Most bee and wasp species are known for their daytime activity, diligently foraging and building nests under the sun. While this diurnal pattern is common, some species have evolved to operate during darker hours. This article explores nocturnal and crepuscular bees and wasps, highlighting their unique behaviors and the environmental factors that influence their activity.
Bees: Daytime Fliers with Nocturnal Exceptions
The vast majority of bee species, approximately 99%, are diurnal, active exclusively during daylight hours. Common species like honeybees and bumblebees rely on sunlight for navigation and foraging. If caught out after dark, these bees can become disoriented and struggle to return to their hives. Despite this general trend, about 250 bee species globally have evolved to be active in low-light or darkness. These include truly nocturnal bees and crepuscular bees, active during twilight hours at dawn and dusk.
Nocturnal bees display remarkable adaptations to navigate and forage in dim environments. Many species, such as the Megalopta sweat bees in Central and South America, possess significantly larger compound eyes, making them up to 27 times more light-sensitive than their diurnal counterparts. Their simple eyes, ocelli, are also notably enlarged and play a crucial role in light detection; Megalopta genalis ocelli have an occupancy ratio five times greater. Some nocturnal bees, like the Indian Carpenter Bee (Xylocopa tranquebarica), can even forage in complete darkness, potentially utilizing neural adaptations. This nocturnal activity allows these bees to exploit niches with reduced competition for nectar and pollen from flowers that bloom only at night.
Wasps: Primarily Diurnal, Rare Nocturnal Activity
Like bees, most wasp species are primarily diurnal, conducting their foraging, nest building, and care for their young during daylight hours. They rely on warmer temperatures and light for their metabolic processes and activity. If temperatures drop at night, their activity levels typically decrease, and they often return to their nests. However, a few specialized wasp species exhibit nocturnal or crepuscular behaviors, though true nocturnal wasps are considerably less common than nocturnal bees.
The genus Provespa, sometimes called “night wasps” or “night hornets” in Southeast Asia, are the only truly nocturnal members of the Vespinae subfamily. The European Hornet (Vespa crabro) also demonstrates crepuscular activity, often flying at dusk or in the early evening, and can even forage at night. Some parasitic wasps, belonging to families like Ichneumonidae and Braconidae, are also known to be nocturnal. These wasps often target night-feeding insects, such as caterpillars, for laying their eggs. Wasps that display nocturnal activity often do so to access prey available only at night or to reduce competition with diurnal insects.
Environmental Factors and Behavioral Triggers
The ability of bees and wasps to fly at night is significantly influenced by environmental factors. Ambient light levels play a primary role; some nocturnal species thrive in starlight or moonlight, while others are limited by very dim conditions. Moonlight can be a crucial navigational aid. Artificial light sources can also impact insect behavior, sometimes confusing diurnal bees that mistake them for natural illumination or food sources, leading to disorientation.
Temperature is another important abiotic factor governing insect activity. Cooler nighttime temperatures generally reduce the activity of many bee and wasp species. However, some nocturnal species are adapted to these lower temperatures, allowing them to remain active.
The availability of resources also drives nocturnal activity; night-blooming flowers provide nectar and pollen for nocturnal bees, while the presence of nocturnal prey attracts specialized wasps. Wasps may be drawn to artificial lights indirectly because these lights attract other insects, which then become a food source. Blue and ultraviolet light from artificial sources have been shown to particularly interfere with the natural patterns of flying insects.