Insect Hotels: What Actually Moves In

You know the picture: a cheerful little wooden house with a gable, stuffed with cones, bark mulch, straw and a few crossed twigs, plus a plastic ladybird for good measure. It looks like a clear conscience. Only nothing ever moves in. Most so-called insect hotels are decoration, not a nesting aid. That is not bad news but good news: once you understand what wild bees actually need, you can build something in an hour that truly hums come April. The best time to build is right now, CW 6 to 12, so everything is finished and aired out before the first mason bees fly.

Why most insect hotels stay empty

An insect hotel sells a promise it can rarely keep. The very materials that make it look full and decorative are useless to wild bees: no bee can build a brood cell between the scales of a pine cone, bark mulch rots and moulds, and perforated bricks tend to have chambers that are far too large and rough.

Then there is a craftsmanship problem. Many cheap hotels are drilled from softwood into end grain, that is, into the cut face of a branch section. There the wood tears open when drilled, leaving fibre tufts and cracks, and a wild bee with her delicate wings avoids such holes. What remains is a pretty object that soothes your conscience and gives the animals nothing.

Who actually moves in?

The word insect hotel is misleading. It sounds as if every insect turns up, yet in truth only a few groups use such nesting aids, above all cavity-nesting wild bees. The most rewarding first tenant is the red mason bee, Osmia bicornis, a gentle, plump bee that flies as early as March and prefers holes of 6 to 8 mm. Alongside her come the horned mason bee, resin bees, yellow-faced bees, small scissor bees and a few solitary wasps. All of them live solitary lives; there is no colony, no queen, no defensive swarm.

Keep your expectations realistic: the great majority of the roughly 600 wild bee species in Germany do not nest in tubes at all, about three quarters dig their brood tunnels into the ground. For those you build no hotel but create open, sunny soil or a sand bed. So if only a few tubes in the hotel get occupied, that is no failure but exactly what to expect.

Food first: no flowers, no tenants

The finest nesting aid stays empty if nothing blooms nearby. Wild bees rarely fly far, many only 100 to 300 metres. Provide a continuous succession of bloom from March to September: early willows and crocus, then fruit trees, comfrey and viper's bugloss, later bellflowers, wild aster and ivy. Single, open flowers are a must; double cultivars deliver almost no pollen.

Viper's bugloss is one of the very best wild-bee pastures there is: it keeps supplying nectar and pollen for weeks and shrugs off midday heat on poor soils. Combine it with borage and crocus and you cover spring right through to late summer. You are not building a hotel, you are building a small habitat.

The right drilling, step by step

This is where everything is decided. At its core a good nesting aid is nothing more than a block of well-seasoned hardwood with clean drill holes. Take beech, oak, ash or fruitwood, thoroughly dried so no cracks open up later. Softwood like spruce or pine will not do, it splinters.

1. Drill into the long side of the wood, across the grain, never into end grain. End grain, the cut face with the annual rings, tears open and moulds more easily.

2. Choose diameters from 2 to 9 mm, with the emphasis on 3 to 6 mm. These sizes are the most sought after. Drill a range of diameters and you appeal to several species.

3. Drill 8 to 10 cm deep, but not all the way through. A closed end is essential, because the bees need a back wall. Leave about 1 to 2 cm between the holes.

4. Deburr every hole: pull the bit out cleanly several times and smooth the rim with fine sandpaper or a small round file. Not a single splinter may remain, and blow out the drilling dust at the end.

Material that works, and material that harms

Besides drilled hardwood, only two further materials really get used: hollow stems and pithy stalks. Both must be cleanly prepared.

Location and orientation

Even a perfect nesting aid stays empty if it hangs in the wrong place. Wild bees love warmth and like it dry.

• Sun: entrance facing southeast to south, so the morning sun warms the tubes early. Full shade is avoided.
• Dry: a small roof or overhang keeps the rain off. Wet tubes mould and the brood dies.
• Firm: the nesting aid must not sway in the wind. Screw or brace it solidly, at least half a metre above the ground.
• Clear: the entrance must be open, no twigs right in front of it. Give the bees a free flight path.

What you can happily leave out

The big, multi-storey hardware-store hotels are above all one thing: expensive and decorative. A single well-drilled hardwood block, plus a tight bundle of reed, occupied and used, is worth more than a man-high insect hotel full of filler.

Care and a look at the second year

The effort is small. Sealed tubes, usually capped with a plug of clay, mean success: behind them the brood develops through summer, autumn and winter. Do not open them, do not poke inside. The finished bees emerge on their own the following spring.

Leave the nesting aid hanging all year round, through winter too, a dry and sheltered spot is enough. Only when tubes go brittle or mouldy after two or three years do you replace the stems or drill the wooden block anew. A common mistake is too much care: cleaning out tubes in autumn or bringing the nesting aid indoors only upsets the natural rhythm.

And if you want to do more for wild bees, think beyond the box. Which flowers carry them from March to October is covered in the article on nesting aids and forage plants. For the ground-nesting majority you build a sand bed, an open, sunny patch of sand. Together with a flower-rich pasture, the single nesting aid becomes a real habitat.

Häufige Fragen

Why is nothing moving into my insect hotel?

Usually it comes down to material and drilling: cones, straw and bark mulch never get occupied, only drilled hardwood, clean reed or bamboo stems and pithy stalks. If the holes are frayed, drilled into end grain or rough, the bees avoid them. The second common reason is a lack of food: without flowering forage plants within 100 to 300 metres, no one flies in. The third is location: sunny facing southeast, dry and firmly mounted solves most cases.

Which drill diameters are right for wild bees?

Drill holes between 2 and 9 mm, with the emphasis on 3 to 6 mm, as those are the most sought-after sizes. The red mason bee likes 6 to 8 mm, many smaller species considerably less. Mix several diameters and you appeal to different species. Besides the diameter, what matters is a depth of 8 to 10 cm with a closed end and a smooth rim.

Where and how high should I hang a nesting aid?

Sunny, with the entrance facing southeast to south so the morning sun warms the tubes early. At least half a metre above the ground, higher is fine, and above all firm so nothing sways in the wind. A small roof keeps the rain off, because damp lets the brood go mouldy. The entrance should be clear, with no twigs right in front of it.

When is the best time to build and hang the insect hotel?

The best time to build is late winter, roughly CW 6 to 12. By then the nesting aid is finished and aired out before the first mason bees fly from March. Freshly drilled wood should dry through beforehand, so it is better to be ready a few weeks early. Leave it untreated, no lacquer, no oil.

Are wild bees in an insect hotel dangerous for children and pets?

No. The tenants are solitary wild bees like the red mason bee; they form no colony and defend no nest. Their sting is too weak to pierce human skin, and they practically never sting. You can hang the nesting aid without worry within sight of a seating area. For children, watching the bees fly in and out is even a lovely encounter with nature.