Hylaeus leptocephalus

Taxonomy

Hylaeus leptocephalus, commonly known as the slender-headed masked bee, belongs to the genus Hylaeus in the family Colletidae. Hylaeus is the only truly globally distributed Colletid genus, occurring on all continents except Antarctica. 

Bees in the genus Hylaeus are different than many bees we find nesting in wood or stems; they belong to the family Colletidae, also known as “plasterer bees". Colletidae use a special secretion from their mouths, unique in their family, to line their nests. This family is considered a more ancient family of bees. Bees in the genus Hylaeus are sometimes called “yellow-faced bees” or “masked bees” because of the distinctive yellow markings on their faces.

Hylaeus leptocephalus is found in North America, primarily in the United States and Canada. This species usually inhabits environments with many flowering plants, including grasslands and prairies. 

Description

Hylaeus are very small, black, nearly hairless bees, frequently with yellow or white markings on their faces, collars and legs. Males have more yellow on the face, frequently filling the lower face between the eyes and looking more like a “mask.” Females frequently have yellow face markings restricted to two distinct triangles right near the eyes, sometimes described as “devil horns.” Hylaeus do not have pollen collecting hairs. Instead, they carry pollen and nectar home inside their bodies, in their crop. These are the smallest bees we find in stem or wood nests, and they can be easily mistaken for small Passaloecus wasps because they share similar size, body shape and color, and lack of hair. Passaloecus wasps can be distinguished by the wider, more square “block-head” look to their faces. They also often have silvery hairs on their faces, which Hylaeus bees do not have. Remember, Passaloecus wasps are shy and solitary like our bees, and they stock their nests with hundreds of aphids.

This bee species is characterized by its relatively small size and distinctively narrow head, which sets it apart from other members of the Hylaeus genus. Hylaeus leptocephalus are about 5 to 6mm long. In females, the body is mostly black, with lighter antennae underneath. Creamy white marks on the face fill the area between the mouth and eyes, stopping abruptly at the antennae. These marks also appear on the collar and front wings, transitioning to reddish-brown towards the back. The wings are lightly shaded with brown veins. The legs have yellow bases but are otherwise dark. The face tapers down, with cheeks about half as wide as the eyes. Small, shallow foveae are present on the face. Antennae segments vary in width, with the fourth segment nearly square.

In males, the body is black. The antennae are pale reddish-brown with black markings. The scape of the antennae is marked by a creamy, yellow spot. Their wings are lightly shaded with brownish veins. Cream-colored spots are found on the face, sides, and legs. H. leptocephalus males can be distinguished from other males due to their cream-colored facial markings, which are obliquely truncated above the antennae, with a slight divergence from the eyes above. The face is narrow, with converging eyes below and cheeks about half as wide as the eyes. The antennae are slender and curved, with the first segment wider than long, and the following segments about the same size.

Nest Structure

Unlike Megachilid bees, Hylaeus generally do not bring in outside materials to build their nests. Instead, they use a special secretion from their mouths, sometimes called “bee spit”, to line their nests and make their nest plugs. They have specially shaped tongues with broad ends that aid in “painting” the secretions inside the nests. The secretion dries to a thin, clear, water proof coating for the cells. Hylaeus nests have been known to be submerged in water and still emerge, and many species are associated with wetlands. Hylaeus provision their cells with a semi-liquid combination of nectar and pollen, instead of the more doughy “bee bread” of many solitary bee species. The cell lining is extremely delicate; a cellophane nest plug moves and crinkles easily with the lightest touch of a blade of grass. Plug appearance can vary from an opaque white color to an almost colorless, transparent film, like plastic wrap.

Hole Sizes

Hylaeus bees nest in column 3 holes (1/8-3/16") in Bee Atlas blocks.

Voltinism

We are looking into whether these bees have more than one generation per year and are interested to hear from anyone who has them in their blocks.

Activity Period

No information at this time.

References

Discover Life. Hylaeus male guide. Available at: https://www.discoverlife.org/mp/20q?search=Hylaeus+leptocephalus&guide=Hylaeus_male. (Accessed May 10, 2024).