Most wasps are active during the day, a common observation that often leads to questions about their whereabouts and activity once darkness falls. While it might seem that wasps disappear entirely at night, their behavior simply shifts from active foraging and nest building to a period of rest and recuperation. The reasons behind this change are primarily rooted in their biology and ecological adaptations.
The Primary Limitation: Wasp Vision at Night
The visual system of most wasps is optimized for daytime conditions, making night flight impractical. Wasps possess compound eyes, composed of numerous individual light-sensing units called ommatidia. These eyes excel at detecting movement and offer a wide field of view, but their design limits effectiveness in low-light environments. Each ommatidium functions best with ample light, making them unsuited for gathering limited photons after sunset.
In addition to compound eyes, wasps also have three simple eyes, called ocelli. These ocelli are highly sensitive to light and assist with flight stability and detecting changes in light intensity. While more light-sensitive than compound eyes, ocelli primarily act as light sensors rather than providing detailed vision. Most wasps lack specialized adaptations, such as large ocelli or superposition eyes, found in truly nocturnal insects for efficient vision in darkness.
More Than Just Sight: Other Factors Limiting Night Activity
Beyond visual limitations, several other factors contribute to why most wasps do not fly at night. Flight is an energy-intensive activity, requiring significant metabolic resources. Resting during cooler, darker hours allows wasps to conserve energy, crucial for demanding daytime tasks like foraging for food and constructing nests.
Navigation also becomes significantly more challenging without daylight. Many diurnal insects, including wasps, rely on visual cues such as the sun’s position or polarized light patterns in the sky for orientation. These cues are absent at night, making it difficult for wasps to navigate effectively and find their way back to their nests.
The nocturnal environment introduces an increased risk from predators. Many animals, such as bats, raccoons, and certain birds, are active at night and prey on insects, making wasps more vulnerable if they were to fly after dark. The availability of food sources also changes dramatically at night. Many flowers close at dusk, and the prey insects that wasps hunt are typically less active, reducing foraging opportunities.
The Rare Exception: Wasps That Fly After Dark
While most wasps are strictly diurnal, some species have adapted to be active during twilight (crepuscular) or even fully nocturnal. European hornets (Vespa crabro) are a notable example; they are known to fly in dim light conditions and can be active after dark, especially when attracted to artificial lights. They can fly in light levels significantly lower than common wasps.
Other nocturnal or crepuscular wasps include certain parasitic wasps, which may be attracted to lights while searching for hosts. Some Apoica wasps are truly nocturnal and possess adaptations in their ocelli that aid in night foraging. Certain tropical paper wasps and nocturnal spider wasps also exhibit nighttime activity. These species demonstrate that nocturnal flight in wasps is possible when specific ecological pressures drive the evolution of necessary adaptations.
Where Wasps Go When Night Falls
When night falls, most wasps return to their nests or seek sheltered locations to rest. For social wasps, this typically means retreating into their paper nests, which offer protection from the elements and nocturnal predators. Inside the nest, wasps enter a period of reduced activity or dormancy, continuing with internal nest duties like tending to larvae or repairing the nest.
Solitary wasps and some social wasps may find refuge under leaves, in tree crevices, or within other protected spots away from their main nest. This period of inactivity serves several purposes: it conserves energy, protects them from cooler nighttime temperatures, and reduces their exposure to nocturnal threats. Wasps remain alert to potential disturbances even during these resting periods and can react quickly if their shelter or nest is threatened.