SHARP-EATMAN
NATURE
PHOTOGRAPHY
SWEAT BEES. Halictidae, tiny nonaggressive "sweat bees," comprise one of the seven bee families in the insect order Hymenoptera. These bees are a highly important group of wild pollinators, responsible for the pollination of an impressive range of commercial crops -- among them squash, legumes, sunflowers, watermelons, apples, cranberries, blueberries, strawberries, tomatoes and peppers, to name but a few. Sweat bees are also essential pollinators of native flora, appearing in all seasons in New York on an extensive array of flowering plants found in woodlands and fields.
Sweat bees come in a multitude of varieties and colors, and span 14 genera within the United States and a seemingly endless plenitude of species. (The single sweat bee genus, Lasioglossum, for example, is represented by 160 different species in New York.) Sweat bees shown in this guide represent six genera that can be grouped roughly by their salient characteristics: (1) iridescent green bees (Agapostemon, Augochlora, Augochloropsis and Augochlorella), covered in this guide's preceding section; and (2) dark sweat bees, presented hereI. Dark sweat bees may be black, brown or darkly-metallic, often with striped abdomens and sometimes with red abdomens. In our area, dark sweat bees divide mainly into two genera -- Halictus and Lasioglossum. Below is a sampling of Halictus and Lasioglossum sweat bees inhabiting Rockefeller State Park Preserve and Stone Barns Center for Food and Agriculture.
Lasioglossum Sweat Bees
Lasioglossum are slender, small sweat bees, ranging between 1/2" and 1/10" in length. They are often darkly colored, with or without pale bands of hair on their abdomens; some are metallic. Males sometimes have partly yellow faces or legs.
Female Lasioglossum carry pollen conspicuously, on scopal hairs located on the upper sections of their hind legs, like the bee shown at right. This bee, found nectaring on a wild rose at Stone Barns in late spring, is a typical dark Lasioglossum: it is slender, dark-bodied and barely 1/4" long, with narrow off-white bands on its abdomen. The bee below it is a typical metallic Lasioglossum -- a 1/4" dark bronze bee with short, pale hairs on its head, legs and body.
Lasioglossum of ou area tend to be generalist pollinators, although some species specialize on particular plants. Lasioglossum appear in the park and Stone Barns wherever flowers abound. Despite their size, Lasioglossums are considered chief pollinators of wildflowers, garden flowers and vegetable crops.
Sweat bees of the genus Lasioglossum tend to build nests in loose soils, consisting of single narrow shafts with series of branches. The bees secrete a waxlike substance used to line their brood cells. The habits of this broadly-defined genus vary widely by species: some Lasioglossum are solitary, but others form semi-social groups or colonies.
A dark Lasioglossum sweat bee with a striped abdomen (female)
Lasioglossum vs. Halictus striped sweat bees:
According to entomologist Charles D. Michener, author of the voluminous The Bees of the World, two traits aid in distinguishing striped Lasioglossum sweat bees from striped Halictus sweat bees (shown higher up on this guide page). These traits relate to wing venation and the positioning of hair bands on the bees' abdomens.
As shown in the photo strip here, the veins on the outer edges of Lasioglossum wings may be indistinct. By contrast, the wing veins of Halictus (such as those found in our area) tend to be boldly defined throughout.
In addition, on striped Lasioglossum sweat bees, pale hair bands appear on the inner edge of each abdomen segment (the edge closer to the bee's head). Conversely, on Halictus like the ligated sweat bee shown above, the pale hair bands are on the outer edge or rim of each segment (the edge closer to the abdomen's tip). This is also shown in the photo strip.
TAXONOMY: The sweat bee genus Lasioglossum is represented by 280 species in North America, and 170 in New York alone. Hairsplitting differences among Lasiglossum species make identification of individual types challenging. Charles D. Michener dedicated twelve pages of fine print to the taxonomical traits of various Lassioglossum in The Bees of the World, after describing them as "a genus of morphologically monotonously similar bees”.
There are five subgenera of Lassioglossum in the United States and Canada. Four have been found in the park and Stone Barns: Dialictus; Lasioglossum; Sphecodogastra; and Evylaeus. A sampling of these is shown below.
Taxonomy of Lasioglossum Sweat Bees
Order: Hymenoptera
Family: Halictidae (Sweat Bees)
Subfamily: Halictinae
Tribe: Halictini
Genus: Lasioglossum
Subgenera shown here:
Lasioglossum
Sphecodogastra
Evylaeus
Dialictus
A metallic Lasioglossum sweat bee (female)
A female striped Lasioglossum sweat bee foraging on a wild rose.
Note that the veins of the bee's wings weaken as they approach the wing tip.
Close-up of the wing of a Lasioglossum sweat bee
Halictus: Furrow Bees
Ligated Furrow Bee
Halictus Ligatus
(Subgenus Odontalictus)
1/5 - 1/3" (very small)
Halictus sweat bees, also known as furrow bees,
are found throughout throughout the world. There are 25 species in the Americas, and 6 in the New York area. Halictus native to New York are small to very small, dark brown or dark-metallic bees with pale bands of hair on their abdomens. Females carry pollen on scopae (sticky brushes) located on their darkly-colored hind legs. Males lack scopal hairs and tend to have partially yellow legs.
Halictus of our area are generalist foragers that pollinate a broad range of wildflowers and garden flowers as well as commercial crops. The bees nest in the ground, in loose soils. Some Halictus are solitary and others nest in semi-social groups that pass through multiple generations in a single summer. Halictus are a common sight in the park and at Stone Barns Center for Food and Agriculture. They first appear in early spring and remain through mid-fall.
Halictus ligatus. A ligated furrow bee is smaller than the head of a dime. If you look carefully at the coneflowers in the park's Visitor Center garden, you might well see two or three of these wild bees on a single blossom. Halictus ligatus are often found on aster- family flowers such as coneflowers, sunflowers and daisies. Despite their small size, ligated furrow bees are considered important pollinators of commercial sunflower crops -- they are avid pollinators of sunflowers at Stone Barns' vegetable fields.
Ligated furrow bees are also key generalist pollinators of wildflowers. These wild bees, however, have short tongues and are unable to forage for nectar in deep-throated blossoms. The bees are so small that when they feed on milkweed, they have to be careful not to fall into the blossoms -- if they do, they can become trapped in the flowers' sticky pollen-holding sacs (called pollinia) and expire. Nevertheless, these tiny bees have an advantage when feeding on nectar in flowers too small for large bees to enter. Ligated sfurrow bees are thus efficient pollinators of many species of wildflowers, among them bee balm, penstemon, goldenrod, bloodroot, rue anemone, dandelion, and violets.
Ligated furrow bees are blackish-brown with white bands of hair on their abdomens; dark eyes; and clear wings with brown veins. The females have pale scopal hairs on their hind legs and often appear lugging bright yellow saddlebags overflowering with pollen. Females have brownish black legs. Larger females tend to have disproportionately large heads. Females' mandibles and dark, and their antennae dark and medium-length. As shown in the photo strip here, males have yellow legs with dark markings on them; partly-yellow faces; and mandibles that are yellow and reddish-brown. The males' antennae are long and yellow mixed with reddish-brown.
Halictus ligatus (female)
Halictus ligatus (male)
Taxonomy of Halictus Furrow Bees
Order: Hymenoptera
Family: Halictidae (Sweat Bees)
Subfamily: Halictinae
Tribe: Halictini
Genus: Halictus
Species: Halictus Ligatus , Halictus confusus, Halictus rubicundus
A female ligated furrowbee on a coneflower, carrying "saddlebags" overflowing with pollen.
A female ligated furrow bee on an aster: female ligated sweat bees often appear in this arched posture as they forage for pollen.
Female ligated furrow bees have an indentation in the tip of the abdomen -- this is not always apparent, because the bees tend to curve their abdomens downward, hiding the last segment.
Confusing Furrow Bee
Halictus confusus
(Subgenus Seladonia)
1/5 - 1/3" (very small)
Confusing furrow bees belong to the subgenus Seladonia of the genus Halictus. Bees of this subgenus have greenish, bluish or brassy thoraxes and pale abdominal bands. Halictus confusus is found throughout the United States and appears in the park and Stone Barns from May through October.
Like bumblebees, confusing furrow bees are eusocial; their nests contain two generations of bees, a mother and her daughters, who work cooperatively, protecting and provisioning the nest and caring for larva after they hatch. Confusing sweat bees construct their nests in dry areas in a wide range of habitats. Their flight distance from their nests is fairly short – about 75 – 140 yards, and thus food sources must be in close range of where the bees settle.
Confusing sweat bees are common pollinators of strawberries, watermelons, peppers and tomatoes. These bees are considered broad generalists. In addition to being crop pollinators, they visit an array of important native wildflowers, among them, hemp dogbane, goldenrod, mountain mint and fleabane.
Identifying traits: These are small bees, under 1/3” in length. Their heads and thoraxes are dark bronze or greenish-metallic in color, and their abdomens are bronze with pale bands. Females have bronze faces and dark legs, dark mandibles and medium-length dark antennae
Males have vivid yellow-and-orange legs, and parts of their faces are also yellow (the mandibles, the labrum and a third of the clypeus, as shown in the photos strip here). The clypeus of the male Halictus confusus is protuberant, a trait that helps distinguish it from similar male bees. The antennae of male confusing furrow bees are predominantly dark and very long.
Halictus confusus (female)
Halictus confusus (male),: note the bee's protuberant yellow clypeus
A female confusing furrow bee with green-gold coloration on her head and thorax
Female confusing furrow bees have dark legs covered with pale hairs; the tips of their legs are often reddish. Their abdomens are bronze with bands of pale hairs.
Note the strong bronze-metallic coloring of the female bee's head and thorax.
Orange-legged Furrow Bee
Halictus rubicundus
(Subgenus Protohalictus)
2/5" (small)
Halictus rubicundus is an unusal bee species. Most bees are categorized as either social, eusocial or solitary. Social bees may form highly complex colonies organized into hierarchies of queens, workers and drones. Solitary bees build individual nests. Eusocial bees are in the middle – they build nests that may house more than one bee generation and that may include, for example, bees that have different tasks such as pollen gathering or caring for young. The social behavior of Halictus rubicundus varies depending on the climate. In warmer climates, it is eusocial, producing nests that contain small bee groups consisting of a reproductive female and her offspring. In cooler climates, the bees are solitary.
Halictus rubicundus usually dig nests in sloping or vertical bare ground, constructing 5-7 cells in which to lay eggs. The bees leave a tell-tale small pile of excavated dirt called a “tumulus” outside their nest entrances. Halictus rubicundus nests appear singly and in aggregations.
Halictus rubicundus are fairly large for sweat bees – both males and females are about 2/5”. The bees are dark brown with sharply-defined white bands on the first four segments of their abdomens (T1-T4). Females have dark faces, and their legs are reddish-orange with pale yellowish hairs. Female Halictus rubicundus also have pale hairs on their faces. Their wings are reddish.
Males have yellow legs with black and reddish markings, and partly yellow faces. Males, notably, have predominantly black or brown mandibles. This helps distinguish them from male ligated furrow bees. shown above, which have yellow and reddish mandibles.
Halictus rubicundus are found throughout the northern hemisphere, in northern Asia, Europe and America. These bees are considered "highly polyetic" and are documented pollinators of an astounding variety of commercial crops including apples, plums, blueberries, melons, squash, strawberries, potatoes and sunflowers. They also pollinate garden flowers and wildflowers from several plant families; they forage on wild plants as diverse as chokecherry, winterberry, spreading dogbane, fleabane, lupine, allium, delphinium, New Jersey tea, and California poppies. The male bee shown here was feeding on mountain mint. The female was foraging in mid-April on a variety of flowering plants in a pastured area of the park's Rockwood Hall section.
A female Halictus rubicundus
A male Halictus rubicundus
A female Halictus rubicundus
Alternate view of a female Halictus rubicundus
Tip of abdomen of female Halictus rubicundus
Dark, Striped Lasioglossum Sweat Bees
Leathery Sweat Bee
Lasioglossum coriaceum
(Subgenus Lasioglossum)
1/3" -1/2" (medium-sized)
Dark Lasioglossum with banded abdomens are common throughout the spring and summer in the park and Stone Barns. Such bees typically fall into one of three subgenera - - the redundantly named subgenus Lasioglossum; the subgenus Sphecodogastra; and the subgenus Evylaeus. Examples of these three groups are shown here.
Lasioglossum coriaceum is a member of the subgenus Lasioglossum (as well as the genus Lasioglossum). This species is notably large for a sweat bee -- nearly 1/2" long. The bee has a slender, elongated black abdomen ringed with well-defined bands of white hair; dark legs; and dark wings. Males have have exceptionally large jaws and distinctive yellow masks on their faces. Other nuanced traits (a broad cheek and dark distitarsi) help identify females of this species.
These bees are broad generalists and appear in August in the park and at Stone Barns on numerous flowering plants. Leathery sweat bees show a preference for small-blossomed plants such as goldenrod, Queen Anne's lace, catmint and other mints. They are documented pollinators of a variety of crops, including apples, melons, blueberries, strawberries and caneberries.
A male leathery sweat bee (Lasioglossum coriaceum)
This is a male Leathery sweat bee of the subgenus Lasioglossum -- a one-half inch, slender, dark bee with a black abdomen striped with bands of pale hair.
The male leathery sweat bee (Lasioglossum coriaceum) has a dark head, thorax, legs and antennnae.
The male bee has striking features: large jaws and a distinctively-shaped yellow mask.
Quebec Lasioglossum
Lasioglossum quebecense
(Subgenus Sphecodogastra)
1/4" (small)
The Quebec Lasioglossum (Lasioglossum quebecense). belongs to the subgenus Sphecodogastra. This bee is barely 1/4" long and is dark with faint white stripes banding its abdomen. Its head and thorax appear matte-black to the naked eye. Male Lasioglossum quebecense have partially yellow faces and legs and sometimes sport red abdomens instead of black ones.
The above entry in this guide explains that striped Halictus and Lasioglossum sweat bees can be distinguished because on the latter, the pale hairs banding bees' abdomens appear on the inner edges of the abdominal segments. Lasioglossum quebecense are an exception to this rule. As shown in the photo strip here, on the Quebec Lasioglossum, pale hairs band both the top and bottom of each striped abdominal segment.
Quebec Lasioglossum are pollinators of cranberries, cucumbers and cherries, as well as a vast array of flowering native and garden plants. The bee pictured here appeared in May in the park, nectaring on the woodland ephemeral known as spring beauty.
Sweat bees of the Lasioglossum subgenus Sphecodastra favor sandy, stony areas as nest sites. They produce one generation per year: females build nests consisting of a cluster of 12 to 20 cells constructed close to the soil surface. The bee's offspring hatch about 45 days later. After mating, the males die off, and the females dig deep tunnels in which to hibernate over the winter. In the spring, the female bees lay eggs and the cycle recommences.
A Female Quebec Lasioglossum (Lasioglossum quebecense)
A female Quebec sweat bee. This bee defies the general rule -- Lasioglossum quebecense sweat bees have pale hairs that encircle both the top and bottom of each banded abdominal segment. These bees are members of the subgenus Sphecodogastra.
Quebec sweat bees have matte-black heads and thoraxes.
The thorax of a Quebec sweat bee is covered with minute punctures.
Evening Primrose Sweat Bee
Lasioglossum oenothera
Subgenus Sphecodogastra)
3/10" (small)
The evening primrose sweat bee (Lasioglossum oenotherae), another member of the subgenus Sphecodogastra. is a relatively large dark sweat bee, about 1/3" long, with weakly-defined pale abdominal bands, a broad head, and long jaws with reddish tips. Male Lasioglossum oenotherae have yellow-and-black faces and legs.
This sweat bee species specializes on Oenothera, a flowering plant commonly known as evening primrose, which belongs to the plant family Onagraceae,. Oenothera is native to the Americas, although the evening primroses most often seen in New York wild lands are escaped yellow garden varieties that have naturalized in grassy areas. Evening primrose sweat bees have been documented feeding on goldenrod as well.
Female evening primrose sweat bees have conspicuous pale scopal hairs on the middle sections of their hind legs, while their hind femurs are less hairy. According to entomologist Charles D. Michener, the scopae of Lasioglossum oenothera are specially adapted for gathering nutrients from members of the plant family Onagraceae, whose pollen is webbed and thus sticks well to itself.
The bee shown here appeared pollinating an escaped garden Oenothera in a pasture area of the park's Rockwood Hall. Several female Lasioglossum oenotherae congregated on each of the plant's blossoms. Many of them entered flowers that had not yet opened, in order to gather pollen directly from the closed buds. Anecdotal information suggests that this behavior is typical of this species. Early in the season, females may appear in the evening, but thereafter they tend to be found pollinating evening primrose only in the mornings.
A female evening primrose sweat bee (Lasioglossum oenothera)
This is a female evening primrose sweat bee -- also a member of the subgenus Sphecodogastra. These bees have dark abdomens banded by faint stripes of pale hair.
Bees of the species Lasioglossum oenothera specialize in pollinating the yellow flowers of evening primrose.
An evening primrose
Lasioglossum (Evylaeus) Dark Sweat Bee
(Subgenus Evylaeus sensu lato)
1/6' - 1/4" (very small to small)
Lasioglossum sweat bees of the subgenus Evylaeus are ground nesters that construct nests with turrets at the entrances and tightly-clustered brood cells. According to entomologist Charles D. Michener, the Evylaeus subgenus includes species with more complex social behavior than the Dialictus sweat bees shown directly below.
Many Lasioglossum (Evylaeus) are generalist pollinators. These bees are frequent visitors to the agricultural fields of Stone Barns and to native woodland flowers in the park.
Lasioglossum (Evylaeus) tend to be dark and to lack metallic coloration. The male Lasioglossum (Evylaeus) shown at bottom right is fairly typical of its subgenus. It is a non-metallic black and so long and slender as to seem antlike. The bee is also quite small - barely 1/5 inch in length. Pale hairs on the bee's abdomen are invisible to the naked eye.
To the naked eye, Lasioglossum (Evylaeus) are similar in appearance to other varieties of small dark bees appearing in this guide, particularly small carpenter bees. Minute inspection is often necessary for identification.
Lasioglossum Subgenus Evylaeus sensu lato
A male Lassioglossum (Evylaeus sensu lato) sweat bee
Aear view of a male Lassioglossum (Evylaeus sensu lato): note the bee's elongated abdomen.
EXAMPLES OF DARK METALLIC SWEAT BEES - LASIOGLOSSOM (DIALICTUS)
DARK METALLIC SWEAT BEES
Lasioglossum (Dialictus)
Lastioglossum of the subgenus Dialictus are typically metallic, with a dark green, bronze or blue sheen. The bronze sweat bee shown here is a typical example. Lasioglossum (Dialictus) are generally ground-nesters that build nests with loose clusters of brood cells. They tend to be generalist pollinators.
Hairy Metallic Sweat Bee
Lasioglossum pilosum
1/6' - 1/4" (very small to small)
Among the most easily recognized Lasioglossum (Dialictus in our area is the hairy metallic sweat bee (Lasioglossum pilosum), shown here. This bee is distinctive because it has an abdomen thickly covered with tan hairs and a bright bronze-gold thorax. To the naked eye, the bee appears pale gold and fuzzy. Hairy metallic sweat bees are pollinators of milkweeds, thistles and wild roses, among many other flowering garden and native plants. They also pollinate stone fruits as well as melons, berries and apples. The Lasioglossum pilosum shown here was discovered feeding on a wild aster on the edge of a sunlit trail of Rockefeller State Park Preserve in August.
Epaulette Metallic Sweat Bee
Lasioglossum tegulare
1/6' - 1/5" (very small)
A second example of a metallic Lasioglossum (Dialictus) sweat bee is Lasioglossum tegulare. This is a very small, slender bee that looks nearly black to the naked eye. Females of this species are 1/5” or smaller; males, like the one shown here, are closer to 1/6”. The bee’s head, thorax and abdomen have a coppery-bronze sheen. Pale hairs sprout from the bee’s face and cheeks, and sparse bands of longish white hair ring some of the bee’s abdominal segments. This species’ name, tegulare, derives from tegula, the part of a bee where the wing attaches to the insect’s body. On this species, the tegula is irregularly shaped. (Tegula are usually oval and symmetrical, but on this bee, the inner edge of the tegula is flattened or slightly concave with a slight inward-pointing projection at the back. This nuanced trait exemplifies the subtleties involved in distinguishing one Lasioglossum species from another.)
This miniscule sweat bee is a pollinator of apples, blueberries, caneberries, melons and strawberries. Lassioglossum tegulare are also pollinators of many native wildflowers, among them viburnum, swamp milkweed, goldenrod, fleabane, bee balm, sneezeweed, yellow indigo, wild rose, fringed loosestrife and buttercups. The male bee shown here was found feeding on goldenrod in September.
Experienced Lasioglossum
Lasioglossum resembling true L. versatum (=rohweri)
1/5' - 1/4" (very small)
Many species of Lasioglossum (Dialictus) are nearly impossible to differentiate from one another with the naked eye. An example is Lasioglossum (Lasioglossum versatum). The bee shown at center right -- tentatively identified by an expert as Lasioglossum (Dialictus) resembling true L. versatum (=rohweri) -- has a dark greenish-bronze metallic head and thorax and a brownish-black abdomen covered with fine pale hairs. These characteristics are shared by many Dialictus, and species identification usually hinges on minute inspection with a microsscope. Lasioglossum versatum forages on a a broad range of garden flowers, such as chrysanthemums, black-eyed Susans, fleabane, Queen Anne’s lace, dandelions, clover, thistles and viburnum. This small bee is also a pollinator of such crops as melons, strawberries, blueberries and caneberries. The bee shown here was found foraging on goldenrod at Stone Barns in August.
Lasiglossum (Dialictus) sweat bees often have the metallic gold-bronze coloration shown here.
Head of a metallic Lasioglossum (Dialictus) - both the head and thorax of this sweat bee are a shiny gold-bronze.
This is a female hairy metallic sweat bee (Lasioglossum pilosum). A member of the subgenus Dialictus, this species is metallic bronze and covered with golden and tan hairs.
Hairy metallic sweat bees have metallic-bronze thoraxes covered with hairs that may appear bright gold.
Head of a hairy metallic sweat bee
The bee's abdomen is thickly covered with tan hairs.
A male Lasioglossum tegulare (Subgenus Dialictus)
A tentatively identified female Lasioglossum versatum (Subgenus Dialictus)
PHOTO CREDITS: All photos and text © Copyright 2014-2017 Paula Sharp and Ross Eatman, unless otherwise noted. All rights reserved. If you wish to use any of the photographs here for educational or other purposes, please read permissions page.
REFERENCES: For a comprehensive list of references used in compiling this guide, click here:
