); its greater size may be an adaptation to handling the large pollen of that plant. In recent collections, it appears to be less restricted to the coast and more often found in higher elevation forest than other species of similar habit. Such a tendency may be related to the dense areas of Sida that can be sometimes be found in the understory of dry forest. Unlike other species collected in the Puu Waawaa/Pohakuloa dry forest area, it does not appear to be strongly associated with Chamaesyce olowaluana. Nesting habits are unknown, but it probably nests in the ground like related species.
Historic collections of H. ombrias are from South Kona. Recent collections have come from two widely disjunct populations: one coastal population at South Point, and a montane one in the dry forest area between Mauna Kea, Mauna Loa and Hualalai.
The greatest threat to H. ombrias is habitat loss. Dry forest has been heavily impacted by feral ungulates and invasive plants, and much coastal strand has been destroyed by development.
All known montane populations of H. ombrias are protected under the auspices of the State of Hawaii or the U.S. Army, though they may not be actively managed for habitat conservation. These sites are highly susceptible to fire. The coastal population is not protected and may be affected by the large number of visitors to the area.
Maintenance of remaining habitat is the highest priority. Research is needed in order to determine life history requirements, including nest sites and pollen requirements.
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.
Bishop Museum Arthropod Species of Concern checklist. Lists H. ombrias as a Species of Concern. Updated February 21, 2000.
Magnacca, K. N. 2005. Species Profile: Hylaeus ombrias. In Shepherd, M. D., D. M. Vaughan, and S. H. Black (Eds). Red List of Pollinator Insects of North America. CD-ROM Version 1 (May 2005). Portland, OR: The Xerces Society for Invertebrate Conservation