A silky agapostemon female

 

 

 

 

SWEAT BEES.   Halictidae, tiny nonaggressive "sweat bees," comprise one of the seven bee families in the 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 (genuses) 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 distinct sweat bee genera that can be grouped roughly by their salient characteristics:  (1)  iridescent green bees (Agapostemon, Augochlora, Augochloropsis and Augochlorella); and (2) bees that are dark in color, usually with striped abdomens (Halictus and Lasioglossum).  Part 1 of this guide's sweat bee section focuses on green metallic sweat bees.

Bi-colored Agapostemon

Agapostemon virescens -  2/5"  (medium-small)

Bi-colored Agapostemons are jewel-like bees with metallic green heads and thoraxes and striped abdomens. They build nests consisting of deep vertical burrows in sloping soil and banks. The bees keep their nests well-hidden under leaves and grass, but occasionally you may observe one of these bees suddenly disappear into a hole in the ground. 

 

Also known as virescent green metallic bees, bi-colored Agapostemons are considered "gregarious" -- that is,  they band together in communal nests, with each female provisioning her own burrow.  The nests are usually protected by a guard bee that blocks the entrance with its head.  This provides the bees' eggs and offspring with better protection against cuckoo bees and other predators than nests maintained by solitary bees.  According to the National Audubon Society Field Guide to Insects and Spiders, bi-colored Agapostemons work cooperatively; bees entering the nest carrying pollen are given right-of-way over those trying to leave, and multiple bees in the nest work to restore entrance holes as they crumble. Bi-colored Agapostemons pass more than one generation in a single summer, and thus, they are visible from the beginning to the end of the warm season in New York. 

 

Bi-colored Agapostemons are polylectic -- that is, they feed on a variety of plants rather than specializing on a single kind.  These bees appear in the park's gardens, meadows and woodland paths in mid-spring and remain through mid-October, foraging for nectar on such plants as coneflowers, coreopsis, mountain mint, Joy Pye weed, goldenrod and New England asters. They are one of a few species of bees that feed on the nectar of native American white water lilies, which bloom in the park's Swan Lake during the summer.

 

In addition to being efficient pollinators of wildflowers, bi-colored Agapostemons are key pollinators of sunflowers and legumes.  Throughout the summer, they are regular visitors to the sunflower plantings in Stone Barns' vegetable fields.

 

Identifying Traits:  Bi-colored Agapostemons can be identified by their shiny green heads and thoraxes.  Female Agapostemons' abdomens are striped with bands of white hairs.  The female bees frequently carry large caches of yellow pollen on their hind legs, as shown in the photos at right.  Male bi-colored Agapostemons have abdomens striped with yellow bands, yellow legs with black markings, and partly yellow faces and mandibles.  Male bi-colored Agapostemons may be tricky to differentiate from  male Agapostemons of other species.  As shown in the photostrip at right, a distinguishing trait of the male bi-colored Agapostemon is that the bee's sternum is mostly black.  (The sternum is the underside of the bee's abdomen. )  Another distinctive trait is that the trochanter (the top segment) of the male bee's hind leg is iridescent green.

 

Taxonomy of Agapostemon Sweat Bees

Order:   Hymenoptera
Family:   Halictidae  (Sweat Bees)
Subfamily:   Halictinae
Tribe:  Halictini
Genus:   Agapostemon (Metallic Green Bees)
Subgenus:  Agapostemon
Species:  Agapostemon virescens

A bi-colored  agapostemon male

A bi-colored  agapostemon female

All photos (c) 2014 - 2016 Sharp-Eatman Nature Photography

Silky Agapostemon

Agapostemon sericeus –  .4" - .45"  (medium-small)

These stunning bees pollinate a variety of fruit crops, including melons, apples, blueberries, cranberries and blackberries.  Silky Agapostemons also visit a multitude of garden flowers and wildflowers, among them rhododendrons, catmint, asters, yarrow and goldenrod.  In early spring, these bees can be found pollinating the wild blackberries that abound in the park. In late spring and early summer, silky Agapostemons are avid visitors of orange milkweed in the gardens and fields of Stone Barns and the park. 

 

Female silky Agapostemons are industrious pollinators.  They are fast fliers and, when collecting pollen, they alight briefly on a flower before zipping on to the next.  Females carry  pollen on their hind legs.  Males tend to fly more slowly and rest longer on flowers, looking for mates.

 

Silky Agapostemons are solitary and build their nests in the ground. They are sometimes preyed on by the black-and-red cuckoo bee, Sphecodes prosphorus, which steals into the solitary silky Agapostemon nests and lays its own eggs there.  When the cuckoo bee's eggs hatch, they kill off the Agapostemon's young and eat the food stored for them. 

Identifying Traits:   The heads, thoraxes and abdomens of female silky Agapostemons are solid iridscent yellowish-green.  The females have dark legs covered with long pale-gold hairs.  Male silky Agapostemons have green heads and thoraxes, but their abdomens are striped yellow-and black.  Their legs are yellow with with black markings.  Traits helpful in distinguishing silky Agapostemons from other green sweat bees are noted below and in the photos at right. 

 

Hand characteristics of Females:  Silky Agapostemon females are often confused with the green metallic sweat bees of the Augochlorini tribe featured below on this guide page.  Some traits that are helpful in distinguishing female silky Agapostemons are:   (1)  They are much heftier than the three green metallic bees shown below -- the silky Agapostemon's abdomen is broader and bulkier, and its body is notably longer (nearly half an inch, compared to Augochlora pura  at .31"; Augochlora metallica at .35"; and Augochorella aurata at .21").  (2) As shown in the photostrip at right, female silky Agapostemons' thoraxes have a rough texture, and their abdomens have three white hairbands, the second of which tends to be the widest.  (3) The Xerces Society's Guide to Attracting Native Pollinators notes that the easiest way to tell female Agapostemons from the Augochlora pura bee directly below is to look at the rear of the thorax:  the Agapostemon's is flat and edged by a curved ridge; the Augochlora pura bee's, by contrast, is rounded and ridgeless.  (4) The flight pattern of the female silky Agapostemon is also distinctive -- a jagged series of fast figure eights -- and it tends to come to rest on the tops of the flowers.   Augochlora pura and Augochloropsis metallica green sweat bees, by contrast, tend to curl their bodies around flower parts and to hang from below or from the sides of flowers.

 

Hand Characteristics of Male Silky Agapostemons:  Male Silky Agapostemons  are much less frequently seen in the park and Stone Barns than  females.  Male silky Agapostemons can be very difficult to differentiate with the naked eye from other species of the genus Agapostemon. One way to tell male silky Agapostemon males from bi-colored Agapostemon males is that the underside (sternum) of a bi-colored Agapostemon's abdomen is distinctly blacker.  (See photos in the above entry on bi-colored Agapostemons.)   A male silky Agapostemon has yellow spots on the sixth segment of its sternum.

 

Taxonomy of Agapostemon  Sweat Bees

Order:   Hymenoptera
Family:   Halictidae  (Sweat Bees)
Subfamily:   Halictinae
Tribe:   Halictini
Genus:   Agapostemon (Metallic Green Bees)
Subgenus:   Agapostemon
Species:   Agapostemon sericeus

A silky  agapostemon  female

A male silky  agapostemon  

All photos (c) 2014 - 2016 Sharp-Eatman Nature Photography

The Bee Tribe Augochlorini

 

The Greek prefix  augochlor-  means "intensified gold- green," a coloration shared by all three of the  Augochlorini tribe bees shown below on this guide page.  According to Charles D. Michener’s The Social Behavior of the Bees, the tribe Augochlorini consists of bees that are typically brilliant green (but sometimes purple, blue, brassy, red or black); and that live predominantly in Central and South America.  Only a few species, divided into three genera (genuses) --  Augochlora,  Augochloropsis,  and Augochlorella -- range into the United States and Canada.  Bees of the Augochlorini tribe are generally solitary, and tend to build nests in soil or, less commonly, in rotted wood.  Some form large aggregations, constructing ground nests in clumps linked together by earthen connections or rootlets.  

Auguchlorini vs. agapostemons.  Bees of the augochlorini tribe tend to be smaller generally than the agapostemons shown above.  The augochlorini shown below lack the agapostemon's sexual differentiation as well -- male augochlorini resemble females and, like them, have green, rather than striped abdomens.  

Augochlora Pura Green Metallic Bee 

Augochlora pura  –  3/10"  (small)

Augochlora pura green metalllic bees are solitary sweat bees that prefer woodland areas and build nests under bark in rotting trees.  They cobble their nests together using bits of dirt and debris found under the bark.  The female bee at right was discovered racing in and out of tunnels and holes in a fallen log near the park's Eagle Hill Trail.  Dozens of other Augochlora pura nested around her in the same log, looking like living emeralds scurrying in and out of the bark.

 

Augochlora pura bees emerge in early spring, feeding on pollen from blossoming maple trees.  Augochlora pura become highly visible in the park in May, pollinating spring wildflowers and the tree peonies in the park's Peony Monument garden.  In the summer, the bees can be seen visiting orange butterfly milkweed, wild phlox and goldenrod in sunny areas of the park and pollinating squash and a variety of flowers in Stone Barns' vegetable fields and gardens.  Augochlora pura green metallic bees continue to pollinate the park's late-blooming asters and goldenrod through mid-fall.

 

Identifying Traits:   These striking bees look like flying emeralds.   Augochlora  pura have brilliant green heads, thoraxes and abdomens covered with minute whitish hairs.  Their heads are roughly hexagonal, their antennae are black, and their legs and wings are brown.  Females carry pollen on their hind legs and have distinctive black mandibles.  Augochlora pura sweat bees occasionally appear with a predominantly golden-bronze coloration. An identifying characteristic of this species is these little bees' tendency to curl themselves around small flower parts as they sip nectar from plants, as shown in the photos here. 

 

Augochlora pura bees can be distinguished from other green metallic bees in part by minute inspection of three traits:  (1)  an Augochlora pura bee's tegulae (where the wings attach) are dark and oval in shape; (2) the marginal cell of an A. pura bee's wing is truncate; and (3) the female bee's face has distinctive "epistomal lobes".   These traits are shown in the photostrip at right.

 

Taxonomy of Augochlora Pura Sweat  Bees

Order:   Hymenoptera
Family:   Halictidae  (Sweat Bees)
Subfamily:   Halictinae
Tribe:   Augochlorini

Genus:   Augochlora               

Species:  Augochlora pura

Augochlorella Aurata Sweat Bee 

Augochlorella aurata
1/5”  (.21")  (very small)

Augochlorella aurata sweat bees are the smallest of the three species of the tribe Augochlorini  found in Rockefeller State Park Preserve.  These tiny bees are usually green -- ranging from pale-green to yellow-green to coppery-green.  Male Augochlorella aurata show particularly great variation in color, and sometimes appear with a reddish or pink sheen (like one of the bees shown in the photo strip at right). 

 

Augochlorella aurata sweat bees nest in partly-bare areas of flat or gradually sloped ground.  In his seminal work, The Social Behavior of the Bees, the renowned entomologist Charles D. Michener wrote extensively on the nesting behavior and life cycle of Augochlorella aurata (known then under the name Augochlorella striata).  Augochlorella aurata are considered “primitively eusocial” bees.  They have a yearly life cycle split into spring and summer phases.  In the first spring “foundress phase,” the bees construct an underground nest and provision it for 6-8 male and female offspring.  When the young emerge, the males leave the nest, never to return.  The females remain in the nest as workers.  In the second phase, the original “foundress workers” cease working and the new workers take over and provision the nest for a second brood of 8-13 males and females called reproductives.   When this second brood hatches in late summer, the males and females mate. The males die and the inseminated females overwinter.  To stay warm, the females dig downward into the earth from the lowest parts of their nests.  They emerge in spring to complete the colony’s life cycle.

 

Augochlorella aurata social behavior shows flexibility, however.  The bees' nests are sometimes established by a single foundress that dies off during the worker phase, and which is replaced by a single “replacement queen” from the first brood.  In such instances, orphaned colonies are considered “parasocial” .  (Only colonies that retain the original queen throughout the second season are called “eusocial”.)  Parasocial colonies allow for more diversity of genetic material in the hive.

 

Augochlorella aurata bees are broad generalist pollinators that visit a seemingly endless range of wildflowers.  In the park, they are likely to be spotted foraging  on dogbane, fleabane, mountain mint, wild roses and goldenrod.  The pink male bee shown here was found feeding on goldenrod in mid-August on a sunny park trail.  The green female bee was discovered nectaring on wild carrots in Stone Barns' cut-flower fields in early September.  Augochlorella bees are also common pollinators of apples, caneberries, strawberries, tomatoes and watermelons.

Identifying Traits:   As noted, these bees are the smallest of the species shown on this page -- the Augochlorella aurata  shown here were all 1/5" or smaller.  Other distinctive traits of this species include the bee's occasional pinkish-copper coloring and its narrow vertex (the top of the head behind the bee's ocelli or three small eyes).  The marginal cell of an Augochlorella aurata's wing is pointed (as shown in the photo strip at right); this helps distinguish this species from the Augochlora pura sweat bee shown higher up on this page.

 

Taxonomy of Augochlorella Aurata  Sweat Bees

Order:   Hymenoptera
Family:   Halictidae  (Sweat Bees)
Subfamily:   Halictinae
Tribe:   Augochlorini

Genus:   Augochloraella             

Species:  Augochlorella aurata

A golden green Augochlorella aurata

An Augochlorella aurata with coppery-pink coloration

An Augochlora pura sweat bee emerging from under the bark of a fallen tree

An Augochloropsis metallica male

Augochloropsis Metallica 

Augochloropsis metallica –  .35”  (small)

Augochloropsis bees are believed to have originated 16 million years ago and to have entered temperate North America 4 million years ago.  There are only three species of this genus in the United States. The bee shown here, Augochloropsis metallica , is found as far north as Canada and as far south as Texas.  

 

Augochloropsis metallica bees are solitary and nest in the ground. They visit an enormous range of flowering plants and are important in helping to maintain wildflower floral diversity.  They are documented pollinators of blueberries, caneberries and members of the melon and squash families.  These bees are far less common in the park than the other green metallic sweat bees shown on this guide page.  The bee featured here was found feeding on goldenrod in August on a sunlit park trail.

 

Identifying Traits:  Augochloropsis metallica bees have brilliant yellow-green bodies and broad, roughly hexagonal faces with green eyes and dark antennae.  Their wings are light-colored or clear with reddish-brown veins. The legs of female Augochloropsis metallica bees are green and covered with pale hairs; the end segments of the bees' legs (called tarsi) are dark brown.  Males have predominantly green legs, and pale yellow tarsi.  On female bees, the labrum (the face part between the mandibles) is black; on males it is green.  


Distinguishing among green metallic sweat bees:

A feature common to members of the Augochlorini tribe is that they have hind tibia that are shorter than their combined tarsal segments. Augochloropsis metallica are larger than Augochlora pura and Augochlorella aurata and have broader abdomens that bell outward near the bottom.

 

Commentary by entomologist John S. Ascher at bug-guide.net highlights the following subtle traits that help distinguish Augochloropsis from other green metallic bees on this guide page.  (1)  Augochloropsis  metallica's pronotal lobe (located at the front of the thorax) has a pronounced ridge.  (2)  Augochloropsis metallica's tegula (where the wing attaches) is angled and metallic green.  The tegula ofAugochlorella aurata is reddish, while that of Augochlora pura is dark and oval.  These traits are shown in the photo strip at right.

 

 

 

Taxonomy of Augochloropsis Sweat Bees

Order:   Hymenoptera
Family:   Halictidae  (Sweat Bees)
Subfamily:   Halictinae
Tribe:  Augochlorini
Genus:   Augochloropsis

Species:  Augochloropsis metallica

All photos (c) 2014 - 2016 Sharp-Eatman Nature Photography

All photos (c) 2014 - 2016 Sharp-Eatman Nature Photography

All photos (c) 2014 - 2016 Sharp-Eatman Nature Photography

PHOTO CREDITS:  All photos and text © Copyright 2014-2016 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:

 

ID GUIDE TO WILD BEES - NEW YORK

SWEAT BEES PART I - GREEN METALLIC BEES

 8-23-15