How do I build a bug hotel insects will actually use?

A bug hotel is one of the few garden wildlife interventions where the details decide everything. Get the hole diameter, depth and orientation right and it fills within a season; get them wrong and it stays empty for years while looking charming. It is also the one intervention that can do harm if it is never maintained.

What you'll need

• Untreated hardwood block, or bamboo canes, or paper tubes
• A drill with sharp bits, 2 to 10mm
• A weatherproof roof or overhang
• A firm fixing at least a metre off the ground
• Fine wire mesh against birds (optional)

Step by step

1. Decide which insects you are aiming at.Solitary bees such as red mason and leafcutter bees are the main users of tubes, and they are excellent pollinators. Lacewings, ladybirds and beetles want quite different habitat — hollow stems, dense dry material, log piles and leaf litter.
2. Get the hole diameter right.Between 2 and 10mm, with the bulk of them around 6 to 8mm, which is what red mason bees prefer. A range of sizes suits a range of species. Anything much over 10mm is used by very little.
3. Get the depth right.At least 100mm, ideally 150mm, and closed at the back. Bees lay female eggs at the back and male eggs at the front, so a shallow tube produces males only. This is the single most common fault in bought hotels.
4. Make sure tubes are closed at one end.A tube open at both ends is a draughty corridor and is not used. Bamboo cut just behind a node is closed naturally; drilled blocks are closed by not drilling through.
5. Make the entrances smooth.Splinters and rough edges damage bees' wings and deter them. Drill with a sharp bit, into seasoned wood rather than green, and sand or turn the entrance clean.
6. Use the right materials.Untreated seasoned hardwood, bamboo canes, hollow dry stems such as reed or teasel, or purpose-made paper tubes. Avoid treated timber, plastic tubes, glass and anything that traps condensation.
7. Site it south or south-east facing.Morning sun warms it and gets the bees flying early. A north-facing hotel is used far less.
8. Fix it firmly, at least a metre up.It must not swing or rattle in the wind. A wobbling hotel is not used. Screw it to a wall, a post or a fence.
9. Keep it dry.An overhanging roof, or a position under an eave. Rain into the tubes rots the contents and kills the larvae. Slope the whole thing very slightly downward at the front so any water runs out.
10. Put flowers and mud nearby.Mason bees need damp bare mud or clay to seal their cells, and leafcutter bees need soft leaves such as roses and lilac. A hotel in a garden with no forage and no bare ground stays empty regardless of construction.
11. Leave some bare ground.The large majority of solitary bees nest in the ground rather than in tubes. A sunny patch of bare, undisturbed, well-drained soil or a south-facing bank does more for solitary bees than any box.
12. Clean or replace it — this matters.Tubes accumulate parasitic mites, wasps and fungal disease over a few years, and an unmaintained hotel concentrates them. Use removable paper liners or split bamboo you can open, harvest and clean the cocoons in autumn, store them somewhere cold and dry and unheated, and put them back in spring. If that is more than you want to do, replace the tube block every two years.
13. Build the other habitats too.A log pile in shade for beetles and fungi, a pile of dead stems left standing over winter for overwintering insects, leaf litter left in a corner, and a patch of long grass. Together these support far more species than any hotel.

Tips

• Bought hotels with pine cones, wood wool and big open compartments are mostly decorative. The tube section is the part that works.
• A bundle of bamboo canes cut just behind a node, tied tightly and wedged in a plastic pipe under an eave, outperforms most bought hotels and costs nothing.
• Sealed tubes in early summer means it is working — those are mason bee cells with an egg and a pollen store inside each one.

Common mistakes

• Tubes open at both ends — Bees will not nest in a through-draught. Every tube needs a closed back.
• Shallow tubes — Under about 100mm the bee produces only male offspring, which does the population little good. Depth matters as much as diameter.
• Never cleaning it — Parasitic mites and fungal disease build up over a few years, and the hotel then does more harm than good. Clean it, or replace the tubes every couple of years.
• Siting it in shade or somewhere it swings — Cold, damp and movement all put bees off. South or south-east facing, firmly fixed, and dry.
• Building a hotel in a garden with no flowers or bare ground — Nesting sites are rarely the limiting factor. Forage and bare soil usually are.

If it doesn't work

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