Honey bees have an impressive ability to regulate temperatures inside their hives, but new research suggests that extreme heat can push this natural cooling system beyond its limits. A study published in Ecological and Evolutionary Physiology found that prolonged heat waves can disrupt hive temperature control and contribute to declining colony populations.

Researchers monitored nine honey bee colonies in Arizona during a three-month period when temperatures frequently exceeded 104°F (40°C). Although the bees kept average brood temperatures near the ideal 93–97°F (34–36°C) range, temperatures fluctuated substantially throughout the day. Bees developing near the center of the brood experienced several hours outside the optimal range, while those near the edges spent nearly eight hours each day exposed to potentially stressful temperatures.

The effects were particularly pronounced in smaller colonies. Temperature fluctuations near the outer brood areas reached about 20°F (11°C) in the smallest hives, compared with roughly 11°F (6°C ) in the largest colonies. Larger colonies have more workers available to carry water, fan their wings, and ventilate the hive, giving them a greater capacity to control heat.

The researchers found that colonies exposed to higher peak temperatures and greater internal temperature swings experienced population declines. Humidity could make the problem worse because moist air reduces the effectiveness of evaporative cooling, the primary mechanism bees use to remove heat.

As climate change increases the frequency and intensity of heat waves, beekeepers may need to provide supplemental water, shade hives, improve insulation and hive design, and ensure colonies have access to high-quality forage. Protecting honey bees from extreme heat could become increasingly important not only for beekeeping, but also for agriculture, where pollination services support many important crops.