Solitary bee house: the tunnel spec that decides whether it works

At a glance: the four specifications that decide success

• Diameter range — not one size; 2mm to 10mm across separate tiers.
• Depth — 10–15cm; shallower tunnels produce mostly male offspring.
• Sealed rear — a solid back stops parasites reaching brood from behind.
• Roof overhang — enough projection to keep driving rain off the tunnel face.

Why "looks like a bee house" and "works like a bee house" are different things

A tidy grid of holes in a block of wood photographs well, which is exactly why so many are sold that way. But a female solitary bee is choosing a tunnel by touch and smell, not by appearance, and she will reject anything that doesn't meet her needs regardless of how the house looks on a fence post. See our species-by-species guide for which bees are actually being catered for by a given diameter.

Diameter: why one size fails almost everyone

Cheap houses are commonly drilled entirely at 6mm, because it is a single, fast setting on a production line. That fits some leafcutters reasonably well and almost nothing else. Red mason bees, the most likely tenant in a British garden, want 7–9mm and often cannot enter or exit a 6mm hole comfortably; the smallest masked bees need 2–4mm and are excluded from every mainstream house on the market. A house that actually works offers the range, not a guess.

Depth: the specification almost nobody checks

Depth is rarely mentioned on packaging, yet it changes the sex ratio of the brood a tunnel produces. Females lay daughters at the sheltered back of a tunnel and sons near the entrance, so a shallow 4–5cm tunnel — common in decorative houses built from short offcuts — produces overwhelmingly male offspring and does very little for next year's population. Aim for 10–15cm, detailed further in our hole size and depth guide.

Why cheap houses fail: a specification comparison

The seal, the roof, and the two failures they prevent

A through-drilled tunnel is not a nest, it is a corridor open at both ends, and parasitic wasps exploit exactly that gap to reach larvae from behind. A flat or barely-projecting roof lets driving rain run straight down the entrance face, soaking mud caps and growing mould on stored pollen. Both faults are invisible on a shop shelf and both are common causes of the failures covered in our troubleshooting guide.

Common mistakes buyers make

• Choosing on appearance or price alone, without checking tunnel depth or diameter range.
• Assuming bundled bamboo needs no backing panel — most does, and comes without one.
• Buying a treated or varnished house, which smells wrong to inspecting females.
• Hanging a good house in the wrong place, undoing sound construction — see positioning advice.

What to look for when buying one

Check for a genuine diameter range rather than one repeated size, tunnels at least 10cm deep, a solid backing panel, a roof that visibly overhangs the entrances, and timber thick enough to buffer temperature swings. If a listing doesn't mention depth or backing at all, assume neither has been considered.

The Wild Bee Hotel is built to that specification throughout: tiers from 2mm to 10mm, hand-sanded inside and at the rim, 10–15cm deep, a solid rear panel, 19mm untreated Western red cedar walls and a hand-formed copper roof that overhangs the face on every side. £39.99 for one, with free worldwide shipping and a 30-day money-back guarantee.