Osmia bicornis (Red mason bee)♀︎♂︎

Last update: 2 May 2020


SPECIES: Red mason bee (Osmia bicornis)
GENUS OSMIA (Mason bees)




The Red mason bee (Osmia bicornis, synonym Osmia Rufa) is a yearly returning visitor of the garden and with that a permanent resident.

Red mason bee ♀︎ (Osmia rufa / Osmia bicornis) on Meadow buttercup (Ranunculus acris)
Red mason bee ♂︎ investigates a nesthole looking for a female
(Osmia rufa / Osmia bicornis)


The bee is common in the Netherlands [1,2].



The species is on of the first bees to awake around spring in March and emerges immediately on the bee hotel. The total number increases steadily until a large number of them is buzzing around the bee hotel. In July it will disappear again.

The bee will inspect any hole that seems slightly interesting as a potential nesting place, but is not interested in bamboo sticks that stand vertically in the ground as plant supports. Other bees and wasps will use those too.


The name mason bee refers to the behaviour in which the bee makes a wall at the backside of the nesting site and between the brood cells, and finally will also close the entrance to the nest using mud. The publication  ‘Gasten van bijenhotels’ [3] provides nice visual examples of this.

As indicated does the species use nesting help like bee hotels. Together with the Ridge-Saddled Carpenter Bee the species is a bulk consumer of the bee hotel nesting space.

Red mason bee (Osmia bicornis / syn. Osmia rufa), closed nest entrance with walled in plant material


This species has been seen on [3]:

  • Lungwort (Pulmonaria officinalis)
  • White nettle (Lamium album)
  • Ground-ivy (Glechoma hederacea)
  • White clover (Trifolium repens)
  • Sycamore (Acer pseudoplatanus)
  • Willow (Salix)
  • Common oak (Quernus robur)
  • Buttercup (Ranunculaceae)
  • Blackberry (Rubus fructicosus)

In the garden the species has been seen on:

  • Meadow buttercup (Ranunculus acris)
  • Common dandelion (Taraxacum officinale)
  • Rodondendron
  • Ribes


The following Red mason bee brood parasites  have been observed in the garden:

Cacoxenus indagator [4, 5]
Anthrax anthrax [3,4]
Ephialtes manifestator [1,5]
Ruby-tailed wasp (Chrysis ignita) [4]


The bee has a length of 8-12 mm [1,2].

The color of the bee can change during its life as a result of the wearing and losing of hairs which makes it more difficult to recognize it [2]. With males this happens sooner that with females.

The species is recognizeable by the following characteristics [1,2].


  1. Dark colored body with blue metal shine on head and bronze colored abdomen.
  2. Head and tergites (topside of abdomen segment) IV – VI black haired.
  3. Thorax brown-grey haired.
  4. Tergites I – III red-brown haired.
  5. Scopa (hairs on underside abdomen, used to transport pollen) red (red-orange).
  6. Clypeus (lower half face between eyes and mouth) has bend horns on each side and in the middle a two pointed lobe.
Red mason bee ♀︎
(Osmia rufa / Osmia bicornis)
Horns on sides clypeus female
Horns on sides clypeus female
Horns on sides clypeus female
Enlargement face female


  1. Blue-green shine and red-brown haired.
  2. Face and underside thorax white-yellow haired.
  3. Stern and tergites IV – VII black haired.
Red mason bee ♂︎
(Osmia rufa / Osmia bicornis)


1 Peeters, T.M.J., H. Nieuwenhuijsen, J. Smit, F. van der Meer, I.P. Raemakers, W.R.B. Heitmans, C. van Achterberg, M. Kwak, A.J. Loonstra, J. de Rond, M. Roos & M. Reemer 2012. De Nederlands bijen (Hymennoptera: Apidae s.l.). - Natuur van Nederland 11, Naturalis Biodiversity Center & European Invertebrate Survey - Nederland, Leiden.

2 wildebijen.nl, "De Nederlandse bijen en hun relaties, overzicht van in Nederland en Vlaanderen voorkomende solitaire en sociale bijen (Apidea s.l.)"

3 Breugel, P. van 2014. Gasten van bijenhotels. – EIS Kenniscentrum Insecten en andere ongewervelden & Naturalis Biodiversity Center, Leiden.

4 KRUNIC, M & Stanisavljević, Ljubiša & PINZAUTI, M. (2005). The accompanying fauna of Osmia cornuta and Osmia rufa and effective measures of protection. Bull. Insectol. 58. 141-152., pag: 145

5 MACIVOR, Scott. Adult emergence order in a community of cavity-nesting bees and wasps, and their parasites. bioRxiv, 2019, 556456.

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