Table of contents
Introduction
The Blue Mason Bee (Osmia caerulescens) is a small, fast-moving solitary bee named for the subtle blue sheen often visible on its dark body. Active from spring into early summer, it is a familiar species in gardens and allotments where suitable flowers and nesting sites are available.
In the UK, this bee is commonly seen around hedgerows, gardens, parks, and open countryside. Despite its modest size, it is an effective pollinator of a wide range of plants and plays a valuable role in early- to mid-season pollination.
Although generally common, the Blue Mason Bee can be affected by habitat loss, pesticide use, and a lack of nesting opportunities. In this guide, you’ll learn how to identify Osmia caerulescens, tell it apart from similar mason bees, and understand how simple garden actions can support it.
Identification & Key Facts
| Attribute | Details |
|---|---|
| Common Name | Blue Mason Bee |
| Latin Name | Osmia caerulescens |
| Size | ~8–11 mm |
| Location | Widespread across the UK |
| Active Months | April to July |
| Habitat | Gardens, hedgerows, parks, open countryside |
| Nesting Behaviour | Cavity nester in holes, stems, walls |
| Social Behaviour | Solitary |
| Flora | Bramble, buttercup, fruit blossom, wildflowers |
| UK Status | Common |
How to Identify the Blue Mason Bee
The Blue Mason Bee is a small, dark bee with a metallic blue-black sheen that can be visible in good light. It has a compact body shape and a quick, darting flight, often seen close to flowers or nesting sites.
In the UK, it is frequently spotted in gardens and hedgerows, especially where bramble, buttercups, and fruit trees are flowering. Like other mason bees, females carry pollen on the underside of the abdomen rather than on the hind legs.
Physical Characteristics
- Female – Slightly larger, with a robust body and visible pollen-carrying hairs on the underside of the abdomen.
- Male (Drone) – Smaller and slimmer, often with longer antennae and lighter facial hair.
Similar Species
The Blue Mason Bee can be confused with other small cavity-nesting bees:
- Orange-vented Mason Bee (Osmia leaiana) – Has a noticeable orange underside to the abdomen.
- Red Mason Bee (Osmia bicornis) – Larger and more obviously reddish-brown.
- Small Carpenter Bee (Ceratina cyanea) – More slender with a shinier, less hairy appearance.
If you’re unsure which bee you’ve spotted, our Bee Identification guide can help you narrow down UK species by size, colour, and behaviour.
Why the Blue Mason Bee Matters
The Blue Mason Bee is an efficient pollinator of many garden plants, wildflowers, and fruit trees. Its activity helps support early and mid-season flowering plants, contributing to both food production and biodiversity.
Because it readily nests in small cavities, it adapts well to gardens and urban spaces, making it an important pollinator close to where people live.
FAQs
No. It is a calm species and very unlikely to sting unless handled.
It is mainly active from spring into early summer, typically April to July.
No. It is considered common and widespread.
Females can sting, but stings are rare and usually only occur if the bee is trapped.
How You Can Help
Supporting the Blue Mason Bee is simple and garden-friendly:
🌿 Plant Bee-Friendly Flowers
- Bramble, buttercup, fruit blossom, native wildflowers
🚫 Avoid Harmful Pesticides
- Avoid insecticides that contaminate nectar and pollen
🏡 Provide Nesting Spaces
- Leave hollow stems, old walls, or provide bee hotels with small tubes
By offering flowers and nesting spaces, you help support the Blue Mason Bee and other cavity-nesting pollinators.
