Orange-vented Mason Bee - Osmia leaiana


The males of both O. leaiana and O. caerulescens are extremely hard to distinguish, being about 6mm long, shining metallic green and having bright ginger hairs when fresh. The best character is microscopic: look at the downward-sloping front surface of the first gastral tergite. It is shining in O. caerulescens and matt with reticulation in O. leaiana. This means that set specimens need to be arranged in order to see this feature. The females are quite different; both are about 10mm long, but O. caerulescens is generally smaller, dark blue with a black scopa under the abdomen and O. leaiana is generally larger, dark brown, with a bright orange scopa under the abdomen.

Identification difficulty

It uses a wide range of habitats, especially sites with plentiful thistles and knapweeds. It can be frequent in gardens and is one of the species that like to exploit bee hotels.

When to see it

Between May and August.

Life History

Nests in cavities in dead wood, walls or cliffs. Adults collect pollen exclusively from Asteraceae.

UK Status

Restricted to England and Wales. It is less frequently found than O. caerulescens, but occurs in similar habitats.

VC55 Status

Status in Leicestershire and Rutland not known.

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Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map