I first learned about these little-known tiny pollinators of the Hylaeus genus, called masked or faced bees, when researching my 2016 Useful Calendar, which featured watercolor illustrations and info about 12 wild bees from around the world.
I then made a small zine with those illustrations and more information about each type of bee, and about wild bees in general (because there's only so much room for that sort of thing on a calendar). The zine, called The Flower Lovers, is available from my Etsy shop or, in Minneapolis, from Moon Palace Books (on Minnehaha Avenue and E. 33rd St., next to Peace Coffee).
I also made a page on this blog, About the Bees, with info and links about the 12 bees.
Here's an excerpt from my bee zine, the part about Hylaea, updated to reflect this new development:
Masked bee / Hylaeus spp.
Description: Also called yellow-masked or yellow-faced bees, Hylaea are distinguished by the bright white or yellow patch on their faces. Just 5 to 7 mm long, their slender black bodies may resemble wasps, but are not as shiny. They have tiny plume-like hairs on their abdomen and thorax.
Where found: About 700 species are known worldwide, most notably on islands; they are abundant in Australia, and the only bee native to Hawaii. Fifty species exist in North America, from the Arctic circle to the tip of Florida. Sixty species are endemic to Hawaii and found nowhere else; of these, some are thought to be extinct, having not been seen in 80 years.
Nest: They are solitary bees that mostly nest in hollow stems and twigs; some nest in the ground if they find an abandoned burrow made by another insect (they do not have strong mandibles for digging their own burrows). They have also been known to nest in nail holes and manmade nesting structures using paper straws.
Habitat: The name Hylaeus means “of the woods,” referring to this genus’s preference for nesting in woody materials, and for their relative abundance in forests, where other bees are not common. They are found in diverse natural habitats where trees and shrubs grow, in coastal regions and mountainsides. In Hawaii, they are absent from developed areas dominated by non-native plants.
Food sources: They visit a variety of wildflowers — many endangered native plants of Hawaii depend on these bees for pollination — and they do not care for most introduced crops or flowers. They take pollen and nectar into their crop and then regurgitate it in cellophane-like sacs to feed their larvae.
Notes: Hylaea are found on islands much more than other types of bees; this may be due to their predilection for nesting in wood—possibly migrating unintentionally via driftwood.
The Xerces Society has successfully petitioned to protect seven of the Hylaeus species in Hawaii under the U.S. Endangered Species Act, because they are threatened by development and other threats to their habitat, non-native animals, including ants and feral pigs, and the decline of native wildflowers. These are the first bees to be so listed.