Megachile

Taxonomy

Overview

Megachile is a diverse genus that includes species with a wide range of body forms, although they generally exhibit a stocky build and robust head. They range in body length from 5–21 mm (Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).). Most Megachile have nonmetallic black bodies with pale apicalapical:
near or at the apex or end of any structure
bands of hair on their tergaterga:
the segments on the top side of the abdomen, often abbreviated when referring to a specific segment to T1, T2, T3, T4, T5, T6, or T7
, although some species may lack hair bandsbands:
usually referring to bands of hair or bands of color that traverse across an abdominal segment
or have yellow to red hair (Michener 2007Michener 2007:
Michener, C.D. 2007. The Bees of the World (2nd ed.). Johns Hopkins University Press, Baltimore and London, 953 pp.).

Diversity

Megachile contains over 1520 species in 53 subgenera worldwide; 140 species in 18 subgenera occur in the U.S. and Canada (Gonzalez 2013Gonzalez 2013:
Gonzalez, V.H. 2013. Taxonomic comments on Megachile subgenus Chrysosarus (Hymenoptera: Megachilidae). Journal of Melittology 5: 1ndash;6.; Trunz et al. 2016Trunz et al. 2016:
Trunz, V., L. Packer, J. Vieu, N. Arrigo, and C.J. Praz. 2016. Comprehensive phylogeny, biogeography and new classification of the diverse bee tribe Megachilini: Can we use DNA barcodes in phylogenies of large genera? Molecular Phylogenetics and Evolution 103: 245ndash;259.; Praz 2017Praz 2017:
Praz, C.J. 2017. Subgeneric classification and biology of the leafcutter and dauber bees (genus Megachile Latreille) of the western Palearctic (Hymenoptera, Apoidea, Megachilidae). Journal of Hymenoptera Research 55: 1-54.).

Diagnostic characteristics

(modified from Michener 2007Michener 2007:
Michener, C.D. 2007. The Bees of the World (2nd ed.). Johns Hopkins University Press, Baltimore and London, 953 pp.)

• Arolia absent on all legs.
• Axilla axilla:
  the triangular or rounded point on the thorax where thoracic muscles meet the forewing of an insect
  rounded or straight.
• Colored maculations entirely absent.
• Pronotal lobes carinatecarinate:
  having keels or carinae
  , or at least with weak transverse ridge.
• Scutellum scutellum:
  shield shaped plate behind scutum
  without laterallateral:
  relating, pertaining, or attached to the side
  teeth.
• Stigma stigma:
  a pigmented/ thickened spot on the costal margin of the forewing, usually at the end of the radius(Greek, stigma= mark)
  over twice as long as broad.
• Tarsal claws simple or bifidbifid:
  divided into two branches; forked
  .
• Female clypeusclypeus:
  a section of the face below the antennae, demarcated by the epistomal sutures
  highly modified.
• Female mandiblemandible:
  bee teeth, so to speak, usually crossed and folded in front of the mouth
  with 3 to 5 teeth.
• Female scopascopa:
  modified hairs for carrying pollen; often branched and dense hairs on the hind-leg, or on the ventral surface of the abdomen in Megachilidae
  present.
• Female T6T6:
  the segments on the top side of the abdomen, often abbreviated when referring to a specific segment to T1, T2, T3, T4, T5, T6, or T7
  without raised, impunctateimpunctate:
  marked with punctures or pits
  median ridge.
• Male T6T6:
  the segments on the top side of the abdomen, often abbreviated when referring to a specific segment to T1, T2, T3, T4, T5, T6, or T7
  with large preapicalpreapical:
  referring to a section of a bee that is physically found just before the outermost (or apical) end of the section or segment
  carinacarina:
  a clearly defined ridge or keel, not necessarily high or acute; usually appears on bees as simply a raised line
  , usually denticulatedenticulate:
  a small tooth-like projection
  and emarginateemarginate:
  a notched or cut out place in an edge or margin, can be dramatic or simply a subtle inward departure from the general curve or line of the margin or structure being described
  , sometimes reduced to two spines, rarely absent.

May be confused with

Some bees in the tribes Lithurgini and Megachilini look superficially similar to Megachile, but can be distinguished by a combination of the diagnostic characters above (Michener 2007Michener 2007:
Michener, C.D. 2007. The Bees of the World (2nd ed.). Johns Hopkins University Press, Baltimore and London, 953 pp.).

Known invasives

M. apicalis was introduced from the Old WorldOld World:
the part of the world that was known before the discovery of the Americas, comprised of Europe, Asia, and Africa; the Eastern Hemisphere
around 1930 and can be found on both North American coasts, although it is more widespread in the west (Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).). It effectively pollinates yellow starthistle (Centaurea solstitialis), an invasive noxious weed introduced from the Mediterranean, and may be assisting in its spread (Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).; Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). It may compete for nesting sites with native bees (Barthell et al. 1998Barthell et al. 1998:
Barthell, J.F., G.W. Frankie, and R.W. Thorp. 1998. Invader effects in a community of cavity nesting megachilid bees (Hymenoptera: Megachilidae). Environmental Entomology 27: 240ndash;247.).

M. chlorura is from the Philippines and was first reported in 1988 from Oahu, Hawaii. It has been noted to prefer Asteraceae (Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.).

M. concinna was indirectly introduced from Africa in 1940 to the West Indies and Mexico. It has a scattered, uncommon distribution through southern and western North America (Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).).

M. diligens was originally described from Hawaii in 1879; however, in the eastern hemisphere and Samoan islands other subspecies have been described, although the validity of such has been questioned (Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.). It may not be a native of Hawaii but a long ago introduced species from the South Pacific, possibly being introduced during Polynesian colonization of the Hawaiian archipelago. It can be found on Hawai’i, Kauai, Molokai, and Oahu islands (Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.).

M. ericetorium is a European and Asian species found in North America since 2000, and has been found in Ontario and New York (Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).). The status of establishment is currently unknown.

M. fullawayi was first collected in Hawaii in 1919 and was introduced from Southeast Asia. It can be found on Midway, Niihau, and Oahu islands (Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.).

M. gentilis is found on Kauai, Maui, Molokai, Oahu islands and is adventive from western North America, having been introduced sometime before 1899 (Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.).

M. lanata is native to China and India and was likely introduced indirectly to the continental U.S. sometime during the 18th or 19th century from northern South America or the West Indies (Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).). It is currently found in Florida and Hawaii.

M. rotundata, known as the alfalfa leafcutter bee, is widespread in the PalearcticPalearctic:
the largest biogeographic region; consists of Europe, Asia north of the Himalaya foothills, Northern Africa, and the northern and central parts of the Arabian Peninsula
and was accidentally introduced to the U.S. sometime before 1940 (Pitts-Singer and Cane 2011Pitts-Singer and Cane 2011:
Pitts-Singer, T.L. and J.H. Cane. 2011. The alfalfa leafcutting bee, Megachile rotundata : the worldrsquo;s most intensively managed solitary bee. Annual Review of Entomology 56: 221ndash;37.; Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).; Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). It was later found to be an important pollinator and subsequently commercialized for alfalfa seed production and has been investigated as an alternative pollinator for other crops (Pitts-Singer and Cane 2011Pitts-Singer and Cane 2011:
Pitts-Singer, T.L. and J.H. Cane. 2011. The alfalfa leafcutting bee, Megachile rotundata : the worldrsquo;s most intensively managed solitary bee. Annual Review of Entomology 56: 221ndash;37.; Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).; Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). Not all effects of this introduction are positive, however, and it may increase the incidence of chalkbrood disease (an infection by Ascosphaera aggregata) to native Megachile spp. when they co-occur in fields. Although it is widespread in the U.S., it is rarely found outside agricultural settings (Pitts-Singer and Cane 2011Pitts-Singer and Cane 2011:
Pitts-Singer, T.L. and J.H. Cane. 2011. The alfalfa leafcutting bee, Megachile rotundata : the worldrsquo;s most intensively managed solitary bee. Annual Review of Entomology 56: 221ndash;37.).

M. sculpturalis is from eastern Asia and was first found in the U.S. in 1990 (Laport and Minckley 2012Laport and Minckley 2012:
Laport, R.G. and R.L. Minckley. 2012. Occupation of active Xylocopa virginica nests by the recently invasive Megachile sculpturalis in upstate New York. Journal of the Kansas Entomological Society 85: 384ndash;386.). It is currently found in Quebec, Canada and the eastern and central U.S., where it can displace native bees (Laport and Minckley 2012Laport and Minckley 2012:
Laport, R.G. and R.L. Minckley. 2012. Occupation of active Xylocopa virginica nests by the recently invasive Megachile sculpturalis in upstate New York. Journal of the Kansas Entomological Society 85: 384ndash;386.; Droege 2015Droege 2015:
Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab ( https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf ).). It is expanding its range westward (Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.).

M. timberlakei was originally described from Hawaii in 1920, but its native range has been called into question (Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.). It has been suggested that it was actually introduced in the South Pacific, since multiple related species occur in Southeast Asia. It is a commonly found widespread species that is found on Hawai’i, Kauai, Lanai, Maui, Oahu, and Midway islands (Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.). Additionally, it has become a recent invasive in the Galápagos.

M. umbripennis is a resin bee with a widespread native distribution through Southeast Asia into the South Pacific (Krombein 1950Krombein 1950:
Krombein, K.V. 1950. The Aculeate Hymenoptera of Micronesia II, Colletidae, Halictidae, Megachilidae, and Apidae. Proceedings of the Hawaiian Entomological Society 14: 101ndash;142.; Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.). It was introduced to Hawaii sometime before 1899, possibly before European arrival. It is present on Hawai’i, Kauai, Maui, Midway, Molokai, and Oahu islands (Snelling 2003Snelling 2003:
Snelling, R.R., 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus ( Nesoprosopis ) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76 (2): 342ndash;356.). It has also recently arrived to Florida, although the extent of its establishment is not currently known.

Host associations

Species of Megachile can range from specialists to narrow generalists (Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). For example, M. davidsoni specializes on native golden eardrops (Ehrendorferia chrysantha) in California. Megachile fortis forages on Helianthus spp. sunflowers. Some species forage only on evening primrose (Oenothera spp.) or Fabaceae (Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.).

Nesting behavior

While Megachile spp. are solitary, they may sometimes nest in aggregations. Nests are built inside various preexisting holes in wood, rock crevices, inside dead or occasionally living hollow plant stalks, or using man-made objects like cavities in concrete, between bricks, inside copper tubing, or even keyholes (Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). Some are selective where they find their nesting sites. Megachile inimica nests primarily in mesquite trees (Prosopis spp.), while M. gentilis prefers nesting inside hollow twigs (Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). Most species nest aboveground, but some nest belowground (e.g., below the soil surface in sandy soils) (Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). Females harvest leaves, flower petals, and even plastic by cutting circular pieces and then use these materials to line and partition nest cells by chewing the edges and pasting them together in way that is comparable to papier-mâché (Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). Some species are more fastidious in the materials they use for nest construction. For example, M. montivaga uses Clarkia sp. flower petals, and M. subparallela prefers tick-trefoil (Desmodium sp.) (Wilson and Carril 2016Wilson and Carril 2016:
Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North Americarsquo;s Bees. Princeton University Press, Princeton and Oxford, 288 pp.). Some, such as members of subgenus Chelostomoides, are known to use sap or resin to build nests and are commonly known as resin bees (Michener 2007Michener 2007:
Michener, C.D. 2007. The Bees of the World (2nd ed.). Johns Hopkins University Press, Baltimore and London, 953 pp.). Some groups, like members in subgenus Chalicodoma, use mud, sand, or pebbles that are glued together and coated over to waterproof the cell (Michener 2007Michener 2007:
Michener, C.D. 2007. The Bees of the World (2nd ed.). Johns Hopkins University Press, Baltimore and London, 953 pp.). The habit of nesting in preexisting holes contributes to their movement by humans, since they may nest in wooden shipping pallets, inside shipping containers, or directly inside trade products.

Distribution

Megachile is a very large genus of bees with cosmopolitan distribution. It can be found throughout North America in a wide variety of habitats (Mitchell 1933Mitchell 1933:
Mitchell, T.B. 1933. A revision of the genus Megachile in the Nearctic region Part I: classification and descriptions of new species (Hymenoptera: Megachilidae). Transactions of the American Entomological Society 59: 295ndash;361.). There are more species of adventive Megachile globally than any other bee genera. Twelve species of introduced Megachile occur in the continental U.S. and Canada; six of these species have been introduced to Hawaii (Russo 2016Russo 2016:
Russo, L. 2016. Positive and negative impacts of non-native bee species around the world. Insects 7: 69.).

​Distribution map generated by Discover Life -- click on map for details, credits, and terms of use.

References

Barthell, J.F., G.W. Frankie, and R.W. Thorp. 1998. Invader effects in a community of cavity nesting megachilid bees (Hymenoptera: Megachilidae). Environmental Entomology 27:240-247.

Droege, S. 2015. The Very Handy Manual: How to Catch and Identify Bees and Manage a Collection. USGS Native Bee Inventory and Monitoring Lab. (https://www.pwrc.usgs.gov/nativebees/Handy%20Bee%20Manual/The%20Very%20Handy%20Manual%20-%202015.pdf).

Gonzalez, V.H. 2013. Taxonomic comments on Megachile subgenus Chrysosarus (Hymenoptera: Megachilidae). Journal of Melittology 5: 1–6.

Krombein, K.V. 1950. The Aculeate Hymenoptera of Micronesia II, Colletidae, Halictidae, Megachilidae, and Apidae. Proceedings of the Hawaiian Entomological Society 14:101-142.

Laport, R.G. and R.L. Minckley. 2012. Occupation of active Xylocopa virginica nests by the recently invasive Megachile sculpturalis in upstate New York. Journal of the Kansas Entomological Society 85:384-386.

Michener, C.D. 2007. The Bees of the World (2nd ed.). Johns Hopkins University Press, Baltimore and London, 953 pp.

Mitchell, T.B. 1933. A Revision of the genus Megachile in the NearcticNearctic:
biogeographical region comprising North America as far south as northern Mexico, together with Greenland
Region Part I: Classification and Descriptions of New Species (Hymenoptera: Megachilidae). Transactions of the American Entomological Society 59:295-361.

Pitts-Singer, T.L. and J.H. Cane. 2011. The alfalfa leafcutting bee, Megachile rotundata: the world’s most intensively managed solitary bee. Annual Review of Entomology 56:221-37.

Praz, C. J. 2017. Subgeneric classification and biology of the leafcutter and dauber bees (genus Megachile Latreille) of the western PalearcticPalearctic:
the largest biogeographic region; consists of Europe, Asia north of the Himalaya foothills, Northern Africa, and the northern and central parts of the Arabian Peninsula
(Hymenoptera, Apoidea, Megachilidae). Journal of Hymenoptera Research 55:1-54.

Russo, L. 2016. Positive and negative impacts of non-native bee species around the world. Insects 7: 69.

Snelling, R.R. 2003. Bees of the Hawaiian Islands, exclusive of Hylaeus (Nesoprosopis) (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society 76:342-356.

Trunz, V., L. Packer, J. Vieu, N. Arrigo, and C.J. Praz. 2016. Comprehensive phylogeny, biogeography and new classification of the diverse bee tribe Megachilini: Can we use DNA barcodes in phylogenies of large genera?. Molecular phylogenetics and evolution 103:245-259.

Wilson, J.S. and O.M. Carril. 2016. The Bees in Your Backyard: A Guide to North America’s Bees. Princeton University Press, Princeton and Oxford, 288 pp.