citizen science - free-living bees

I’ve been poking around the internet for the next interesting journal article. This month, I typed citizen science + honeybee into Google Scholar, and one paper really stood out: “Monitoring free-living honeybee colonies in Germany: Insights into habitat preferences, survival rates, and citizen science reliability.”  The study compares research-grade observations of free-living honeybee colonies around Munich (N=107), with observations from a much larger citizen science project across Germany (N=423). Where possible, the authors aim to combine high-quality research data with citizen science observations to expand the geographic scope of the study. 

Free-living honeybee takeaways

• 63% of colonies nest in large-diameter, mature trees
• 31% nest in buildings

Why survival was overestimated
Colonies monitored directly by researchers in Munich showed only about 12% overwinter survival. Citizen scientists reported much higher survival (around 29%), but this turned out to be biased due to fewer follow-up reports and poorly timed observations.
Many “surviving” colonies reported by volunteers were actually new swarms discovered early in the season (46% overlapped with the swarming period).
Abandoned nest sites were often not reported, making colonies appear longer-lived than they really were.

Cavity entrance direction: buildings vs. trees
Radar plots show that:

• Tree cavities have a strong preference for south-facing entrances (20%)
• Building cavities show a preference for west (22%) and south (16%)

Cavity entrance height: buildings vs. trees

• Median entrance height for tree cavities: 4 meters (13.1 ft)
• Median entrance height for building cavities: 6 meters (19.7 ft)

Big-picture takeaway
What are your swarm trap plans for 2026? Will they look like unused bee equipment stacked on blocks, or purpose-built swarm traps raised and baited with pheromones? Does this study change how you’ll deploy your traps?  When building and tree cavity entrance direction are combined, even an unlikely north-facing entrance appeared about 10% of the time. In other words, it’s surprisingly hard to get this wrong. From a next-door homeowner’s perspective, having a swarm-trap plan—any plan—is far better than having none at all.

Feral Honey Bees in Urban Environments

 

Above: Exterior view showing the window shutter from outside.
Below: Interior view of the window shutter box with the access panel removed.

Introduction to the Citizen Science Article Earlier this year, I uploaded a photo of a local Atlanta bee nest entrance—found in a cut-off sycamore limb—to the Free Living Bees website. Not long after, I came across a fascinating citizen science journal article featured on the same site. As someone obsessed with swarms, I found it absolutely captivating.

Urban Population Density The research focuses on the city of Belgrade, Serbia—a large and densely populated urban environment. Residents reported both honey bee nests and swarms, often seeking help with their removal. Interestingly, the number of reports increased exponentially with population density (a relationship shown clearly in the paper’s data).  To verify and expand on these reports, the authors conducted phone interviews with the residents and followed up with on-site field studies.

Reported Swarms vs. Nests At first, I assumed that reports of swarms and nests would occur in roughly equal numbers—but not so. The study found 261 swarms compared to only 90 nests, meaning swarms were reported nearly three times more often.  Most swarms (about 78%) were seen at heights between 1–9 meters, remarkably similar to what Seeley describes in Honeybee Democracy (p. 52). Reported nest heights, on the other hand, were concentrated between 3–15 meters (about 74% of cases).

Interior–Exterior Shutter System Jovana Bila Dubaić kindly sent me photos to help clarify the distinction between (1) the wooden window shutter and (2) the wooden window shutter box. Many buildings in Belgrade feature a combined interior–exterior shutter system.
When closed, pedestrians see the wooden window shutter covering the exterior. When retracted, however, the shutter rolls upward into a wooden box located inside the building, above the window. Astonishingly, 30.7% of reported nests were found inside these shutter boxes.

Exploring with Google Street View Curious, I used Google Street View to explore some of Belgrade’s most populated neighborhoods—imagining myself as a scout bee. What I “saw” was extraordinary: street after street lined with windows that offer easy access to those wooden shutter boxes. From a bee’s perspective, it’s a smorgasbord of indoor nesting opportunities.

In summary Don’t be intimidated by the lengthy title: “Unprecedented Density and Persistence of Feral Honey Bees in Urban Environments of a Large SE-European City.” The paper is well worth the read, and if you reach out with questions, you’ll likely find that the lead author, Jovana Bila Dubaić, is remarkably generous with her responses.