Bees are winged insects, widely recognized for their role as pollinators. While most of the over 20,000 known species are active during the day, a fascinating subset defies this expectation. These unique bees emerge and work under the cover of darkness, challenging the common perception of these insects as exclusively diurnal.
Identifying Bees Active at Night
While most bee species are diurnal, a small percentage are either truly nocturnal or crepuscular, active during twilight hours. Around 250 bee species exhibit some form of nighttime activity. This behavior has evolved independently in at least four of the seven bee families: Andrenidae, Apidae, Colletidae, and Halictidae, indicating it is a specialized adaptation that arose multiple times.
Some of the most studied nocturnal bees belong to the Halictidae family, commonly known as sweat bees. The genus Megalopta, found primarily in Neotropical regions, is well-known for its nocturnal species, such as Megalopta aeneicollis and Megalopta genalis. These bees often build nests in dead wood and can display social behavior. Other notable nocturnal genera include Ptiloglossa (Colletidae family) and some species within the Xylocopa (carpenter bee) genus. These specialized species have distinct characteristics, including larger eyes.
How Bees Navigate in Darkness
Nocturnal bees possess specialized sensory adaptations that enable them to function effectively in low-light conditions, primarily enhanced vision. Unlike their diurnal counterparts, nocturnal bees often have significantly enlarged ocelli, simple eyes on their heads adept at detecting changes in light intensity. Their compound eyes, composed of many individual light-gathering units called ommatidia, are also adapted to maximize light capture.
These visual enhancements allow nocturnal bees to navigate through their environment, locate night-blooming flowers, and successfully return to their nests when light is scarce. The ommatidia in their compound eyes are larger, providing a wider field of view and collecting more photons. While vision is a primary adaptation, nocturnal bees also utilize other sensory cues, such as olfaction. Strong scents emitted by many night-blooming flowers guide them to floral resources.
Why Some Bees Work After Sunset
The shift to nighttime activity provides several ecological advantages for these unique bee species. One significant reason is the reduction of competition for floral resources. By foraging after sunset, nocturnal bees exploit a different ecological niche, avoiding the vast majority of diurnal pollinators that are active during the day. This allows them to access nectar and pollen from flowers that specifically open or become most fragrant at night, such as moonflowers or night-blooming jasmine. These plants often rely exclusively on nocturnal visitors for pollination, forming a specialized relationship with these bees.
Operating under the cover of darkness can also offer protection from certain predators. Many birds and predatory insects that hunt bees are active during the day, so nocturnal activity can reduce exposure to these threats. Furthermore, in extremely hot climates, foraging at night can help bees regulate their body temperature more effectively. The cooler nighttime temperatures allow them to avoid the physiological stress of high daytime heat, which can be particularly beneficial in arid or tropical environments where many nocturnal bee species are found. This combination of reduced competition, access to unique floral resources, and predator avoidance contributes to the evolutionary success of nocturnal bees.