Yellow-Faced Bee - Hylaeus
By Evan Cole, Pollinator Partnership
The genus Hylaeus, commonly known as yellow-faced bees, consists of more than 500 species within the family, Colletidae. There are currently about 130 species of hylaeus in America. Typically 5-7mm long, yellow-faced bees resemble tiny black wasps, with yellow-white markings on their face, legs, and thorax. However, wasps possess short hairs that glisten in the sunlight, while yellow-faced bees are virtually hairless. Despite having relatively small tongues, yellow-faced bees are very slender and can easily squeeze deep into flowers to collect pollen and nectar.
The most unique feature of yellow-faced bees is that, unlike most other bees, they do not possess scopa. Scopa are external appendages used to carry pollen, such as dense masses of setae, or hair, on the hind legs. Instead, yellow-faced bees carry pollen in a special compartment of their stomach, known as the crop. They transport the pollen in the crop, sometimes referred to as the honey stomach, and then regurgitate it at the nest.
Yellow-faced bees are solitary bees, typically nesting in existing tunnels or holes in wood or stems. They create brood cells with a cellophane-like material, which they also use to line their nest with. Upon returning to the nest after foraging, the female regurgitates the contents of her crop into individual brood cells. An egg is laid in each cell, and the larvae can then eat the liquid mixture of pollen and nectar when they hatch.
Appearing between May and September, yellow-faced bees are most prominent in early spring and late summer. In spring, they are frequently found foraging on Golden Alexanders (Zizia spp.), and are important pollinators for this genus of plants in the carrot family. In late summer, yellow-faced bees enjoy feeding on the pollen and nectar of Swamp Milkweed (Asclepias incarnata) and Common Boneset (Eupatorium perfoliatum), among other native plants.
There are a number of unique and fascinating species of yellow-faced bees in North America, many of which are endemic to Hawaii, meaning that they are only found there. Hylaeus akoko is an extremely rare species of yellow-faced bee found only on the island of Hawaii. This endemic species is listed as critically imperiled on the Xerces Society Red list because of its extremely narrow range and sparse numbers. Another species endemic to Hawaii, Hylaeus anomalus, is only found on the island of Oahu. The female of this species has a distinctive red head, and the base of the male’s abdomen is bright orange. On the North American mainland, there is Hylaeus lunicraterius, a rare species of yellow-faced bee found only at the Craters of the Moon National Monument in Idaho. The area is a harsh volcanic landscape, but Hylaeus lunicraterius is able to nest in the crevices of hardened lava. The Monument is a protected site, but this species is still immensely fragile due to its small and isolated range.