Hylaeus mesillae

Taxonomy

Hylaeus mesillae, commonly known as the Mesilla masked bee, belongs to the genus Hylaeus within 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.

This species can be found across North America, from the southern parts of Canada down to the northern areas of Mexico (hence the name “Mesilla”). 

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.

Hylaeus mesillae are some of the smaller species of Hylaeus that we encountered at the MN Bee Atlas. They range in size from 3.5 to 4mm. Females are black with yellow markings on their face and body. Like many other females of different species, H. mesillae has facial markings that are yellow, triangular, and end sharply at the edge of the eye, just a bit above where the antennae are. This can potentially make it hard to distinguish from females of other species. Its antennae are dark brown on top and light brown underneath. The wings are mostly clear with brown veins and a brownish spot. The collar is black. The mid-legs of H. mesillae are usually yellow, while the rest are dark. Its face is slim, with deep foveae that are relatively close to the margin of the eyes.

Males of this species look similar to the females. Their bodies are mostly black with the underside of their antennae being a lighter brown. The collar and tegulae are black. Wings have brownish veins and stigma. Mandibles and labrum are black. There are yellow markings on various parts of the males’ bodies including on the front of the scape, tubercles, parts of the legs, and tarsi/spurs. The facial markings of male H. mesillae specimens are distinct from other species found in the MN Bee Atlas Bee blocks as the yellow marks on the face extend upward over the antennae, forming narrow rounded lobes that are separate from the edge of the eye and partly encircle the area where the antennae connect. The face is narrow and long, with cheeks narrower than the eyes. The first antennae segment is short and wide.

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 mesillae." Discover Life, accessed May 24, 2010, https://www.discoverlife.org/mp/20q?search=Hylaeus+mesillae&guide=Hylaeus_male.