Solitary and Mason Bees

While the social colonies of honey bees and bumblebees often capture the most attention, Scotland is also home to a diverse and fascinating group of wild pollinators known as solitary bees. These industrious insects do not live in hives or serve a queen; instead, each female works alone to construct her own nest and provide for her young.

Scotland’s varied landscape supports a significant portion of the UK’s bee biodiversity:

• Total Solitary Species: There are approximately 79 species of solitary bees recorded in Scotland.
• Mason Bees: Within this group, mason bees are a specific type from the family Megachilidae. Around 14 species from this broader family have been recorded in Scotland, representing several different genera.
• Specialist Residents: Scotland is home to unique varieties like the Mountain Mason Bee (Osmia inermis) and the Pinewood Mason Bee (Osmia uncinata), which in the UK are found exclusively in the Scottish Highlands.

The term “mason bee” refers to their professional-level building skills. These bees often use mud or other masonry-like materials to seal their nests in cavities, such as hollow stems, holes in wood, or even the mortar of old stone walls – a habit that often earns them the name “masonry bees”.

Solitary bees are remarkably peaceful and are widely considered some of nature’s most efficient pollinators. For instance, a single Red Mason Bee is estimated to provide as much pollination as 120 worker honey bees. Despite their independent nature, many species are happy to nest near one another, making them common and welcome visitors to “bee hotels” in gardens across the country.

What makes Solitary and Mason Bees different?

Solitary bees, including the specialized mason bees, operate on a fundamentally different social and biological blueprint compared to their colonial relatives and the predatory wasp.

The most defining characteristic of solitary bees is their lack of a social hierarchy.

• Single-Handed Effort: Unlike honey bees or bumblebees, there is no queen and no worker class. Each female is fertile and responsible for building her own nest, foraging for food, and laying her own eggs.
• No Central Home: While they may nest in close proximity to one another (known as “aggregations”), they do not share resources or assist each other with rearing young.

While wasps use paper and honey bees use wax, solitary bees are the “recyclers” and “masons” of the insect world:

• Mineral and Plant Materials: Mason bees are named for their habit of using mud or clay to partition their nesting chambers. Other solitary species, such as leafcutter bees, use precisely cut circular pieces of leaves or flower petals to line their nests.
• Diverse Locations: While social bees often require large cavities (like hives or burrows), solitary bees utilize tiny gaps, such as hollow plant stems, beetle holes in dead wood, or even the crumbly mortar of stone walls.

Solitary bees are often more efficient pollinators than honey bees or wasps due to their “messy” foraging style:

• Dry Pollen Transport: Instead of wetting pollen to pack it into neat “baskets” (corbicula) like honey bees and bumblebees, many solitary bees carry dry pollen on a brush of hairs on their abdomen called a scopa.
• Increased Transfer: Because the pollen is carried loosely and dry, it is much more likely to fall off and fertilize the next flower the bee visits.

Because solitary bees have no large colony or honey stores to defend, they are incredibly docile.

• Low Aggression: They generally only sting if they are handled roughly or trodden upon.
• Mild Sting: In many solitary species, the stinger is too small or weak to penetrate human skin, making them the safest bees to encourage into family gardens.

Feature	Solitary / Mason Bee	Honey Bee	Wasp
Social Structure	Independent (Solitary)	Highly Social (Colony)	Social or Solitary
Pollen Transport	Dry hairs on legs/abdomen	Damp pollen baskets	None (Carry meat)
Nest Architecture	Mud, leaves, or tunnels	Secreted wax combs	Paper wood-pulp
Diet	Pollen and Nectar	Pollen and Nectar	Nectar and Insects

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