Osmia (Helicosmia)


Family: Megachilidae
Subfamily: Megachilinae
Tribe: Osmiini
Genus: Osmia Panzer, 1806
Subgenus: Helicosmia Thomson, 1872
Common name: none


Osmia (Helicosmia) are metallic blue or green bees (although occasionally not metallic or only faintly so) with pale hairs on their head, thorax, and abdomen. They can have black or white scopal hairs and typically possess pale apical fasciae on their terga (Michener 2007). They range in body length from 7.5–15 mm (Michener 2007).

Diagnostic characteristics

(modified from Michener 2007)

  • Propodeum surface is dull.
  • Hind coxa without strong longitudinal carina along inner ventral angle.
  • Female clypeal margin usually with orange hairs beneath the rim of the clypeus arranged into four tufts. In rare cases, they may be absent or not distributed into tufts.
  • Female mandible robust, with depression across base that is abruptly set off from adjacent mandibular surface.
  • Male S2 large and apically convex.
  • Male S3 medially emarginate, emargination largely hidden by enlarged S2.
  • Male S4 apical margin has two carinae laterally with a narrow, hairless, shiny groove between them.
  • Male S6 lacks longitudinal groove and lacks a projecting lobe.
  • Male T7 has a small midapical emargination or is bidentate.

May be confused with

Osmia (Helicosmia) may be confused with O. (Diceratosmia) and O. (Pyrosmia) due to similar grooved margins of S4 in males and the presence of apical tergal fasciae of plumose hairs (Michener 2007). However, O. (Helicosmia) can be differentiated from the two other subgenera due to the characteristics listed above.

Host associations

Osmia (Helicosmia) have been observed visiting Fabaceae, Boraginaceae, Lamiaceae, Antirrhineae, Asteraceae, Hypericaceae, Brassicaceae, Ranunculaceae, Carduoideae, Cistaceae, Polygalaceae, and Antirrhineae (Banaszak and Romasenko 1998; Grace 2010; Müller 2018).

Nesting behavior

Osmia (Helicosmia) nests predominantly in preexisting cavities such as holes in wood, stems, and abandoned insect burrows (Michener 2007; Müller 2018). Cell partitions and nest plugs are made of masticated leaf materials and sometimes chewed flower petals (Müller 2018).

Osmia (Helicosmia) melanogaster have been observed nesting in abandoned snail shells, in fissures in stone walls, insect burrows in dead wood, and hollow stems (Banaszak and Romasenko 2001; Michener 2007; Müller 2018).

Osmia dimidiata nest in hollow stems and abandoned cells in nests of other bees. Nests are linear, and generally contain 1–2 cells, but can have as many as 9 brood cells (Ivanov et al. 2013).

Osmia (Helicosmia) heteracantha nest in insect burrows in the ground and in abandoned cells from exposed Hoplitis nests (Müller 2018).

Osmia orientalis nest in snail shells, with up to 10 cells per shell. Cell partitions are constructed of masticated leaves and are not fully closed except for the outer partition. The last cell partition is thick, complete, and acts as the nest plug (Maeta 1978; Kandori et al. 2010; Müller 2018).

Osmia aurulenta also nest in snail shells, with up to 17 cells arranged side by side with leaf pulp. The shell surface is covered with leaf pulp and left alone (no turning or moving) after the nest is closed (Westrich 1989; Müller et al. 1997; Banaszak and Romasenko 2001; Müller 2018).

Osmia fasciata nests in abandoned burrows and brood cells of an Amegilla bee species that nests in steep, hard-packed, sandy slopes. Cells are arranged linearly and are built from chewed leaves (Müller 2018).


Osmia (Helicosmia) consists of 72 described species with at least 1 undescribed species (Müller 2018). There are 5 known species that occur in North America.

Known invasives

Osmia caerulescens is native to Europe, the Middle East, Asia, and North Africa. They were introduced to North America from Europe in the 1800s and now occurs throughout the eastern half of the U.S. (Michener 2007; Russo 2016).


Osmia (Helicosmia) occur throughout North America to Mexico, and throughout Europe, northern Africa, the Mediterranean Basin, and Asia (Michener 2007; Müller 2018).

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

<p><em>Osmia coloradensis</em> female face, photo: Chelsey Ritner</p>
Osmia coloradensis female face, photo: Chelsey Ritner
<p><em>Osmia coloradensis </em>female lateral habitus, photo: Chelsey Ritner</p>
Osmia coloradensis female lateral habitus, photo: Chelsey Ritner
<p><em>Osmia coloradensis </em>female abdomen, photo: Chelsey Ritner</p>
Osmia coloradensis female abdomen, photo: Chelsey Ritner