SHARP-EATMAN
NATURE
PHOTOGRAPHY
MASKED BEES, sometimes called "yellow-faced bees," comprise the genus Hylaeus and belong to the bee family Colletidae. Yellow-faced bees are easy to overlook -- they're small and slender. They are often mistaken for tiny wasps, because yellow-faced bees are hairless and black with yellow markings.
Typically, yellow-faced bees found in our area have yellow designs or "masks" on their faces; parti-colored yellow-and-black legs; and yellow markings on their thoraxes. The bees' abdomens are usually entirely black, without yellow markings, a trait that helps distinguish them from wasps, as noted below.
BUGUIDE NOTES: "
Unique yellow patterning on face beside the eyes (females) or extending across much of the lower face (males).
No metallic sheen.
No pollen-collecting hairs.
Two submarginal cells, with the second shorter than the first.
Face usually elongate, with eyes strongly converging below."
Yellow-faced bees are unusual -- the females carry pollen internally, in stomach-like organs, instead of transporting it on their legs or abdomens like most bees.
Female masked bees build nests in the stems of pithy-stemmed plants such as sumac and elderberry. The bees secrete a substance said to have a texture similar to polyester, with which they coat the brood cells in which they deposit their eggs. Because of their preference for woody nesting materials, bees of the genus Hylaeus (Latin for "of the woods") often abound in woodland habitats.
Yellow-faced bees have short tongues, but the bees' small size allows them to enter into deep-throated flowers to harvest pollen and nectar, unlike large short-tongued bees. Most yellow-faced bees of our area are generalist pollinators, foraging on a wide gamut of plants, among them milkweed, dogbane, asters, Canada thistles, blackberries, roses, and goldenrod.
Identification Information: There are 18 species of masked bees in New York State. Most are between 3.5 to 7 mm (1/8" and 1/4") in length -- a few run as large as 8.5 mm (1/3") Differentiation among species is difficult to undertake with the naked eye, because the bees are so small and nuances in their appearance minute. One trait that helps to distinguish them is the nature and size of the yellow or white "masks" or markings on the bees' faces, which vary from one species to another.
Facial markings also differ in male and female masked bees: markings of males tend to cover a large area of the face, while on females, the markings are smaller and often restricted to two bands or to two roughly triangular shapes on either side of the bee's face. In most species, males are also smaller than their female counterparts.
Modest masked bee
(Hylaeus modestus modestus)
Size: 4-7 mm (female)
4.5 - 7 mm (male)
Although modest in size (1/8-1/4 in., or 4-7 mm), this is the largest of the three Hylaeus species shown here. Modest masked bees appear in southern New York in May, dwindle in numbers in early July, and resurge in late August and September. These bees are generalist pollinators, but they are found most frequently feeding on small-flowered plants such as goldenrod, Queen Anne's lace and carrot flowers. They appear in both natural settings and gardens and are
Modest masked bees have yellow markings on all six legs (on the base of each tibia), and yellow markings on the sides of their thoraxes (on the tubercles). They usually have a collar of yellowthat lines the front of the thorax (the pronotum); this trait aids in distinguishing them from some other yellow-faced bee species, such as Cresson's masked bee.
The female modest masked bee females has a black clypeus (the face part above the mandibles). As shown in the accompanying photo strip, a pair of irregular, roughly triangular, yellow markings extend along the inner edges of the female's compound eyes. On males, the yellow markings cover a larger area.
Hylaeus modestus modestus is an eastern subspecies of Hylaeus modestus. The bee's western counterpart, the subspecies H. modestus citrinifrons, has black front tibia, and females of that subspecies have more limited facial markings than the female Hylaeus modestus modestus.
A female modest masked bee (Hylaeus modestus modestus)
Comparison of facial markings of three masked bees: a female modest masked bee, a male slender-faced masked bee bee; and a female Cresson's masked bee
A female modest masked bee (Hylaeus modestus modestus). This bee is 1/4" long.
Female modest masked bees of the subspecies Hylaeus modestus modestus have two roughly triangular patches of yellow on their faces.
The clypeus (the face part just above the mandibles) of the female modest masked bee is black.
Both male and female modest masked bees usually have a collar of yellow at the front of the thorax. This is a female bee.
Modest masked bees have partly yellow legs. Their abdomens are entirely black.
Male (top) and female (below) modest masked bees foraging on carrot flowers: males typically are smaller than females.
Close-up of a male modest masked bee: the facial markings on males are more extensive than on females.
A female Cresson's masked bee, a subspecies of the mesilla masked bee. This bee is barely 1/6" long.
Cresson's masked bee
(Hylaeus mesillae cressonii)
Size: 4-4.5 mm (female)
3.5-4 mm (male)
Cresson's masked bee is an eastern subspecies of the Mesilla masked bee (Hylaeus mesillae). To the naked eye, Hylaeus mesillae resembles the modest masked bee discussed above -- but M. melisillae is much smaller, and it lacks a yellow collar on the pronotum. Both males and females have yellow markings on the face and legs and pronotal lobes.
Mesilla masked bees feed on an extensive range of plants, although in our area, they are commonly found on goldenrod and Queen Anne's lace. The bee shown here was found foraging on goldenrod in mid-September, in a sandy area bordering a railroad access nine miles north of Rockefeller State Park Preserve of Westchester County.
Slender-faced masked bee
(Hylaeus leptocephalus)
Size: 5-6 mm mm (female)
4.-6 mm (male)
This species is originally from Europe and not native to our area. According to a 1970 article by entomologist Roy R. Snelling, the slender-faced masked bee appeared in North Dakota as early as 1912 and has since established itself in states throughout the country.
Slender-faced masked have been documented rarely in Westchester County, New York, and are relatively uncommon in New York generally The bee shown here was discovered at Stone Barns Center for Food and Agriculture dDuring late August of 2017, feeding on bird's-foot trefoil.
Hylaeus leptocephalus is a pollinator of elderberries and a range of other native flowering plants such as dogbane, heath aster, goldenrod and Queen Anne's lace. The slender-faced masked bee, however, is unusual among yellow-face bees, because it shows a tendency toward specialization. Slender-faced masked bees manifest a strong preference for plants of the legume family, especially Melitotus (sweet clover).
The slender-faced masked bee has a narrow face shaped like an elongated trapezoid. This bee has ivory rather than yellow markings, which appear on the bee's face, legs and thorax.
Masked bees vs. wasps: As noted, because they are slender and hairless, lack pollen-carrying structures and have black-and-yellow markings, yellow-faced bees are easily confused with wasps. In particular, they superficially resemble two small wasps in our area -- the bee wolf (Philanthus) and the beetle wasp (Cerceris), which often frequent the same plants as yellow-faced bees at Rockefeller Park and Stone Barns. These wasps are shown in the photo strip at right. They can be distinguished readily from yellow-faced bees, because the wasps have yellow stripes circling their abdomens.
TAXONOMY - Modest Masked Bee
Order: Hymenoptera
Family: Colletidae (plasterer and masked bees)
Genus: Hylaeus (masked bees)
Subgenus: Prosopis
Species: Hylaeus modestus
Subspecies: Hylaeus modestus modestus (modest masked bee sensu stricto)
TAXONOMY - Cresson's Masked Bee
Order: Hymenoptera
Family: Colletidae (plasterer and masked bees)
Genus: Hylaeus (masked bees)
Subgenus: Hylaeus (Nominate masked bees)
Species: Hylaeus mesillae (Mesila masked bee)
Subspecies: Hylaeus mesillae cressonii
(Cresson's masked bee)
TAXONOMY - Slender-faced Masked Bee
Order: Hymenoptera
Family: Colletidae (plasterer and masked bees)
Genus: Hylaeus (masked Bees)
Subgenus: Hylaeus (Nominate masked bees)
Species: Hylaeus leptocephalus
slender-faced masked bee
Masked Bee Species
Modest masked bee
(Hylaeus modestus modestus)
Size: 4-7 mm (female)
4.5 - 7 mm (male)
Although modest in size (1/8-1/4 in., or 4-7 mm), this is the largest of the three Hylaeus species shown here. Modest masked bees appear in southern New York in May, dwindle in numbers in early July, and resurge in late August and September. These bees are generalist pollinators, but they are found most frequently feeding on small-flowered plants such as goldenrod, Queen Anne's lace and carrot flowers. They appear in both natural settings and gardens and are
Modest masked bees have yellow markings on all six legs (on the base of each tibia), and yellow markings on the sides of their thoraxes (on the tubercles). They usually have a collar of yellowthat lines the front of the thorax (the pronotum); this trait aids in distinguishing them from some other yellow-faced bee species, such as Cresson's masked bee.
The female modest masked bee females has a black clypeus (the face part above the mandibles). As shown in the accompanying photo strip, a pair of irregular, roughly triangular, yellow markings extend along the inner edges of the female's compound eyes. On males, the yellow markings cover a larger area.
Hylaeus modestus modestus is an eastern subspecies of Hylaeus modestus. The bee's western counterpart, the subspecies H. modestus citrinifrons, has black front tibia, and females of that subspecies have more limited facial markings than the female Hylaeus modestus modestus.
Identification information: Bees of the n appearance.
A female modest masked bee (Hylaeus modestus)
Affiliated masked bee
(Hylaeus affinis)
Size: 4-7 mm (female)
4.5 - 7 mm (male)
Although modest in size (1/8-1/4 in., or 4-7 mm), this is the largest of the three Hylaeus species shown here. Modest masked bees appear in southern New York in May, dwindle in numbers in early July, and resurge in late August and September. These bees are generalist pollinators, but they are found most frequently feeding on small-flowered plants such as goldenrod, Queen Anne's lace and carrot flowers. They appear in both natural settings and gardens and are
Modest masked bees have yellow markings on all six legs (on the base of each tibia), and yellow markings on the sides of their thoraxes (on the tubercles). They usually have a collar of yellowthat lines the front of the thorax (the pronotum); this trait aids in distinguishing them from some other yellow-faced bee species, such as Cresson's masked bee.
The female modest masked bee females has a black clypeus (the face part above the mandibles). As shown in the accompanying photo strip, a pair of irregular, roughly triangular, yellow markings extend along the inner edges of the female's compound eyes. On males, the yellow markings cover a larger area.
Hylaeus modestus modestus is an eastern subspecies of Hylaeus modestus. The bee's western counterpart, the subspecies H. modestus citrinifrons, has black front tibia, and females of that subspecies have more limited facial markings than the female Hylaeus modestus modestus.
Identification information: Bees of the subgenus Stelis (Dolichostelis) have a slender shape, and are black with pale or yellow markings and coarse punctures on their bodies. On both male and female Dolichostelis, the area between the antennae is short and somewhat protuberant.
Bees of the subgenus Dolichostelis can be identified by this trait (shown in the accompanying photo strip): the base of the propodeum is set off from the metanotum by a ridge and zone divided into a series of long pits. (The metanotum is the rearmost thorax segment, and the propodeum is directly behind it.)
Stelis louisae specifically have yellow face markings edging their compound eyes; yellow lines tracing the rims of their thoraxes; and yellow stripes banding their abdomens. The legs of Stelis louisae are reddish and their wings transparent brown. The reddish coloration of the bees' legs tends to be more pronounced in the bees' southern range. Males and females are very similar in appearance.
Stelis louisae can be distinguished from other Dolichostelis by the broken yellow line on the second abdominal segment (T2) as shown in the photo strip here. The yellow markings on Stelis louisae also tend to have an orangish tinge. Both females and males have broad yellow stripes along the inner rims of their compound eyes. On males, a thick yellow mark n the lower face connects the two stripes.
A female affinilated masked bee (Hylaeus affinis)
RECOMMENDED REFERENCES - Stelis
Ascher, John S., & John Pickering. Species Descriptions and Keys for Stelis. Discover Life Bee Species Guide and World Checklist (Hymenoptera: Apidae: Anthophila). Discover Life. https://www.discoverlife.org/20/q?search=Apoidea#Identification
Danforth, Bryan N., Robert L. Minckley, & John L. Neff. The Solitary Bees: Biology, Evolution, Conservation. Princeton: Princeton University Press, 2019.
Michener, Charles D. 2007. The Bees of the World (2nd ed.). Johns Hopkins University Press, Baltimore and London, 953 pp.
Michener, Charles D. 1955. Some biological observations on Hoplitis pilosifrons and Stelis lateralis (Hymenoptera, Megachilidae). Journal of the Kansas Entomological Society 283:81-87.
Mitchell, Theodore B. 1962. Bees of the Eastern United States. Vol. 2. North Carolina Agricultural Experimental Station Technical Bulletin No. 152.
Metz C.W. 1911. A revision of the genus Prosopis in North America. Transactions of the American Entomological Society 37(2): 85-156.(Text)
Say, T. 1837. Descriptions of new North American Hymenoptera, and observations on some already described. Boston Journal of Natural History, 1(4), 361–416. (Contains the original description of Hylaeus modestus under Prosopis).
Smith, F. 1853. Catalogue of Hymenopterous Insects in the Collection of the British Museum. Part I. Andrenidae and Apidae. London: British Museum. (Contains the original description of Hylaeus affinis).
Snelling R.R. 1966 Studies on North American Bees of the genus Hylaeus. 1. Distribution of the western Species of the Subgenus Prosopis with descriptions of new forms (Hymenoptera: Colletidae). Contributions in Science, Natural History Museum of Los Angeles County 98: 1-18.
Snelling R.R. 1966. Studies on North American bees of the genus Hylaeus. 3. The Nearctic subgenera (Hymenoptera: Colletidae). Bulletin of the Southern California Academy of Sciences 65(3): 165-175.
Snelling R.R. (1970) Studies on North American bees of the genus Hylaeus. 5. The subgenus Hylaeus, s. str. and Paraprosopis (Hymenoptera: Colletidae). Contributions in Science, Natural History Museum of Los Angeles County (180): 1-59.
Snelling R.R. (1983) Studies on North American Bees of the genus Hylaeus. 6. An adventive Palearctic species in Southern California (Hymenoptera: Colletidae). Bulletin of the Southern California Academy of Sciences 82: 12-16.