Osmia bicolor (fleam dyke)

Probably the bee highlight of the year

The males of this species are among the first of the solitary bees to appear in the spring, with one exceptional record as early as late February. They are shortly followed by the distinctive females.

Status (in Britain only)
Classified as a Nationally Notable (Nb) species by Falk (1991).
Generally calcareous grassland and open deciduous woodland on chalk and limestone soils.
Flight period
Univoltine; April to early July. The males are very short-lived in comparison with the females.
Nesting biology
Females establish their nests in empty snail shells, including those of Helix pomatia, Cepaea nemoralis, C. hortensis and Monacha cantiana. Nests contain about four or five cells, depending on the size of shell used. Cell partitions and the closing plug consist of leaf mastic (i.e. masticated portions of green leaf). The space between the last cell partition and the closing plug is filled with a rubble containing very small snail shells and pieces of chalk, or soil. When the nest is completed the female covers the shell with a mound of dead grass stems, beech scales or leaf fragments (Perkins, 1884, 1891; G R Else, pers. obs.). The reason for this behaviour is not known, but it may camouflage the nest from possible parasites and predators at a time when it may be vulnerable to such attack….BWARS

6 thoughts on “Osmia bicolor (fleam dyke)

    • Thanks , I see your in Aberdeen, far less bees in the north I live in Balfron Stirlingshire for years by loch lomond, I have found a couple of rare bees in scotland the Northern colletes bee and the great yellow bumblebee .. but when you see the amount of species of bes down south compared to the north it is such a difference , obviously due to weather and forage…. I see you say about the decline of bees the problem is that with all the cuts over the years the entomologists that used to record bees and wasps etc have gone and its only now the government etc have realised and are starting training programmes up and most work is done by citizen scientists .. check out BWARS

  1. I can’t think of anything more exciting than watching an Osmia bicolour come out of her shell. I still have not seen one. Not that I’m jealous…Amelia

    • I was like an excited child , I left the house way to early it was still cold and cloudy but I stuck it out for 3 hours and saw over 13 females and many males .. saw about 3 using shells wish I had got better photos but they move so quickly

    • I can’t think of anything more exciting than watching an Osmia bicolour come out of her shell. I still have not seen one. Not that I’m jealous… I’m just thinking, if I did see a female at the moment I would probably think it was an Osmia cornuta as they are very common here. How could I tell without catching one? Amelia

  2. the first thing I would suggest is find out if they are in your area , I had not looked for them here as most of cambridge is reclaimed fen so dark peaty soils or sandy , but just to the south is chalky soils which is a requirement for these bees .. so is there a French equivalent to BWARS as they may have a distribution map for France

Comments are closed.