Bumblebees launch a three-stage defensive response when their nest is disturbed

(Press-News.org) Bumblebees respond to physical disturbance of their nest with a sequence of defensive behaviors that lasts up to 10 minutes, according to a study by Sajedeh Sarlak at the University of Konstanz, Germany, and colleagues, publishing December 3, 2025 in the open-access journal PLOS One.

Although we often think of bumblebees as docile, friendly garden visitors, they will fiercely defend their nest if needed. Bumblebees are important pollinators for both wild plants and crops, and they are often kept in commercial greenhouses, so understanding their defensive behavior is important for both conservation and health and safety. However, relatively little is known about how they respond to nest disturbance.

To investigate, researchers studied commercially reared bumblebee (Bombus terrestris) colonies in the laboratory. They disturbed the bees with a mechanical jolt — mimicking an attack by a badger or a human — and collected video and audio recordings of their response. When the nest was disturbed, the bees immediately sprang into action, moving around faster, patrolling the nest, flying and climbing the nest walls, suggesting that they were searching for the source of the disturbance. This state of heightened activity lasted for several minutes.

Immediately after the disturbance, bees also often buzzed their wings or raised their legs. Leg-lifting is a warning that they are ready to sting, whereas buzzing might alert other bees to the threat, or serve as a warning to the intruder. Between 1 and 3 minutes after the disturbance, bees began grooming themselves and making short, rhythmic sequences of buzzes. These behaviors may have a calming effect, reducing stress after the threat has subsided, though the authors note that this buzzing could also serve to maintain alarm, and further study is needed before conclusions can be drawn.  

The results show that when their nest is disturbed, bumblebees respond by preparing to defend the nest, searching for the threat, warning potential intruders to stay away, and finally, recovering from the stress of the disturbance. They maintain a state of heightened vigilance for around 4 minutes, which may help them to react quickly if the threat returns. The study provides a comprehensive overview of bumblebee defensive behavior, which is a starting point for future research, the authors say.

Morgane Nouvian adds: “To me, this study is really a starting point. We describe the sequence of responses that follows a disturbance, and in doing so we are raising so many questions! What are the functions of these behaviors? Is this defensive response regulated by social or environmental factors? Some behaviors are not performed by all bees, are these responders specialized in defense?”

 

 

In your coverage, please use this URL to provide access to the freely available article in PLOS One: https://plos.io/4i9YeZO

Citation: Sarlak S, Ramesh D, Ashouri A, Goldansaz SH, Schwarz A, Seitz L, et al. (2025) Colony defence in bumblebees (Bombus terrestris). PLoS One 20(12): e0335136. https://doi.org/10.1371/journal.pone.0335136

Author countries: Iran, Germany

Funding: This research was supported by the Zukunftskolleg at the University of Konstanz and by a grant from the University of Tehran Research Vice-Chancellor, Ministry of Science, Research and Technology, and Iranian National Science Foundation (project number 97011974). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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