How to make a Solitary Bee Box

We noticed a solitary bee using a gap between some tongue and groove wood cladding on the rabbit shed, which led to this bee house build...

The aim of most solitary bee house designs should be to...

• Provide a safe place for solitary bees to nest.
• Provide somewhere safe for new adults to emerge in the Spring
• Allow easy access to cocoons for collection and cleaning at the end of the season.

This is my v1.0 bee house attempt:

Bee house in situ

Here is this some of the 2020 batch waiting to hatch in Spring 2021 

Here is a male hatching early season 2021.  I love the drawer since I can easily open it without much disturbance, it also makes filming this happening is really easy to do:

Hole-nesting solitary bees will use a variety of nest sites, all are variations on a long narrow opening into which nesting chambers are constructed.  Examples include:

1. Bamboo canes: Variable sizes kept in a container of some kind.  Can source yourself or get online.  Disadvantages are you cant collect cocoons so allows disease, predator and parasite build up over time.
2. Reeds: As above, but may be able to split to get the cocoons out.  
3. Drilled blocks/logs.  Same issues as bamboo
4. Cardboard tubes with paper liners.  **NEW** Update spring 2021, I got a starter set from masonbees.co.uk, see here
5. 
   
6. 

   

   My masonbees.co.uk holder in situ

   
   
   
   
7. Stackable trays with pre-cut channels.  Channels cut into flat pieces of wood that are stacked, e.g.  https://crownbees.com/, wildlifeworld.  This option came out on top, with cardboard tubes a close second.

Life-cycle 
Female bees collect pollen.  Female bee deposits the pollen in an appropriately sized hole.  She then lays an egg and closes up a chamber containing egg+pollen with a mud wall .  She repeats the process until the hole is full with multiple chambers.  In the Summer the eggs develop into larvae, feed on the pollen stores and develop into a cocoon.  In the following Spring the new bee emerges from the cocoon.  Males emerge first so that they're available to inseminate the females, who then go onto to perpetuate the life-cycle.

This v1.0 design is based on the stackable tray type.

• Longer holes produce more females.  Females do more pollinating than the males (who hang about at the beginning of the season to inseminate the females then die).  We made 7.5 inch long trays, with the channels cut right to the end.  Some websites had examples up to 11 1/2 inches long, but I had limited timber stocks to work with!
• Channels are 5/16 inch deep and 3/8 inch wide, which is the recommended size for mason bees.  I used this 1/4" square-end router bit.  I wanted a round ended (or 'bull nose') bit but couldn't find one the right size that didn't cost the earth.
• Trays were cut from one piece of 18x199x2400mm pine (mixing imperial and metric, sorry), so I got 12 trays out of one piece.
• Each tray has 8 channels giving 96 channels in total
• Rather than routing these individually which would be a pain, I just routed the wood into one very long tray and then cut that into sections.

• As the channels go through to the back, there's a piece of cardboard folded over the back end (as in this video).
• The front of the block is unevenly scorched, as this apparently that helps them find the correct hole.  Other variations of this include marking the front, or using differing colour trays.

Stacked tray block before and after scorching

• The stack is bound together by a tie down strap with metal cam buckle (I had to google the proper name for that) picked up from the local DIY shop, but can be sourced elsewhere.
• There's an 'emergence drawer' at the base for any cocoons we collect this year (prob a bit late, may get a batch in for next Spring).  This gives a safe place for adults to emerge.  The holes in the front allow the newly emerged bees out (drawer would be closed...).

Safe place for new adults to emerge from cocoons in  the Spring

• A South-Facing position is recommended, we settled for S-SE 

The effect of scorching is more obvious in this pic

The box housing the bee block is made from 'stuff lying about', but mostly is 6mm ply and finished with a coat of linseed oil.  No oils / preservatives are applied to the blocks themselves.

Most of the solitary bee info stuff that I could find in the web dealt with Mason bees, but there are many others which presumably have their own nesting preferences.

Some links that I found useful
http://nurturing-nature.co.uk (watch them build, had a spot on Springwatch 2018)
http://cvgss.org/mason-bees/
https://crownbees.com/
https://beekeepclub.com/crown-bees-mason-bee-house-48-hole-wood-nesting-tray-kit-review/
https://www.masonbees.co.uk/product-page/bee-lodge
https://threehundredandsixtysix.wordpress.com/2013/02/01/green-steps-building-a-mason-bee-house/

...so no tech in this one, but I like the idea of this bee counter discussion thread, which aims to count honey bees activity around a nest entrance hole using a raspberry pi camera... Could theoretically apply the same approach with a down-facing camera on this box...