Hornets are large social wasps belonging to the genus Vespa, distinguished by their size and coloration, often black or brown with yellow or orange markings. These insects live in organized colonies with a queen, workers, and drones. Their activity levels fluctuate significantly throughout daily and seasonal cycles, influenced by environmental factors that dictate their foraging, nesting, and reproductive behaviors.
Daily Activity Cycles
Hornets are primarily active during daylight hours, engaging in foraging and nest maintenance. During the morning and early afternoon, when temperatures are moderate, hornets are busy gathering resources. Activity increases around noon, correlating with higher ultraviolet B (UVB) radiation and temperature.
Though primarily diurnal, some hornet species, like the European hornet (Vespa crabro), are active at night, particularly around artificial light sources. This nocturnal behavior links to predatory habits, as more insect prey (e.g., moths) may be available after dark. Hornets become less active as temperatures drop and visibility decreases at night, often retreating to their nests; early morning hours before sunrise show reduced activity, with hornets typically inside their nests.
Seasonal Activity Patterns
Hornet activity follows a distinct seasonal pattern, dictated by their annual life cycle. In winter, hornets are at their least active. Most of the colony, including workers, males, and the old queen, die off as temperatures drop. Only newly fertilized queens survive winter by entering dormancy (diapause) in sheltered locations like under tree bark, in rotting logs, or within wall cavities.
As spring arrives, when temperatures consistently rise above 10°C (50°F), the overwintered queen emerges from dormancy. She builds a new nest from chewed wood pulp and saliva, laying the first eggs. Initially, colony growth is slow, with the queen nurturing the first worker brood. Once these workers mature, they take over nest expansion, foraging, and caring for offspring, leading to a gradual increase in activity.
Summer marks the peak of hornet activity, when colonies reach their largest size. Warm temperatures and abundant food fuel rapid colony growth, with nests housing hundreds to thousands of individuals. Workers forage for protein to feed larvae and carbohydrates for adult energy.
In late summer and early autumn, activity declines as the colony’s focus shifts. The queen stops producing worker eggs and lays eggs that develop into new queens and males. After mating, males die, and newly fertilized queens seek overwintering sites. Remaining workers and the old queen perish with colder weather.
Environmental Influences on Activity
Temperature impacts hornet activity, causing reduced movement or dormancy in cold conditions. As cold-blooded insects, their body temperature is influenced by surroundings. When temperatures drop below 7°C (45°F), hornets become less active; prolonged exposure below this threshold can be lethal. Conversely, extreme heat over 45°C (113°F) can be detrimental, causing hornets to seek shade or shelter.
Light levels also influence hornet behavior. While some hornet species can navigate and forage in low light, darkness reduces their activity, prompting them to return to the nest. Artificial lights can disorient hornets, causing them to hover around light sources, particularly at dusk or night.
Food availability influences hornet activity, particularly later in the season. As natural food sources like insects and nectar become scarcer in late autumn, hornets broaden their foraging range and may become more noticeable around human food sources. This scarcity contributes to colony decline as winter approaches. Adverse weather, such as heavy rain or strong winds, can temporarily reduce outdoor hornet activity, forcing them to remain within their nests.