The Great Sunflower Project

Hylaeus- yellow-faced bees/masked bees (family Colletidae)

Genus summary: Hylaeus has worldwide distribution. There are approximately fifty species in North America (Michener 2000), about 20 in the northwestern portions of Canada and the U.S. (Stephen et al. 1969), and 16 are known from New York State (Danforth & Magnacca 2002). The diversity in Hawaii is incredible with 60 species (Magnacca 2007). However, in most locations, Hylaeus species make up only a small percentage of the total bee fauna (Michener 2000).

Floral relationships: Hylaeus do not carry pollen or nectar externally; they instead store their food in the crop and regurgitate it upon returning to their nests. Thus, it is difficult to assess what flowers they visit, although it is suspected that they are primarily generalist foragers [michener 2000]. Hylaeus are short-tongued, but their small body size may enable them to access deep flowers.

Nesting habits: Hylaeus are solitary tunnel nesters (O’Toole & Raw 1999). Hylaeus lack strong madibles and other structural adaptations for digging; thus, many species rely on nest burrows made by other species (Magnacca 2007). Most species nest in stems and twigs [gretchen]. They line their nest cells with a self-secreted cellophane-like material {michener 2000}. A few species are specialist nesters.

Diagnostic characteristics: Hylaeus are minute to small bees between 0.2 to 0.3 inches long (Michener 2000). They are usually hairless, slender and superficially resemble small wasps. They are usually black with bright yellow or white markings on their face and thorax. Hylaeus lack pollen-carrying scopa and instead carry their provisions in their crop.

Similar taxa: Hylaeus may easily be mistaken for small sphecoid wasps, but there are a couple of distinguishing characters. Sphecoid wasps have silvery or gold hairs on the lower part of their face that make it look like their face is glittering in the light, whereas Hylaeus do not. In addition, if you use a microscope, Hylaeus, like all bees, have branched (plumose=feathery) hairs while wasps have unbranched hairs (Michener 2000).

Known conservation concerns: Twenty-seven Hylaeus spp. are on the Xerces Society Red List of Pollinator Insects. Eighteen are listed as Critically Imperiled, seven as Critically Imperiled and Possibly Extinct, one as Imperiled and one is listed as Vulnerable (Shepherd 2005). One species, H. lunicraterius, lives only at Craters of the Moon National Monument in Idaho. This habitat is protected, but any species with such limited distribution is at risk. The other 27 threatened species are endemic to Hawai’i! Hylaeus are the only genus of bees native to Hawai’i. Five species have not been collected recently from one or more sites where they were found historically, seven are restricted to endangered habitat, ten are rare, and ten could be extinct (Magnacca 2007).

Interesting Fact: Many Hylaeus species in Hawai’i may be threeatened by invasive ants. Where two of these species, the long-legged ant (Anoplolepis longiceps) and the big-headed ant (Pheidole megacephala) were abundant on Maui, there were no Hylaeus nests (Daly & Magnacca 2003).

Additional resources: Magnacca (2007), Daly & Magnacca (2003)

Key to Hylaeus at Discover Life