Diurnal refers to the behavior of animals that are primarily active during daylight hours. This pattern is common among most bees. While most bees are noticeable under the sun, a small number of bee species have adopted different schedules, venturing out when light is dim or absent. This article explores the reasons behind the daytime activity of most bees and highlights the exceptions.
Understanding Diurnal Bee Behavior
Most bee species, such as honey bees and bumblebees, exhibit a daily routine centered around daylight. These bees forage for nectar and pollen from flowering plants. Foraging begins with the rising sun, allowing them to gather resources throughout the day.
Bees rely heavily on sunlight for navigation. They possess an internal compass that uses the sun’s position to orient themselves and find their way back to the hive. Even on cloudy days, bees can detect patterns of polarized light in the sky, which helps them to determine the sun’s location and maintain their course. Honey bees, for instance, communicate the direction and distance of food sources to their nestmates through a complex “waggle dance,” which is oriented relative to the sun’s position.
Factors Influencing Bee Activity
Light availability plays a significant role in bee activity. Most bees have visual systems adapted for bright conditions, hindering navigation and flower location in low light. Sunlight provides visual cues for flight paths and communication.
Temperature also influences bee activity. Bees are ectothermic, meaning their body temperature is largely regulated by their environment. They require certain temperatures for efficient flight. Honey bees, for example, maintain stable thorax temperatures for flight within an air temperature range of approximately 19 to 37 degrees Celsius. Bumblebees, similarly, show optimal flight performance between 25 and 27 degrees Celsius, with activity declining at colder or significantly warmer temperatures.
Floral resource availability also aligns with diurnal patterns. The majority of flowering plants release nectar and pollen during the day, coinciding with peak sunlight and temperatures conducive to bee flight. This synchronization ensures that bees can access the food sources they need, while plants benefit from pollination when their floral rewards are most accessible.
Bees Active Beyond Daylight Hours
While most bees are diurnal, approximately 1% of described bee species, totaling around 250 species, exhibit activity beyond typical daylight hours. These bees are categorized as crepuscular, meaning they are active during dawn and dusk, or truly nocturnal. Examples include certain sweat bees in the genus Megalopta and some Lasioglossum species, as well as the Indian Carpenter bee, which is obligately nocturnal.
These bees have evolved specialized adaptations for low-light environments. Many crepuscular and nocturnal bees possess larger compound eyes and ocelli (simple eyes) compared to their diurnal counterparts, to gather limited light. Some can even perceive color in dim light, similar to human vision in twilight conditions.
The evolutionary reasons for these nighttime adaptations are varied. Foraging at dawn, dusk, or night allow access to specialized floral resources that only open or release scents during these periods. It also reduces competition with the more numerous diurnal bee species and potentially offer an escape from daytime predators or parasites. This temporal niche partitioning allows bee species to coexist by utilizing resources at different times.