The Hidden Bees of Our Cities: Reconnecting People and Nature Using Citizen Science

By Sage K. Naidoo

PhD Candidate | School of Animal, Plant, and Environmental Sciences | University of the Witwatersrand

Rapid urbanisation across the globe continues to reshape natural environments, affecting both the biodiversity that exists within these spaces and the way in which we occupy and interact with nature^1,2,3. As cities expand, opportunities to engage with nature can become increasingly limited^2,3, which be increasingly prevalent when it comes to the smaller, and often-overlooked, species that exist alongside us.

UrbanBEE South Africa set out to explore and transform our relationships with nature by giving people an opportunity to become custodians within their own natural spaces. Through participation in a citizen science project, people were encouraged to create a stronger connection to nature in a world where everyday interactions with biodiversity have become increasingly sparse.

At the heart of the project are solitary bees. Despite being less well known than honeybees, solitary bees actually comprise ~90% of our global bee population, with ~1 300 solitary bee species in South Africa alone^4,5. Unlike honeybees, solitary bees do not live in large colonies or produce honey^4,5. Instead, solitary bees are those where individual females build and provision their nests on their own. These tend to be within natural cavities in nature, such as inside hollow stems, cracks, holes in wood, or in artificial structures, such as the incredible bee hotels produced by Tutus Loco. Regardless of these biological differences, solitary bees are still remarkably important pollinators, playing key roles in the pollination of vegetation and crops across different landscapes^6,7. Thus, within our urban spaces contribute towards sustaining and supporting biodiversity through greening our cities and making them more resilient^8,9.

In South Africa, UrbanBEE found new homes for 510 bee hotels with residents across the cities of Johannesburg and Cape Town (Figure 1a). Using these bee hotels, we have been able to monitor the patterns of solitary bee activity across these cities in an attempt to understand two key factors:

1. How our urban environments shape the patterns and diversity of solitary bees, and

2. How bee hotels may serve as a way to understand social perceptions of, and connections to, urban nature.

Figure 1: A breakdown of the (a) number of bee hotels distributed to citizen scientists, and subsequently the activity habits of participants in the cities of (b) Johannesburg, and (c) Cape Town. This includes proportions of active participants, rate of attrition, and records that were removed due to limited information from participants.

Over a 17-week data collection period, which involved participants submitting a single photograph of their hotels each week, we were able to create a rich dataset that helps us to answer these questions. Over the data collection period, a total of 436 participants submitted at least one observation during the project period, with 292 active participants in Johannesburg and 147 in Cape Town (Figure 1 b & c). While participation naturally fluctuated over time in both cities, particularly during the December holiday period, the project ended on a strong note with a rise in submissions during the final weeks following additional engagement with participants (Figure 2).

Figure 2: Patterns of the active submission of data from participants in the cities of (a) Johannesburg, and (b) Cape Town over the 17-week data collection period indicating peaks and dips in citizen science activity during the project.

The preliminary ecological patterns emerging from the UrbanBEE South Africa have already been fascinating. In both cities, we observed an increase in solitary bee activity over time, reflected in growing numbers of sealed cavity nests within bee hotels (Figure 3 & 4). Patterns of occupation varied between the cities with Johannesburg starting off strong with much occupancy in the first week of collection (Figure 3), while Cape Town was initially slow to start (Figure 4). Eventually, however, both cities found their rhythm, and we observed more and more hotels gaining occupants as the weeks went by.

Figure 3: Heat map displaying patterns and records of increasing solitary bee occurrence across the City of Johannesburg over 17 weeks of data collection.

Figure 4: Heat map displaying patterns and records of increasing solitary bee occurrence across the City of Cape Town over 17 weeks of data collection.

Aside from abundance patterns, these preliminary results also highlight clear differences in the dominant functional groups present between the cities of Johannesburg and Cape Town. Johannesburg was largely dominated by occupants classified as “Other”, which included solitary wasps among other unidentifiable occupants. But the predominant solitary bee functional group present in this city were the Allodapula sp. (Figure 5). Contrastingly, Cape Town showed a greater prominence of Membrane and Leafcutter bees (Figure 6). In general, carder bees tended to be least commonly recorded group in both cities but appeared to show distinctive patterns of sudden increases followed by more stable occupation in the bee hotels.

Figure 5: Cumulation curves displaying the increasing accumulation of the main functional types of solitary bees recorded across bee hotels in the City of Johannesburg over 17 weeks.

Figure 6: Cumulation curves displaying the increasing accumulation of the main functional types of solitary bees recorded across bee hotels in the City of Cape Town over 17 weeks.

These findings highlight that cities are not uniform environments. Different climates, vegetation types, urban forms, and regional species pools can all shape the biodiversity we see within urban spaces. The slower start in Cape Town, for example, may be linked to cooler temperatures, stronger winds, and differences in the types of solitary bees found in the region at the start of the citizen science initiative.

Perhaps some of the most exciting outcomes of these preliminary results from UrbanBEE South Africa, however, is that is has not only been an ecological observation, but something that has roots within social perception and value.

Following the project, participants completed a post-intervention questionnaire focused on their experiences, knowledge, and perceptions of solitary bees and urban nature. Many participants reported that they noticed nature more frequently after taking part in the project (Figure 7a), gained a better understanding of solitary bee biology (Figure 7b), and developed a greater appreciation for the value of these often-overlooked pollinators (Figure 7c).

Figure 7: A breakdown of the proportion of citizen scientists (n = 215) who experienced changes in noticing, knowledge, understanding, and values of urban nature and solitary bees relative to patterns of (a) general urban nature, (b) solitary bee biology, and (c) solitary bee value after participating in the UrbanBEE South Africa citizen science initiative.

While these patterns alone highlight the value and impact of our research initiative, they are also supported by individual sentiments shared by our participants reflecting on the emotional and social value of taking part in such a project. For example:

• “A chance to learn more about the pollinators in my garden, who I previously didn't focus on much”

• “It was a fun, collaborative, child-friendly and educational activity that made my daughter and I feel like we were doing something interesting and relevant to support the natural world around us.”

• “It was exciting to see different types of bees using our hotel and to learn how to distinguish them.”

• “Satisfaction of still being able to contribute at 82!!”

• “A 4-month journey or discovery, engagement and excitement.”

• “I was excited and able to connect with friends and family around what was happening in their bee hotels”

• “That small seemingly insignificant actions…can have lovely big knock-on effects for nature”

• “It meant being part of a bigger campaign that will move the world ever so slightly in the right direction”

These responses reinforce one of the key ideas behind UrbanBEE: that citizen science is not only a tool for collecting ecological data, but also a way of reconnecting people with the smaller forms of nature around them.

While these patterns are very exciting, UrbanBEE does, however, extend beyond South Africa. With international collaborators working across multiple cities in Europe, this project aims to build upon this foundation at a global scale, and we cannot wait to see what patterns emerge from these landscapes. By using shared approaches across different urban environments, UrbanBEE is creating a platform that showcases the value of collaboration between researchers and the public.

Ultimately, UrbanBEE aims to demonstrate the importance of urban biodiversity using solitary bees as a focal group, while also helping reconnect people to nature, one small patch of nature at a time.

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