The question of whether bees are active after sunset is common, given their familiar presence during daylight hours. For the vast majority of the over 20,000 bee species worldwide, including the familiar European honey bee (Apis mellifera) and common bumblebees, the answer is no, they are strictly diurnal. These daytime foragers cease activity when the sun goes down, returning to their nests or hives to rest. However, a small, specialized group of species has evolved to work the night shift, demonstrating fascinating adaptations to a low-light existence.
The Diurnal Majority: Why Most Bees Rest at Night
The activity cycle of most bees is governed by two primary physical factors: temperature and light availability. Bees are cold-blooded, meaning their body temperature fluctuates with the environment, and they rely on external heat sources to function. To achieve the flight-ready temperature necessary for their thoracic muscles, a bee must warm its body to at least 30°C.
During the day, bees primarily absorb solar energy (ectothermy) to reach this temperature quickly, allowing for efficient foraging. When ambient temperatures drop after sundown, maintaining this internal warmth becomes energetically demanding or impossible, forcing them into inactivity. Below approximately 10°C, the risk of losing neuromuscular function and entering a chill-coma becomes significant, making night flight a serious hazard.
Reduced visibility and the availability of resources also limit nighttime foraging for diurnal species. Most flowers open and release pollen and nectar only during the day, relying on insects for pollination. Without daylight cues to navigate and with a scarcity of open flowers, the energetic cost of a nocturnal trip far outweighs the potential food reward.
Specialized Night Shift Workers: Nocturnal and Crepuscular Bees
A specialized group of approximately 250 bee species has evolved behaviors that circumvent the restrictions faced by the diurnal majority. This group is broadly categorized into crepuscular and truly nocturnal species, which are active during twilight or the full dark, respectively. Crepuscular bees, such as certain species of sweat bees (Halictidae) and plasterer bees (Colletidae), primarily forage during the brief, dim periods of dawn and dusk.
Truly nocturnal species, such as the Indian Carpenter bee (Xylocopa tranquebarica), are able to forage deep into the night, even under moonless conditions. These bees focus on flowers that bloom exclusively after dark, providing a resource niche free from competition. Examples include night-blooming cacti or certain tropical plants that offer copious nectar and pollen designed to attract moths or bats, which the nocturnal bees exploit. Some Ptiloglossa bees, for instance, visit flowers like Caryocar brasiliense, which opens in the evening and provides resources until dawn.
Sensory Adaptations for Low Light
The ability of these bees to navigate and forage in near-darkness is rooted in modifications to their visual anatomy. Most bees possess apposition compound eyes, a structure generally poor at gathering light. Nocturnal species have evolved much larger compound eyes with notably larger facet lenses and wider rhabdoms—the light-sensitive parts of the photoreceptor cells.
These modifications significantly increase the amount of light captured by each visual unit; for example, the eyes of the nocturnal carpenter bee are up to 27 times more sensitive than those of its diurnal relatives. Nocturnal bees also possess greatly enlarged ocelli, the three simple eyes located on the top of the head. While ocelli cannot form images, their size makes them highly effective at detecting subtle changes in light intensity, which aids in orientation and flight stability.
A key neural strategy that compensates for the low light is spatial summation. This process involves the nervous system pooling the weak signals from many adjacent visual units. This pooling increases overall light sensitivity and reliability but reduces visual acuity, resulting in a blurry but functional image of the night environment.
The Hive at Night: Activities Inside the Colony
For social species like the honey bee, night is not a period of complete stillness. Activity shifts from external foraging to internal maintenance and collective care. A primary nighttime activity is thermoregulation, where the colony acts as a unified “superorganism” to maintain a stable temperature.
Worker bees cluster tightly together and generate heat by isometrically contracting their flight muscles—a process known as shivering endothermy. This keeps the central brood nest within a narrow range of 33°C to 36°C.
Another significant task is processing the day’s collected nectar into honey. Nectar contains a high percentage of water, often up to 80%, which must be reduced to about 18% for stable storage. Bees accomplish this by fanning their wings throughout the night to create air currents within the hive, accelerating the evaporation of moisture from the nectar droplets. This continuous fanning also helps manage the colony’s humidity and carbon dioxide levels while ensuring the developing brood remains at the optimal temperature.