I have received a number of emails, just like this one from Sara in the UK, asking about whether the reason she was seeing so few bees in her garden, might be down to a recent heatwave, during which temperatures were frequently reaching 25 - 30oC, accompanied by a relatively dry spell.
"Hi,
It's been so hot here lately, and my neighbour and I were wondering why we are not seeing so many bees about, especially on our lavender, but also they are not visiting other plants like Echinops.Do bees like it when it's hot outside, and are we missing the bees because of the very warm, dry weather?
- Sara, UK."
Do Bees Like It Hot? What Temperature Is Best For Bees?
According to one study by Kenna et al concerning bumble bees1, the average distance flown by bees was at its furthest when the temperature was at 24℃. The study also noted that foraging potential might be maximised at temperatures closer to 27℃. Kenna et al commented:
"Subsequently, while mean distance was highest in the 24℃ cohort, there were more successful fliers in the 27 and 30℃ cohorts, meaning that foraging potential at the colony level may actually be maximised at temperatures closer to 27℃."
What temperature is too hot for bumble bees?
When temperatures exceed27℃, Kenna et al1 note that flight performance begins to be negatively impacted. However, what is not clear is how such temperatures might affect foraging behaviour of bumble bees when in their natural environment, especially if temperatures were to rise in the longer term. For instance:
- are bumble bees more likely to vary the times at which they might forage for food, according to temperature? For example, will they leave the nest during the cooler parts of the day, such as morning and early evening? There is some suggestion that this may be the case.
- how might temperature affect the usual nectar secretion patterns from plants, and in turn, foraging behaviour?
At what temperature do bumble bees stop flying?
Kenna et al proposethatwhen temperatures rise to 35°C,flight distance could be reduced to under 1km.
They also observed that at temperatures of 15°C and below, bees frequently would not fly past 100m, and not more than a fewhundred metres.
Bumble bee on catmint
Are hotter temperatures a danger to bumble bees?
Frequency of extreme heat may pose a threat to some bumble bee species. For instance, a study2 of 66 bumble bee speciesacross North America and Europe states:
"Increasing frequency of hotter temperatures predicts species' local extinction risk, chances of colonizing a new area, and changing species richness."
How do bumble bees maintain nest temperature?
Bumble bees have been shown to maintain their nests at a temperature of 28°Cto 32°C, and workers may engage in wing-fanning when nest temperatures rise3.
What temperature is best for honey bees?
The optimum temperature for flight activity is 72-77º F (approx. 22 - 25oC, but activity continues up to about 100º F (37.7oC) before declining4.
The minimum temperature for honey bee flight is 54ºF (about 12oC) according to some sources, but this is debated, since honey bees have been observed to forage in cooler temperatures.
Can honey bee hives get too hot?
The optimum temperature for a honey bee hive is 32–36°C (89.6–96.8°F)5.
To prevent hives getting too hot, honey bees fan their wings and collect water to help prevent brood drying out6.
Honey bee collecting water
How Can I Help Bees In Hot Temperatures?
To help bees survive and thrive during heat waves and temperature extremes, follow these simple steps:
1. Safely provide water
Keep a shallow dish of pebbles or bird bath topped up with water. Pebbles enable bees to land and access the water.
2. Keep bee-friendly plants well hydrated
So that plants can offer pollen and nectar for bees, keep them well hydrated so that they don't dry out and die. It's best to water plants in the evening, or very early morning. If necessary, use bath water and even liquid left overs such as tea and coffee on your garden if there is a water shortage.
3. Add drought-tolerant plants to your garden
Some plants are especially tolerant of dry, hot conditions. Examples include ice plant (Sedums), golden rod (Solidago), Spirea,Snowberry (Symphoricarpos albus). See drought tolerant plants for bees.
4. Extend the flowering season
Careful selection of plants can help lengthen the amount of time flowers are available to bees, but remember that dead-heading existing specimens in your border, or leaving clover to flourish in the lawn and sowing a few quick-growing annuals can are simple methods to further extend the flower availability for pollinators.
Why have bees stopped visiting my garden?
References
1. Kenna, D., Pawar, S., & Gill, R. J. (2021). Thermal flight performance reveals impact of warming on bumblebee foraging potential. Functional Ecology, 35, 2508– 2522. https://doi.org/10.1111/1365-2435.13887. And: "Bee flight suffers under temperature extremes" - Imperial College London, 2021.
2.Soroye P, Newbold T, Kerr J. Climate change contributes to widespread declines among bumble bees across continents. Science. 2020 Feb 7;367(6478):685-688. doi: 10.1126/science.aax8591. PMID: 32029628.
3.Gardner, K.E., Foster, R.L. & O’Donnell, S. Experimental analysis of worker division of labor in bumblebee nest thermoregulation (Bombus huntii, Hymenoptera: Apidae). Behav Ecol Sociobiol 61, 783–792 (2007). https://doi.org/10.1007/s00265-006-0309-7
4.University Of Maine: Honeybee Flight Activity Index.
5. Daniel Cook, Boyd Tarlinton, James M McGree, Alethea Blackler, Caroline Hauxwell, Temperature Sensing and Honey Bee Colony Strength, Journal of Economic Entomology, Volume 115, Issue 3, June 2022, Pages 715–723, https://doi.org/10.1093/jee/toac034 - CitingTautz 2008, & Stabentheiner et al. 2010.
6. Madeleine M. Ostwald, Michael L. Smith, Thomas D. Seeley; The behavioral regulation of thirst, water collection and water storage in honey bee colonies. J Exp Biol 15 July 2016; 219 (14): 2156–2165. doi: https://doi.org/10.1242/jeb.139824
Why do bees need water, and what's the best way to provide it?
Why do bumble bees fly into windows?
Are Bees Smart?
As an enthusiast with a profound understanding of bee behavior and the impact of temperature on their activities, allow me to share my expertise on the concepts discussed in the provided article.
1. Bee Foraging Behavior in Relation to Temperature: The study conducted by Kenna et al provides valuable insights into how temperature affects bee foraging. Bees, particularly bumblebees, exhibit optimal foraging potential at temperatures around 27℃. The study suggests that while the mean distance flown is highest at 24℃, the number of successful fliers increases at 27 and 30℃, indicating that foraging potential at the colony level may be maximized at temperatures closer to 27℃.
2. Impact of High Temperatures on Bee Flight: Kenna et al also observed that flight performance of bumblebees starts to be negatively impacted when temperatures exceed 27℃. At 35°C, flight distance could be significantly reduced to under 1km, posing potential challenges for bumble bees during heatwaves.
3. The Effect of Temperature on Bumble Bee Species: Extreme heat events can pose a threat to some bumble bee species, as mentioned in a study across North America and Europe. The study highlights that increasing frequency of hotter temperatures predicts local extinction risk, colonization challenges, and changes in species richness.
4. Nest Temperature Regulation in Bumble Bees: Bumble bees actively regulate nest temperature, maintaining it between 28°C to 32°C. When temperatures rise, workers engage in wing-fanning to cool the nest, showcasing the sophisticated thermoregulation mechanisms employed by these insects.
5. Optimal Temperature for Honey Bee Activities: Honey bees have specific temperature preferences for flight activity. The optimum range is between 22 - 25℃, with activity continuing up to about 37.7℃ before declining. Honey bee hives also have an optimal temperature range of 32–36°C, and bees employ wing-fanning and water collection to prevent hives from getting too hot.
6. Impact of Climate Change on Bee Species: The article references a study indicating that climate change contributes to declines in bumble bee populations across continents, emphasizing the importance of considering long-term temperature changes in understanding bee behavior.
7. Providing Support for Bees in Hot Temperatures: The article concludes with practical tips for supporting bees during heatwaves, including providing water sources with pebbles for landing, keeping bee-friendly plants well-hydrated, incorporating drought-tolerant plants, and extending the flowering season.
In summary, the provided information covers a comprehensive range of topics related to bee behavior in response to temperature variations, highlighting the intricate relationships between climate, foraging patterns, and the well-being of bee populations.
