Mason bee house: for red mason bees, not the bees in your brickwork

At a glance: red mason bees

• Flight period: March to June, among the earliest bees active in the UK.
• Tunnel size: 7–9mm, roughly 8mm being the sweet spot.
• Depth: 10–15cm for a healthy mix of male and female offspring.
• Cell seal: wet mud, carried and packed by the female.
• Not the same as: "masonry bees" reported nesting in walls — see below.

Why the red mason bee is worth attracting to fruit trees

A honeybee packs pollen wet into leg baskets, which holds it firmly in place and makes little of it available to the next flower she visits. A red mason bee carries pollen dry in a dense brush of hairs on the underside of her abdomen and belly-flops into each bloom, dislodging pollen liberally as she goes. She is also active in cooler, greyer conditions than honeybees tolerate — a fair description of most British spring days — which means she is often working an orchard while honeybee colonies are still clustered indoors. For anyone with apple, pear, plum or cherry trees, a small resident population of mason bees is disproportionately useful pollination for very little effort.

The nesting cycle, in order

1. Males emerge first, from around mid-March, and patrol tunnel entrances without nesting.
2. Females emerge a few days to a couple of weeks later and mate near the nest site.
3. Each female selects a tunnel, then makes repeated trips gathering pollen and nectar into a loaf at the tunnel's back.
4. She lays an egg on the loaf, then seals the cell with a wall of wet mud carried in her mandibles.
5. She repeats this down the tunnel — female eggs at the sheltered back, male eggs nearer the entrance — then caps the whole tunnel with a thicker mud plug.
6. The adults die off through June; the next generation develops in place, unseen, until the following March.

What a mason bee house needs to get right

Tunnels close to 8mm, 10–15cm deep

Too narrow and she cannot turn to pack pollen properly; too wide and she cannot pack the mud wall tightly enough to keep damp and mites out. Depth affects the sex ratio of the brood, as explained fully in our hole size and depth guide.

A source of workable mud

This is the one requirement unique to mason bees among common garden species. Bare, slightly damp soil within easy flying distance — a patch of unpaved bed, a shallow tray of loamy earth kept moist through spring — gives her material to build with. Gardens that are entirely paved, decked or covered in dry gravel remove this option and mason bees will not use a house nearby.

A dry, overhanging roof

Mud caps that get repeatedly soaked in driving rain soften, crack, and let damp reach the pollen loaf behind them, which then moulds. A copper or similar roof with a real overhang keeps the whole nesting face dry through a wet British spring.

Recognising red mason bee activity versus other tenants

Clearing up the "masonry bee" confusion

Red mason bees get their name from building nest cells with mud, not from nesting in masonry — they are tunnel-nesters through and through and will not excavate brick or render. What homeowners sometimes call "masonry bees" in a wall are usually solitary bees or wasps making use of gaps that already exist in old, soft or crumbling mortar, and it is a maintenance issue for the wall rather than a wildlife opportunity worth encouraging. The fix is unrelated to anything a nesting house offers: repoint failing mortar as routine upkeep, and give any bees you actually want to support a proper mud-and-timber house sited away from the building instead.

Common mistakes with mason bee houses

• Putting the house up after March and missing the emergence window for that year.
• No mud source nearby — the single most overlooked requirement for this species.
• Bringing the house indoors for winter, which triggers early emergence into a flowerless garden.
• Spraying insecticide on nearby roses or lawns, which drifts further than expected and affects foraging females.

What to look for when buying one

For mason bees specifically, prioritise 7–9mm tunnels at 10–15cm depth, a solid rear seal, and a roof that genuinely overhangs the nesting face — then check the wider range covers 2mm to 10mm so leafcutters and smaller species have a home later in the season too. Our care guide covers what to do, and not do, once bees move in.

The Wild Bee Hotel is drilled with mason-bee-sized tunnels alongside the full 2mm–10mm range, hand-sanded inside and at the rim, set into 19mm untreated Western red cedar with a solid rear panel and a hand-formed copper roof overhanging every side. £39.99, free worldwide shipping, 30-day money-back guarantee, and dispatched within 2 working days so it can be up before the March emergence.