Osmia Bicolor (Male) Fleam Dyke

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Distributed predominantly in southern England and south Wales, the range being closely correlated with chalk and limestone soils. This is a predominantly central European species, becoming rare and sporadic north of Belgium. The Palaearctic range extends from southern Finland (one record only (Elfving, 1968)) to Spain, and east to the former Yugoslavia and Romania. Stoeckhert (1933) records the species from central Asia and reports that both there and in southern Europe it is largely restricted to montane sites.
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. Nests are illustrated by Geiser (1988) and Westrich (1989). Males have been found sheltering in empty snail shells during periods of inclement weather (G R Else, pers. obs.).
Flowers visited
Wood anemone (Anemone nemorosa), bluebell (Hyacinthoides non-scripta), heath dog-violet (Viola canina), bird’s-foot-trefoil (Lotus corniculatus), horseshoe vetch (Hippocrepis comosa), sainfoin (Onobrychis viciifolia), sallow (Salix spp.), ground-ivy (Glechoma hederacea), daisy (Bellis perennis) and dandelion (Taraxacum sp.)….BWARS

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