ID GUIDE TO WILD BEES
OF THE NATIONAL BUTTERFLY CENTER

Mission, Texas

YELLOW-FACED  BEES
Hylaeus

Yellow-faced bees, sometimes called "masked 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. 

 

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 such as Rockefeller Park.

 

Yellow-faced bees have short tongues, but according to the Xerces Society's Guide to Attracting Native Pollinators, 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 and roses.  Nonetheless, in the park and Stone Barns, these bees show a strong preference for small-blossomed plants such as Queen Anne's lace, goldenrod and yarrow. 

Identification Information:   There are 18 species of masked bees in New York State. Most are between 1/8" and 1/4" in size -- a few  run as large as 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.

 

The yellow-faced bee shown at top right, known as a modest masked bee (Hylaeus modestus modestus), is barely 1/5" long -- and yet, this is the largest of the three species shown here. Modest masked bees appear in the park and Stone Barns in May, disappear in mid-summer and reappear in late August and September.  These bees are generalist pollinators, but in the park and Stone Barns, they are found most frequently feeding on goldenrod, Queen Anne's lace and carrot flowers.

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 yellow lining 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 be shown below.

 

Modest masked bee females have two irregular yellow triangles on their faces, as shown in the photo strip at right.  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 constricted face markings than the female Hylaeus modestus modestus.

Cresson's masked bee (Hylaeus mesillae cressonii) is an eastern subspecies of the Mesilla masked bee (Hylaeus mesillae).  To the naked eye, Hylaeus mesillae closely resembles the modest masked bee discussed above --  but is much smaller and lacks a yellow collar on the pronotum (the front end) of the thorax.  The female bee shown here was barely 1/6" long. Males tend to be smaller, and may be as tiny as 1/8".

 

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.  (This species has not yet been documented in the preserve or Stone Barns). Mesilla masked bees feed on an extensive range of plants, although in our area, they commonly feed on goldenrod and Queen Anne's lace.

The slender-faced masked bee (Hylaeus leptocephalus) has been found only once at Stone Barns, during late summer in a field containing legumes such as clover and bird's-foot trefoil.  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.

 

This tiny bee 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.  The male bee shown at right is minuscule -- barely 1/6" in length. Females are somewhat larger, at times topping 1/5".

 

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.

THESE TWO PICTURES ARE FROM NEW YORK 

Hylaeus modestus modestus):
Note the yellow collar on the front of the bee's thorax.

THE PHOTOGRPAHS ABOVE AND BELOW ARE FROM NEW YORK:  Comparison of facial markings of three masked bees:  a female modest masked bee (left); a male slender-faced bee (center) ; and a a female Cresson's masked bee (right).

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
                 s
lender-faced masked bee

JACK NEFF AGREED THIS WAS A MODEST MASKED BEE, BUT COULD IT BE SOMETHING ELSE?  JEFF THOUGHT THE FACE WAS NOT QUITE RIGHT.

Modest masked bee
Nomia tetrazonata uvaldensis

 

Family:  Halictidae

Size:  5.5 mm

Associated plants at NBC:  

Low croton
(Croton humilis)

Plant family:    Euphorbiaceae

When seen:   April 2019   

Male bee

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Male bee

Hylaeus Species of the National Butterfly Center

Permissions and Copyright Information:   All images on this site are (c) Copyright 2018-2019 Paula Sharp and Ross Eatman.  All rights reserved. All photographs are protected by registered copyright.  Please contact Sharp-Eatman Nature Photography for written permission before using any of these images for any purpose. 

Last updated November 2019

 1-15-19