How to help bees survive a heat wave
People aren't the only ones stressed by extreme summer heat — bees feel it too.
Honey bees maintain their hives between 32—36°C (89.6—96.8°F), and outside of this temperature range, honey bee larvae and pupae won't develop and may die. When temperatures are below freezing, honey bees maintain temperatures in their nests with the help of worker bees. Workers pack together on the outer edge to create an insulative outer shell to hold heat in the center of the nest.
The bees distribute droplets of water around the nest, which works in parallel with the fanning to create the equivalent of honey bee AC.
Honey bees are somewhat adapted to extreme heat. As soon as temperatures in a honey bee colony edges up beyond 96.8°F, worker bees line up at the entrance and start fanning their wings. In addition, a particular group of water-foraging bees begins scouring the surrounding area for water, which they collect and bring back to the nest. The bees distribute droplets of water around the nest, which works in parallel with the fanning to create the equivalent of honey bee air conditioning. As temperatures rise to extreme heat levels, more honey bees will start to forage for water.
Shallow trays of water with pebbles in the bowl may be placed outdoors or in the garden to support honey bees in a heat wave. The pebbles or small rocks keep worker bees from drowning in the water when they come for a sip.
How bumblebees maintain nest temperatures
Bumble bees may not be able to cool their nests as effectively as honey bees. Although bumble bees engage in fanning behavior during extreme heat events, they are better adapted to warm up their nests during cold spells. Large thoracic muscles allow bumble bees to produce heat by "shivering." Bumble bees' thick "fur" helps them retain heat in their bodies. These traits are considered adaptations that help bumble bees warm their hive and forage at lower temperatures.
Individual bumble bees have a remarkable amount of control of their circulatory and respiratory systems. This helps them conserve heat in their thorax when outside temperatures are cold (allowing them to fly at temperatures as low as 40°F) and "dump" heat into their abdomen when ambient temperatures creep above 100°F.
Bumble bees begin struggling to fly when temperatures rise above 100°F. In general, bumble bees begin struggling to fly when temperatures rise above 100°F, with smaller workers being less sensitive to heat extremes compared to larger queens.
There is limited information on how bumble bee colonies keep cool during heat waves. Although bumble bees have been seen collecting water, it's unclear whether it is used to cool their nests. As nest temperatures rise above 90°F, bumble bee queens and workers stop incubating the brood, move off the nest, and the workers begin fanning.
By fanning, bumble bees have been shown to lower the temperatures of their nests by 10°F (Gardner et al. 2006). Moreover, many bumble bee species nest below ground, providing some insulation from outside heat.
Select plants that support many types of pollinators
Sunflowers are a great example of a plant with an exceedingly long tap root that provides good food for bees even when the grass has turned brown.
During a heat wave, it's vital that nectar- and pollen-providing plants are not stressed and are ready to start working when the bees show up. Make sure to water your plants in the evenings and use a moisture probe to ensure your plants are not drying out, particularly in container gardens.
Additionally, select summer-blooming plants that do well under heat stress and don't need a lot of watering. For example, sunflowers are a great example of a plant with an exceedingly long tap root that provides good food for bees even when the grass has turned brown. Lavender is another reliable drought-tolerant plant that bumble bees adore.
Plant native plants that tolerate drought:
• Gumweed (Grindelia).
• Tarweed (Madia).
• Goldenrod (Solidago).
• Farewell to spring (Clarkia).
• Snowberry (Symphoricarpos albus).
• Ocean spray (Holodiscus discolor).
• Douglas aster. Douglas aster supported more bee species than other native plants tested in the OSU Garden Ecology Lab field plots.