Bee bricks are an item that has gotten a lot of media attention after a town in the UK passed a law requiring them in all new buildings over a certain height. But as covered in The Guardian in 2022 in an article titled "Brighton bee bricks initiative may do more harm than good, scientists say", there are some legitimate concerns over their design.

The two main reasons for the concern are how difficult they are to maintain, and whether the holes are the correct depth that are required by native bees. For these reasons, we have chosen a different path for our solitary bee nest designs.

The Hole Depth Concern

One aspect often brought up is that the holes in bee bricks are only a few inches deep, since they are constrained by the depth of the brick itself. The reason this is an issue is that some species of wild bees choose the sex of their offspring when they are laying eggs inside the cavity based on how deep inside the hole they are. They will put females near the back and males near the front because the females take longer to develop. If the holes are not deep enough, she may skew her offspring toward more males than females, which can have an impact on the population when they emerge as adults.

There are a couple of studies linked at the bottom of this page that looked into this behavior for the leafcutter bee Megachile rotundata, and the mason bee Osmia lignaria (aka the Blue Orchard Bee). In general, what was found was that there is indeed a relationship between hole depth and the sex ratio of offspring, and that hole depths between 4" and 6" were suitable for both species, with depths closer to 6" being more optimal.

The Maintenance Concern

While the requirement to clean out the bee bricks each year for bee health reasons is often overstated (nobody is cleaning them out in the wild, after all), there are some valid concerns over using a design that is permanently mounted in a wall or that otherwise cannot be easily taken apart.

With nature, things don't always go as planned:

You may find nesting sites taken over by spiders, ants and earwigs, among other animals;
A nest may have high mortality, resulting in the front plug not being opened the following season because nothing has emerged, which prevents it from being reused; or
Parasitic wasps may take over many of the nests over time, requiring you to clean them out to start the nesting site over to make it suitable for bees again.

For these reasons, it's a good idea to create a design that is easy to clean out so that you can keep the location a good place for wild bees.

The Bottom Line

While topics in science will always have people on both sides of the debate (just as there are in the linked article above), we don't see any reason to reinvent the wheel here. There are well established and time-tested designs that have been used by scientists for decades that do work and that do not have the drawbacks that bee bricks do.

To toot our own horn, the bee blocks we make at Scopa - which are based off entomologist Karl Krombein's design from the late 1960s - do not have the shortcomings mentioned above. Our blocks also come with the benefit of being able to remove them individually to protect them from predators and other animals that don't have the bees' best interests at heart, which increases the odds that the young make it to the following year. And since they're made of white oak, you can reuse them for many years, and give them right back to nature when they're at the end of their life.

Factors affecting the sex ratio and nesting behavior of the alfalfa leafcutter bee by Dr. Henry Gerber and Dr. Edward Klostermeyer from 1972
How to Manage the Blue Orchard Bee by Dr. Jordi Bosch and William Kemp from 2001

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