Creating homes for solitary bees

About 250 of our 280 or so species of wild bee in the UK are solitary bees which nest by themselves and not in colonies like Bumblebee and Honey bees.

About 70% of solitary bees live underground in burrows which they excavate themselves. The other 30% are cavity nesters which nest above the ground in standing dead wood, timber structures and cliff faces and steep sided banks.

In urban areas cavity nesting species often nest in old garden furniture using cavities where screws are missing, hollow metal railings on fences, rotary washing lines, gaps beneath windowsills and air bricks on the side of houses designed for ventilation. Some will excavate a nest chamber in the decaying mortar of old brick work. Historically many would have used old fashioned cob walls.

Ground nesting bees often nest in scruffy lawns, base of hedges and shrubbery and bare sunny ground. Often in sandy soils. In urban areas they will also nest in the sand between paving slabs.

In the modern built up environment cavities in buildings are becoming scarcer and we can help cavity nesting species by erecting bee hotels on south and southeast facing walls and fences creating opportunities for them to nest.

We can also cater for ground nesting bees by building nesting mounds or nesting planters.

The best homes are often natural features such as decaying trees and standing deadwood but in urban settings such things are often removed on health and safety grounds.

The images to the right show holes drilled into wooden fence posts with bees nesting in them.

Many shop bought bee hotels or ones offered by online retailers are badly designed and dreadful homes for bees. The cavities are too short or the wrong diameter and they are often treated with harmful chemicals, paints and glues. 

You should also avoid plastic, metal and any non-porous materials as this can cause moisture to become trapped encouraging moulds and fungal growth which can consume the bee larva and stores of pollen.

The simplest bee hotel is a block of wood or log disk. For log disks use wood that is greater than 15cm thick, and for blocks of wood use very thick fencing posts or timber sleepers sunk into the ground to create a monolith. You can also use large branches and tree trunks. 

Simply drill cavities into the wood using a drill. Ideally your cavities should range from 2mm diameter to 10mm diameter and be 15cm deep. Standard wood drill bits are rarely over 8cm long so you may need to buy special auger drill bits which are much longer.

You want nice clean smooth finishes to your drilled holes. Rough raggedy edges can shred bees wings. To get a smooth finish you need sharp drill bits and dry wood.

Cavities 2-3mm wide will attract Chemostoma campanularum and Yellow faced Bees such as Hylaeus communis.

Slightly larger cavities 3-4mm wide will accommodate Heriades bees which plug their nests with plant resin and a pebble dash finish of sand particles.

4-6mm will accommodate smaller mason bee species like Osmia Caerulescens and Osmia leaiana.

Cavities 6-8mm wide are great for Red Mason bee Osmia bicornis

If you create a smaller number of cavities with a diameter of 8-10mm you may attract larger leafcutters like Megachile ligneseca, Meghachile willughbelia and Anthidium manicatum. 

On continental Europe its important to avoid larger cavities as these can accommodate the invasive non native Giant Resin Bee  Megachile sculpturalis which is a threat to our native European Bees. 

The majority of your cavities should be smaller holes to accommodate the smaller bees which are often very numerous but bee hotels seldom cater for them.

The image to the right is a bee hotel I made from a wooden Wine box. I used Elder, Bamboo, Reed stems and holes in blocks of wood as nest cavities. In its first summer it attracted 14 species to nest with 100% occupancy!

Cob is a material that's been used since ancient times to clad homes made from wattle and daub.

Its an ideal material for species of bees and wasps that like to nest in vertical or steep surfaces and is a good substitute for natural soft rock and earthen cliffs.

To make cob mix equal parts garden clay, sharp sand and chopped straw together in a bucket until its a thick sticky consistency.

Stuff and compact into a mould to make a brick which you can then make a small wall from or stuff into boxes or crates. Allow to dry then stand in a sunny south facing position and wait to see if any bees move in. 

At apicultural we've made large cob nesting boxes using old fish mongers polystyrene crates. We first paint the crates in masonry paint and then clad in a mix of weak cement powder and sharp sand. This hardens the polystyrene material and UV stabilizes it so it wont break down into microplastics. We then fill them with the cob.

We have had success attracting Hairy Footed Flower Bees to nest in these boxes.