Water Collection in Honeybees: The Influence of Weather and Colony Size

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This study shows that water collection increases with colony size and on warm days. It also serves as a reminder that water is a basic resource for brood and the normal functioning of the colony. For the apiary, the message is straightforward: a reliable watering point is worth planning for, with appropriate caution given the semi-controlled experimental setup.

1. Key findings

The question investigated is: how do weather and colony size influence water collection, and is there a thermal threshold beyond which collection increases markedly?
Under semi-controlled conditions, large colonies collected more water on average than small colonies, with particularly high levels in spring and summer and a measured daily maximum of 1.39 L.
Above a mean daily temperature of 22.3 °C, or a daily maximum of 31.5 °C, water collection increases markedly, presumably to meet the brood's thermoregulation requirements.
The number of adult bees is the most explanatory individual factor: it accounts for just over 40 % of the observed variance in daily water collection, both below and above the threshold. Below the threshold, open brood explains a further 19 %; above it, maximum temperature explains a further 23 %.
The practical message for the apiary is useful but calls for caution: water should be managed as an active resource, without applying these findings as a universal rule valid for every Swiss apiary.

2. What the study shows

A study conducted in Avignon quantifies, under semi-controlled conditions, how colony size and weather affect daily water collection.

Fig. 1. Predicted trends in daily colony water collection as a function of meteorological factors when colonies were exposed to high ambient temperatures. Graphs show observed values (grey dots) and predictions (with 95 % confidence intervals) of daily colony water collection as a function of (a) daily maximum temperature (Tmax) and (c) daily global radiation (GR), respectively, for three levels of daily minimum relative humidity (RHmin). Conversely, graphs (b) and (d) show predictions of daily colony water collection as a function of daily minimum relative humidity (RHmin) for three levels of either daily maximum temperature (Tmax) or daily global radiation (GR). The three levels of the moderating variable are the mean and plus or minus one standard deviation (−1SD and +1SD), with all other covariates held at their mean.

Research question. Water is indispensable to the colony, not only for the production of larval food but also for brood cooling during hot periods. The authors therefore set out to measure directly the amounts of water collected at the level of an entire colony and to identify the factors that explain variation in collection: colony size, brood, and weather variables.

Method. The study was conducted under semi-controlled conditions in net-covered tunnels that prevented access to other water sources and to external input via nectar. A total of 24 colonies were monitored over 73 days, in spring, summer, and autumn. Two colonies of different sizes were observed simultaneously, each with an open watering point to measure collection and a control watering point to correct for evaporation. Weighings were performed hourly. Colony size was estimated using the ColEval method, based on the number of adult bees and brood cells.

Results. Large colonies collected more water on average than small colonies across all three seasons. Mean daily values reached approximately 401 mL in spring, 639 mL in summer, and 123 mL in autumn for large colonies, compared with 202 mL, 320 mL, and 102 mL for small colonies. A daily maximum of 1.39 L was recorded in summer for a strong colony.

The authors identified a thermal threshold beyond which water collection increases markedly: 22.3 °C for mean daily temperature and 31.5 °C for daily maximum temperature. This increase is interpreted as corresponding primarily to the more pronounced onset of brood thermoregulation requirements.

The most robust finding is the role of colony size: the number of adult bees alone accounts for just over 40 % of the observed variance in daily water collection, both below and above the threshold. When the colony is not yet experiencing extreme heat, the number of open brood cells explains a further 19 % of the variance; when heat becomes intense, maximum temperature explains a further 23 %. The effect of heat is also amplified when the air is drier.

Interpretation. The study thus supports two complementary conclusions. First, water is not solely a heat-wave resource: it matters more broadly for the normal functioning of the colony, particularly for brood. Second, once a certain heat threshold is crossed, demand shifts to a different scale. The authors also show that the proportion of water foragers decreases as colony size increases up to approximately 13,000 individuals, then stabilises at around 0.13 %. This suggests size-dependent task specialisation, though individual-level specialisation was not measured directly.

3. Critical appraisal

The results are robust enough to identify general trends, but their direct application to a standard apiary requires several caveats.

Strengths. The main strength of the study is the quality of measurement: evaporation correction, hourly monitoring, comparison of colonies of different sizes, coverage of three seasons, and explicit modelling of weather variables. The identification of a statistically validated thermal threshold provides a practically useful reference point that is rare in the literature on this topic.

Methodological limitations. The experimental setup remains artificial. Colonies were kept in tunnels and deprived of external water sources as well as nectar input. The results therefore describe a controlled situation very well, but translate less directly to an open apiary where nectar flow, distance to the water source, shade, wind, aspect, and microclimatic diversity also play a role. Colonies were also fed ad libitum with pollen and fondant.

The proportion of water foragers must also be interpreted with caution. It was estimated from brief counts at the watering point; foragers returning to or remaining inside the hive at the time of counting were not included. This proportion should therefore be regarded as a minimum. Furthermore, the ColEval estimate of colony size remains a field approximation, even if standardised.

Potential biases and confounding. The authors themselves note that certain observations influenced the coefficients of the mixed linear models. They present results using the full dataset as well as supplementary analyses excluding these influential observations, which strengthens transparency but is a reminder not to over-interpret the precise numerical values.

Transferability. The study was conducted in Avignon, in a warmer and drier climate than many Swiss apiaries, particularly at altitude. The threshold of around 30 °C is a useful reference point, but should not be read as a universal and rigid boundary equally applicable to the Swiss Plateau, mountain sites, or heavily shaded apiaries.

What cannot be concluded. This study does not specify what capacity a watering point should have, what distance from the apiary would be optimal, or which water source would be best in all situations. It also does not directly measure the load brought back by each individual forager or the exact number of foraging trips. It demonstrates a biological dynamic that is valuable for practice, but does not in itself provide a universal management standard.

4. Practical implications for the apiary

At the apiary, this study reinforces the view that a reliable watering point should be treated as a basic resource, not as an incidental detail relevant only during heatwaves.

Ensure stable access to water from the start of the brood-rearing period, not only in midsummer.
Pay particular attention to strong colonies when days become warm and dry, especially in spring and summer.
Treat the reference values of 22 °C mean daily temperature or approximately 30–32 °C maximum as a practical signal of a possible increase in water requirements, not as an absolute rule.
A clean, attractive, and secure watering point fitted with floats or other devices to prevent drowning remains a reasonable measure.
For Switzerland, adapt the interpretation to the actual apiary context: altitude, aspect, shade, natural water availability, colony strength, and forage conditions can substantially modify demand for free water.

Read the original study

►Effects of weather and colony size on water collection in honey bee, Apis mellifera, colonies

Le Bivic, P., Alaux, C., Gay, C., Vidau, C., Le Conte, Y., Belzunces, L. P., & Pioz, M. (2025). Effects of weather and colony size on water collection in honey bee, Apis mellifera, colonies. Animal Behaviour, 227, 123271. https://doi.org/10.1016/j.anbehav.2025.123271

References

Author

Le Bivic, P., Alaux, C., Gay, C., Vidau, C., Le Conte, Y., Belzunces, L. P., & Pioz, M.

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