Sampling 24 colonies across five apiaries, University of Sydney researchers found the hive’s antimicrobial materials are not scattered at random but organised in layers from the entrance inward.
That honey does not spoil has been known for as long as people have kept bees. So has the fact that propolis, the resinous material bees use to seal gaps, resists microbes, and that beeswax is similarly inhospitable. Each of these has been studied on its own.
What had not been examined is where in a hive they sit. Researchers at the University of Sydney sampled 24 honey bee colonies across five apiaries at Tocal College in New South Wales and found the arrangement is not incidental. Writing in ISME Communications, they describe the colony as a layered defensive structure.
“Hives are not only homes for bees, but also act as their workplaces, restaurants and hospitals, and now we can add immune systems to the list,” said Dr Kenya Fernandes, the lead researcher, an Australian Research Council DECRA Fellow in the School of Life and Environmental Sciences.
The surprise was the layout
“We already know honey, beeswax and propolis have antimicrobial properties independently,” Fernandes said. “But what came as a surprise was how these materials were placed in the hive wasn’t random, but organised.”
The pattern runs from the outside in. Hive areas exposed to the outside had the strongest defences: honey from those areas showed the most potent antimicrobial activity, and propolis was similarly strong.
Both are rich in bioactive compounds, and the two work differently. Honey’s activity comes partly from hydrogen peroxide, generated slowly by an enzyme the bees add to nectar — a broad, non-specific oxidant. Propolis is rich in flavonoids, plant-derived compounds the bees collect rather than manufacture, and which act through more varied mechanisms.
Putting the broadest-acting materials where the colony meets the outside world is the arrangement a designer would choose. Anything entering the hive, on a forager’s body or in the nectar she carries, encounters the strongest and least selective defences first.
More targeted toward the centre
Further in, the character of the defence changes rather than simply weakening.
“As we travel closer to the hive centre, the antimicrobial defences became more targeted, with wax comb, stored pollen, and the bee’s own bodies helping to filter out harmful bacteria and fungi, whilst encouraging helpful species,” Fernandes said.
Encouraging helpful species is the part that makes the immune-system comparison more than a metaphor. A colony that sterilised itself would be in trouble: the fermented pollen that bees eat, known as bee bread, depends on microbial activity, and the bees’ own gut communities matter to their health. A defence that kills indiscriminately at the core would destroy the colony’s food processing along with its pathogens.
The team sampled broadly to establish this, taking honey, pollen, beeswax and propolis along with the bees’ gut microbial communities, secretions and body tissues. Many of the bacteria and fungi found in hive materials likely arrived in floral nectar, which makes the filtering function concrete: the hive is continuously taking in microbes with its food supply and sorting them.
The innermost layers protect what matters most. “The hive’s antimicrobial properties worked together to protect the eggs and larvae, as well as the fermented pollen the bees consume,” Fernandes said.
Bacteria over fungi
One asymmetry stood out. The defences were more strongly tuned against bacteria than against fungi, which the researchers read as a cost-benefit trade-off.
The example they give explains the logic. American foulbrood is a bacterial disease of bee larvae and it is fatal — infected colonies are frequently destroyed outright to stop its spread, since the spores persist for decades in equipment. A colony facing a threat of that severity from bacteria, and milder threats from most fungi, is better served by investing where the danger is.
It is worth noting that this is the researchers’ interpretation of the pattern rather than something the study tested directly. An alternative reading is simply that hydrogen peroxide and the flavonoid mixtures bees collect happen to be more effective against bacteria, and the apparent tuning reflects available chemistry rather than allocation.
The defences depend on the landscape
The finding with consequences outside the hive is that these chemistries are not fixed. Hives near native bushland and hives near agricultural land had measurably different chemical defences.
That follows from where the ingredients come from. Flavonoids in propolis are collected from plant resins and exudates, and the compounds available depend on which plants are within flying range. A colony surrounded by a monoculture gathers from a narrower palette than one beside diverse bushland.
“This shows healthy hives depend on and are influenced by healthy ecosystems,” said Elizabeth Frost, a co-author and Technical Specialist Bees at the NSW Department of Primary Industries and Regional Development. “Land clearing and intensive farming could be quietly eroding the bees’ natural defences. This builds a strong case for protecting diverse flowering habitats that support healthy hives.”
Frost set that against the threats that get more attention. “There are direct threats to bee populations such as the varroa mite, but many don’t realise the indirect threats: the shrinking of healthy ecosystems has a domino effect,” she said. “Landscapes with diverse plant species can increase the bees’ chances of being resilient to disease.”
The study establishes that the chemistry differs by landscape. It does not demonstrate that colonies in cleared landscapes get sick more often, which is the step that would make this a management argument rather than a mechanistic one.
Whether other insects do it too
Fernandes would like to know whether the arrangement is a honey bee peculiarity or a general feature of social insects.
“I’d love to see if other social insects such as native stingless bees, ants and termites, which also build incredibly complex homes, also have the same system,” she said.
It is a reasonable question. Leaf-cutter ants cultivate fungus gardens and maintain them against invading moulds with antimicrobial secretions and symbiotic bacteria, and termite mounds host their own microbial communities. Whether any of them organise their chemistry spatially, as these hives appear to, has not been looked for.
The work was supported by a New South Wales Bushfire Industry Recovery Package Sector Development Grant and an Australian Research Council Discovery Early Career Award. Fernandes is a 2026 NSW Tall Young Poppy awardee. The release does not name the study’s other authors.
Notes
- “Spatially organised chemical defences shape microbial communities in honey bee colonies.” ISME Communications, 2026. DOI: 10.1093/ismeco/ycag247.
- University of Sydney. “Bee hives found to be ‘living immune systems’ that protect bees.” EurekAlert!, 19 October 2026. https://www.eurekalert.org/news-releases/1148202.
Photo by Pixabay on Pexels.com