The Bees Beneath Our Feet: Exploring the hidden world of pavement‑nesting bees (Ep. 81)

A city sidewalk can look like the most lifeless place in the world—flat, grey, sealed. But beneath those thin seams of sand between the stones, entire insect neighborhoods are quietly thriving. Berlin’s pavements, it turns out, are home to dozens of species of ground‑nesting bees, wasps, and ants, many of them living right under the feet of people who never think to look down.

Dr. Sophie Lokatis joins us to discuss her study that revealed a few surprising truths about urban nature. A single stretch of pavement can host more than 60 species, and the presence of high‑quality floral resources, not the amount of green space, has the biggest impact on how many insects settle in. Pavement cracks also offer stable, protected nesting sites, sometimes outperforming the city’s so‑called “green” areas. And once you learn to spot those tiny sand piles and pin‑sized holes, you start seeing them everywhere—evidence of a hidden city that’s been there all along.

Dr. Sophie Lokatis works in the Institute of Biology at the Freie Universität Berlin in Germany. Her main interests lie in biodiversity research, urban ecology and education for sustainable development. She collaborated on this study with Claudia Weber, Grégoire Noël, Wiebke Sickel, Michael T. Monaghan, and Aletta Bonn.

Good to know

Sophie noted that their project builds on a previous Brussels study exploring how bees interact with urban pavements. She also mentioned Henri Fabre, the French naturalist often called the “father of modern entomology,” whose work inspires Alexander Fürst von Lieven, who started the pavement watching trend at Sophie’s office.

And if you are now inspired too, join this iNaturalist project and start mapping the bees nesting in your neighborhood’s sidewalks.

Transcript

[00:00:00] Welcome to the Bees Knees a podcast wild about native bees. Wild and native bees are under threat worldwide. In each episode, we look at actionable things we can do to support these adorable little guys whose pollination work is crucial for maintaining biodiversity. I’m Jacy Meyer and I thank you for being here.

Imagine walking down your city street, coffee in hand may be on your way to work, and realizing that the cracks beneath your feet aren’t just cracks they’re doorways. Tiny front doors to an entire hidden neighborhood of bees, wasps, ants, and flies quietly living their lives in the seams of our pavements.

Turns out many city pavements are buzzing with far more life than most of us ever notice. In today’s episode, I’m talking to Dr. Sophie Lokatis about her study that uncovered 66 species [00:01:00] of ground nesting insects living in Berlin sidewalks. And what she and her team found flips a lot of our assumptions about urban nature.

For example, more green space didn’t necessarily mean more nests. Instead, the quality of nearby floral resources, not the quantity of green cover, was what really shaped these miniature pavement ecosystems. We talk about why pavements can actually be valuable nesting habitat, how insect friendly gardens supercharge biodiversity, even in heavily sealed in landscapes, and why cities might be underestimating the ecological potential of the very ground we walk on.

So urban pavements aren’t exactly the first place most people imagine when they think of bee habitat. What sparked your curiosity to look there and what did you expect to find before you began? Yeah, that’s very true. So a couple of years ago, one [00:02:00] of our senior researchers from our institute, he used to spend his breaks in front of our building, and I met him there quite a lot.

And after a while. It became quite normal to walk into a group of people sitting in front of the building on the ground, staring together at the pavement. And now you wonder what they did. So they just stared there and looked at the insects crawling there. And so this researcher, um, his name is Alex. He had quite a passion for Henri Fabre who is this French naturalist who used to observe insect behaviors.

And Alex also is really into looking at the behaviors of small, tiny creatures. So our colleagues and these people from our building, we just started spending our breaks there and. Sort of obsessing about the behavior of these small insects. And these were mainly solitary wasps and ants and bees. And they were building their nests and carrying prey um, transporting pollen.

And then a bit later, Alex recruited two [00:03:00] students who did an inventory of the species inhabiting the pavement in front of our institute. And these two students, they found 17 species living on about, let’s say 200 meters of pavement around our building. I think they spent like two and a half months going there every week.

And so this was quite a surprising amount, a number of species they recorded. And by then I also had really become hooked on this topic. And so the thing about insects, nesting and pavement is that once you see them, you start seeing them everywhere. And it was so eye-opening and I couldn’t walk through the city of Berlin seeing these tiny holes everywhere.

So then when Claudia Weber, who was the first author of our study, she joined our group, was a master’s student, um, and she was looking for a project. We were already excited to turn this weird lunch break of session into a small study. [00:04:00] So how you did the study is your team combined the nest entrance monitoring with molecular tools like e-DNA.

Could you walk us through how you actually did this from choosing the pavement sites to identifying which species were living beneath your feet? Yes, of course. So first of all, we selected transects of pavements along an urban gradient in Berlin, and some of these pavements were situated in more urban areas.

These were highly sealed and others were much greener. Of course, we had to reach them. So they are not so widely distributed across Berlin because we were only a very small team. So they are mainly along the, uh, tram line in Berlin. But we tried to select them as random as possible and covering this urban gradient or, or rather these categories of sealing.

So one category was, um, pavements in an area that was highly sealed and the [00:05:00] others in greener areas. And in addition, we had pavements that were within reach of a flower rich garden and these gardens were, these gardens were designed to enhance biodiversity and in particular, pollinators. So this was sort of a third group of these transects.

And then we had the chance to work together with the Berlin Center for Genomics and Biodiversity Research, which have one of the buildings right across the street. And this allowed us to also look for traces of e-DNA . And the interesting thing about this is that one major problem with our project is that when you want to assess the diversity of bees and wasps nesting in these pavement cracks, you can spend hours just sitting there.

And look at the hole in the pavement and just spent hours waiting in front of this tiny hole and nothing happens. And if you’re lucky, an insect appears. So this is the reason why there was two students [00:06:00] in the first trial that spent two months of a research project. Just looking at this one pavement because they could go there every day and spend hours sitting on the pavement.

But we didn’t have this this time. So the idea was to look for traces of DNA in the sand from the entrance holes. Unfortunately, this part didn’t work as well as we hope, but then again, we didn’t have the resources to test this very systematically. I still think it could lead to a really cool citizen science project, though, which the people sending in small probes of sand or soil.

But this is. Sort of a dream project maybe for the future. But back to our study. So apart from identifying insects on the pavement transects, we also counted entrance holes of bees and wasps. We had to include ants because they form very complex subterranean nesting structures. And these structures have multiple entrances, so it’s impossible to count the number of nests for ants.

But bees and solitary wasps, [00:07:00] they always have just one entrance. You can just count them and assess how densely populated the pavements are. So you mentioned that one of the sites was near this pollinator friendly garden area, and you found that this area hosted far more nests and higher species richness.

What does this tell us about how urban design and small scale gardening choices can possibly influence bee communities? Yeah. For me, that’s the most important finding of our study because not only were there more nests and more diversity close to these insect friendly gardens, so what really surprised me was that there was no difference between highly sealed areas and green areas.

The only difference was when there was one of these biodiversity friendly flower rich gardens, and this actually tells you a lot about the quality of Berlin’s green spaces because. They are basically [00:08:00] green deserts with only little benefit for biodiversity. And on the other hand, we can see that these insect friendly flower gardens really work in providing foraging resources for bees and resources for other insects.

But increasing resources is not enough. A large fraction of bees and solitary wasps needs open soil to build their nests. And the Berlin pavement seems to be very attractive for them. So based on that, do you see pavements as genuinely viable nesting habitats for ground nesting bees and wasps? Or do you think it’s more accidental refuge created by human infrastructure?

That’s a very good question. There’s only very little research about ground nesting insects living in human made pavements. Apart from a second group of similarly enthusiastic entomologists from Brussels, we only know of one study from the eighties by one wasp researcher who did a study. I think he must have also done [00:09:00] it in his free time walking to his office.

He did a study in a city called Oldenburg, and this study made it into one of the first German textbooks on urban ecosystems. And there there’s a text fragment where there’s a section where the pavements are called habitat, which translates to preferred habitat for bees and wasps. And our colleagues from Brussels make a similar argument.

They say the pavement tiles provide protection from disturbance , and even if the entrance hole gets buried, the underlying tunnel system is still well protected. So these, um, pavement tiles, they protect the nest from, for example, intense sunlight, but they can also store warmth. I’m a bit cautious actually in calling pavements top habitat because if you compare to open sandy soil.

You’ll only find a fraction of the buzzing activity you find there. So it’s a question of which habitat you compare to. So many conservation efforts [00:10:00] focus on planting flowers, but your work reinforces the importance of the nesting sites too. What practical steps can us urbanites as well as cities take to support urban bees?

Beyond providing these floral resources. Patches of open soil can be extremely rare in cities. They can get covered by vegetation very quickly and just be lost as a viable nesting site. So a crack on the other hand, the crack in the pavement stays open all the time because people walk on top of it. And sometimes, like in Berlin, you have an entire net of sandy cracks between the cobble stones and tiles.

And this can actually be a great alternative to creating open sandpits, for example. There have been studies about wild bees in cities and these show that there’s an increase in cavity nesting bees towards the center and a decrease in soil nesting species, also towards the city center. And the reason for this is that many cities are [00:11:00] covered in asphalt and concrete towards the center.

So there’s this gradient of wild bee behavior changing a bit towards the city. I’m, I’m pretty sure you covered this also in the podcast, but interestingly, we could not find this pattern in Berlin. And I’m now talking about the different study, not the pavement one, but we also had a study looking at bee traits throughout Berlin.

And this pattern, which is typical for many other cities, we cannot find it here in Berlin. So luckily in Berlin at least, there’s still enough open soil and maybe also pavement cracks, which maybe serve as an alternative nesting habitat. So a while ago I was walking through Paris and they have. Many programs to enhance biodiversity also in the city center.

And I really enjoyed all the beautiful native flower patches there. And these are provided by the city administration, but if you turn around, there’s concrete everywhere. And also really few bees, in my opinion. [00:12:00] Of course, I didn’t compare directly, but I think what they are missing is this open soil. And I’m pretty sure this is the case for many, many other cities.

So in Berlin we are really lucky. And I think that getting rid of concrete and unsealing urban soils is a very, very good idea. Not only to have our bees, but this is a different tool. So in all your time working with bees and in biodiversity, has there been a discovery or some other part of your work that has given you hope or made you feel like you were making a difference?

Yeah. I must say that it’s our small pavement project. Um, which has always been just this small fun side project to our real work. But this has sparked a lot of interest, especially among people that have had very little connection with urban nature until now. And as I said in the beginning. Once you know about the small sandy hills that can be found below your feet, you’d start seeing them everywhere [00:13:00] suddenly.

I don’t know how it’s in your city, but Berlin seems to be a particularly good spot for bees and pavements. But I know that pavement cracks can be fascinating everywhere. Yeah. I think that once people learn about the life that’s below our feet, they start appreciating and maybe even protecting it. So yeah, the Berlin pavement is a very unexpected place for hope.

I absolutely love the inspiration behind this study. This image of the small group of people spending their lunch breaks with their eyes glued to the ground, peering into pavement cracks while the rest of the city rushes past. There’s something wonderfully human about that kind of curiosity and something wonderfully hopeful about what they found, because at the heart of this research is a reminder we really need right now.

Cities still have room for life. Even tiny pockets of open soil can become entire neighborhoods for wild bees. [00:14:00] And when we pair that with high quality floral resources, suddenly the pavement isn’t just pavement anymore. It it’s home. If you want to see what that looks like, head over to our website, the Bees Knees website, where you’ll see some photos of bees nesting, right in Berlin Sidewalks.

And if you’re feeling inspired to look down a little more often yourself. We’ve also linked to an iNaturalist project where you can upload your own photos of pavement, nesting bees. It’s a simple way to join this growing community of ground gazers. Until next time, don’t forget to greet the bees in the sidewalk.