Megachilidae

The Megachilidae are a cosmopolitan family of (mostly) solitary bees whose pollen-carrying structure (called a scopa) is restricted to the ventral surface of the abdomen (rather than mostly or exclusively on the hind legs as in other bee families).
thumb|Leaves showing cuts by a leafcutter bee
Megachilid genera are most commonly known as mason bees and leafcutter bees, reflecting the materials from which they build their nest cells (soil or leaves, respectively); a few collect plant or animal hairs and fibers, and are called carder bees. All species feed on nectar and pollen, but a few are cleptoparasites (informally called "cuckoo bees"), feeding on pollen collected by other megachilid bees. Parasitic species do not possess scopae. Megachilid bees are among the world's most efficient pollinators because of their energetic swimming-like motion in the reproductive structures of flowers, which moves pollen, as needed for pollination. One of the reasons they are efficient pollinators is their frequency of visits to plants, but this is because they are extremely inefficient at gathering pollen; compared to all other bee families, megachilids require on average nearly 10 times as many trips to flowers to gather sufficient resources to provision a single brood cell.
North America has many native megachilid species, but alfalfa leafcutter bees (Megachile rotundata) are an imported species used for pollination. The most significant native species is Osmia lignaria (the orchard mason bee or blue orchard bee), which is sold commercially for use in orchard crop pollination, and which can be attracted to nest in wooden blocks with holes drilled in them (which are also sold commercially for this purpose).
==Lifecycle ==
===Nonparasitic species===
The lifecycle of nonparasitic Megachilidae is typically:
* Nests are divided into cells, each cell receives a supply of food (pollen or a pollen/nectar mix) and an egg; after finding a suitable spot (often near where she emerged), a female starts building a first cell, stocks it, and oviposits. 
* She builds a wall that separates the completed cell from the next one. 
* The larva hatches from the egg and consumes the food supply. After moulting a few times, it spins a cocoon and pupates. 
* It emerges from the nest as an adult. Males die shortly after mating, but females survive for another few weeks, during which they build new nests.
Variations:
* Nests are often (but not always) built in natural or artificial cavities. Some embed individual cells in a mass of clay or resin attached to a wall, rock surface, or plant stem.
* Nest cavities are often linear, for example in hollow plant stems, but not always (snail shells are used by some Osmia, and some species will readily use irregular cavities).
===Parasitic species===
Some genera of megachilids are brood parasites, so have no ventral scopa (e.g. Stelis and Coelioxys). They often parasitize related taxa. They typically enter the nest before it is sealed and lay their eggs in a cell. After hatching, the parasite larva kills the host larva, unless the female parasite has already done so, and then consumes the provisions. Parasitic species are of equal size or smaller than their victims. In 1921, the journal American Museum Novitates published a preliminary report on parasitic megachilid bees of the western United States.
==Evolution and taxonomy==
thumb|Coelioxys acanthura, female
The fossil record for megachilid bees is poor, but a Middle Eocene dicotyledonous leaf shows definite semicircular cutouts along its margin, implying that leaf-cutting bees existed at that time. Multiply-cut leaves and rare body fossils from the Eocene of Germany and the Paleocene of France suggest that Megachilinae began cutting leaves early in their evolution. Phylogenetic analysis yields an age consistent with this Eocene origin for the group.
*Subfamily Fideliinae
**Tribe Pararhophitini
***Pararhophites
**Tribe Fideliini
***Fidelia
***Neofidelia
*Subfamily Megachilinae
Main article: Megachilinae
**Tribe Lithurgini
***Lithurgus
***Microthurge
***Trichothurgus
**Tribe Osmiini
***Afroheriades
***Ashmeadiella
***Atoposmia
***Bekilia
***Chelostoma
***Haetosmia
***Heriades have narrow abdominal bands. They resemble small Osmia, but they are oligolectic (specialized on a few subfamilies of Asteraceae) and use resin from conifers, as well as plant fibers and sand, as cell wall material.
***Hofferia
***Hoplitis
***Hoplosmia
***Noteriades
***Ochreriades
***Osmia
***Othinosmia
***Protosmia
***Pseudoheriades
***Stenoheriades
***Stenosmia
***Wainia
***Xeroheriades
**Tribe Anthidiini
***Acedanthidium
***Afranthidium
***Afrostelis
***Anthidiellum
***Anthidioma
***Anthidium
***Anthodioctes
***Apianthidium
***Aspidosmia
***Austrostelis
***Aztecanthidium
***Bathanthidium
***Benanthis
***Cyphanthidium
***Dianthidium
***Duckeanthidium
***Eoanthidium
***Epanthidium
***Euaspis
***Gnathanthidium
***Hoplostelis
***Hypanthidioides
***Hypanthidium
***Icteranthidium
***Indanthidium
***Larinostelis
***Neanthidium
***Notanthidium
***Pachyanthidium
***Paranthidium
***Plesianthidium
***Pseudoanthidium
***Rhodanthidium
***Serapista
***Stelis Panzer and related genera (stelidine bees) are cleptoparasites on other Megachilidae. They belong to the tribe Anthidiini. Subgenus Heterostelis is parasitic on Trachusa.
***Trachusa
***Trachusoides
***Xenostelis
**Tribe Dioxyini
***Aglaoapis
***Allodioxys
***Dioxys is a brood parasites of Megachile, Anthidium and Osmia.
***Ensliniana
***Eudioxys
***Metadioxys
***Paradioxys
***Prodioxys
**Tribe Megachilini
***Coelioxys is a brood parasites of Megachile. Females have a pointed conic abdominal apex (tip); males have several spikes on their apex.
***Megachile
***Radoszkowskiana
**Incertae Sedis
***Neochalicodoma
***Stellenigris
==References==
==External links==
*Palaearctic Osmiine Bees
* leafcutting bees on the University of Florida / IFAS Featured Creatures Web site
* Online Guides to all the eastern North American Megachilidae
* Bugguide. Information and photos of Mechalidae of North America
Category:Megachilidae