Identification Guide to the Megachilidae Genera of Eastern North America

Chunky Bees that Carry Pollen Under their Abdomens: A Guide to their identification in Eastern North America

Acknowledgements
This presentation has been put together by a consortium of North American bee biologists
This presentation has developed over many years and the original web picture acknowledgements were lost, if you see one of your pictures let us know and we will add your picture credit
Correspondence can be sent to Sam Droege at sdroege@usgs.gov

Format
Each Genus has an information page followed by a page of illustrations and a map of the distribution of Eastern North American species; western populations of Eastern species are shown, but the Western species are not mapped.
The number of Eastern species are listed at the top of the page

Anthidiellum – 2 species
Anthidium - 4
Dianthidium - 3
Paranthidium - 1
Stelis - 12
Trachusa - 5
Hoplitis - 8
Osmia - 28
Ashmeadiella - 2
Chelostoma - 3
Heriades - 3
Coelioxys - 24
Lithurgus - 3
Megachile - 40

Anthidiellum
Quite small, less than half the size of a honeybee
Fast flying, likes legumes, dry fields
Front of the mesepisternum (side facing the head) divided from the outward facing side by a sharp edge or carina
Unique in that the scutellum projects over the metanotum and propodeum as a THIN squared- off shelf, other species project a small amount but not as much and the edge is rounded over
Unique in that the sub-antennal sutures bend outwards
Similar Genera: Anthidium, Dianthidium, Paranthidium, Stelis, Trachusa

2 Species, small, fast, likes legumes and dry sites

Anthidium
2 common introduced species, 2 rare native species, most about the size of a honeybee or slightly smaller
Unique among genera listed below in that it has no pad or arolium between the tarsal claws at the ends of the legs
Female unique in that it has 5 or more teeth on the mandible
Similar Genera: Anthidiellum, Dianthidium, Stelis, Trachusa, Paranthidium

Some common introduced species 4 Species

Dianthidium
A bit smaller than a honey bee, uncommon to rare
Has a small hollowed out area or fovea behind the spiracle on the rear face of the propodeum about the size of the spiracle
Front of the mesepisternum (side facing the head) divided from the outward facing side by a sharp edge or carina
Similar Genera: Anthidium, Paranthidium, Stelis, Anthidiellum, Trachusa

Uncommon to rare 3 Species

Paranthidium jugatorium
Rare, but known to occur abundantly in at least one arboretum
Front of the mesepisternum (side facing the the head) NOT divided from the outer facing side by a sharp edge or carina
Front and middle tibia without a spine, the outer tip of tibia with a curved, transverse, projecting lamella, behind which the surface is shining and scoop-like
Margin of tip of mandible straight and at an oblique angle to outer margin, about half as long as mandible
Similar Genera: Anthidium, Anthidiellum, Dianthidium, Stelis, Trachusa

Uncommon, garden exception

Stelis
Rare, one quarter to two-thirds the size of the honeybee
Nest parasites on Osmia, Megachile, Heriades, and Ashmeadiella and thus have no scopa on the underside of their abdomens like most other Megachilidae species
A variety of body types from very bright and colorful like Anthidium to dark and small like Heriades, some of these groups have been assigned Genus status in the past
Similar Genera: Trachusa, Anthidium, Anthidiellum, Dianthidium, Paranthidium, Heriades, Ashmeadiella, Chelostoma

Uncommon, parasites of Hoplitis, Osmia, Heriades, Ashmeadiella 12 Species

Trachusa
Uncommon to rare, about the size of a honeybee
Front edge of scutum clearly raised above the pronotal collar
Similar Genera: Stelis, Anthidium, Anthidiellum, Paranthidium, Dianthidium

Uncommon, southern, 5 species

Hoplitis
Relatively common dark brown, spring to early summer species
Parapsidial line on scutum long and similar to most other bee species
Males often have modified antennae with hooked ends or expanded segments
Similar Genera: Osmia, Heriades, Chelostoma, Ashmeadiella

Relatively common 8 species

Osmia
Common spring to early summer species, ranging from one-third the size of a honeybee to slightly larger
The majority of species are dark blue (often appearing black in the field) with a few that are brown, black, and one rare bright green one
The parapsidial line of the scutum contracted to a line that is usually only 2-5 pit diameters long and is often difficult to find amidst the surface pitting
Differentiating males is particularly tricky as many of the best characters are on the underside of the abdomen and often hidden by retracted segments and curled abdomens
Similar Genera: Hoplitis, Ashmeadiella, Heriades, Chelostoma

Common, spring, hole-nester, 28 species

Ashmeadiella
Rare, about one quarter the size of a honeybee
Front of the mesepisternum (side facing the head) divided from the outer facing side by a sharp edge or carina
Similar Genera: Heriades, Chelostoma, Stelis, Osmia, Hoplitis

Rare Small 2 species

Chelostoma
Rare to Locally Common, Small, about one-quarter the size of a honeybee
Skinnier and more elongate than the other Megachilid genera
Head unusually long
2 introduced species now spreading slowly from New York and Ontario and pollen specialists on Campanula , 1 native species which is a specialist on Mock Orange ( Philadelphus )
Similar Species: Heriades, Ashmeadiella, Osmia, Hoplitis, Stelis

Tiny, elongate, 3 species, 2 introduced

Heriades
Uncommon, small, about one quarter the size of a honeybee
Has a very sculptured appearance with large diameter pits throughout
Upper surface of Propodeum is formed of a narrow row of open square cells defined by prominent raised lines
Unique within Megachilidae in that the portion of T1 that faces the thorax is hollowed out and surrounded by a raised line or carina
Similar Genera: Ashmeadiella, Chelostoma, Hoplitis, Osmia, Stelis

Tiny, uncommon to locally common, 3 species

Megachile
Moderate to large, common particularly in the summer, from about half to 1.5 times the size of a honeybee
Most are black with thin white bands of hair on their abdomens
Males of some species have greatly expanded front tibia
Cutting edges of the mandibles often very useful in females but best seen by pulling open mandibles when specimens are fresh
Unlike genera listed below, has no arolium or pad between the tarsal claws of the legs
Similar Genera: Lithurgus, Coelioxys

Common in all open environments 40 species

Coelioxys
Regular, but sparsely distributed, primarily out in the summer and early fall, most about the size of a honeybee
Nest parasites of Megachile and thus the females have no pollen carrying hairs under their abdomens
The axillae, which normally hug the edge of the scutellum, flare outwards and the shape of their tips are often diagnostic
Females have long, pointed abdomens, the shape of which is often unique
Males have an odd cluster of pointed or flattened projections and spines at the end of their abdomen, the pattern of which is also often unique
Similar Genera: Megachile, Lithurgus

Parasite of Megachile, pointed rear, arolia, no scopa 24 Species

Lithurgus
Rare to locally common
2 native species are cactus ( Opuntia ) pollen specialists
The introduced species, L. chrysurus , is spreading slowly out of central New Jersey and eastern Pennsylvania and is a knapweed ( Centaurea ) pollen specialist and can be abundant when found
Often overlooked as Megachile (particularly males) but has an arolium or pad between its tarsal claws
Females all have a diagnostic and very prominent projecting flange between the clypeus and the antennal bases
Both males and females have a 3-lobed tip to the mandible

Rare, 2 cactus specialists, 1 introduced

Resources
Species lists, Identification Guides, and Maps for genera and species are available at:
http://www.discoverlife.org/20/q?search=Apoidea
A guide to the genera of the bees of Canada is available at:
http://www.biology.ualberta.ca/bsc/ejournal/pgs_03/pgs_03.html
Mitchell’s 1960’s book on the bees of the Eastern United States is available as a series of pdf files at:
http://insectmuseum.org/easternBees.php
A slightly out of date guide to the identification of the genera of ALL of North America is available at:
http://www.knoxcellars.com/Merchant5/merchant.mvc?Screen=PROD&Store_Code=KCNP&Product_Code=BGNA&Category_Code=BL

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Identification Guide to the Megachilidae Genera of Eastern North America

by Sam Droege

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Identification Guide to the Megachilidae Genera of Eastern North America Presentation Transcript