European hornets (Vespa crabro) are the largest social wasp species native to Europe, now also established across North America after their introduction as early as 1840. They construct intricate paper-like nests from chewed plant materials and fibers, often in hollow trees or sheltered cavities. Unlike some other social insects, European hornet colonies operate on an annual cycle, naturally dying off each year due to environmental and biological factors.
The Annual Life Cycle of European Hornets
The life cycle of a European hornet colony begins in the spring when a single fertilized queen emerges from hibernation. She seeks a warm, dry, and undisturbed location, such as a hollow tree or an attic, to start building a new nest. The queen constructs initial paper cells and lays her first batch of eggs, which develop into sterile female worker hornets.
Once these first workers emerge, they take over nest construction, foraging for food, and tending to subsequent larvae, allowing the queen to focus solely on egg laying. Throughout the summer, the colony expands, adding more combs to the nest as the population grows.
By late summer or early autumn, the queen shifts her production from workers to reproductive individuals: new queens and males (drones). These new queens and males leave the nest to mate. After mating, the males typically die, and the newly fertilized queens seek out sheltered locations to hibernate through the colder months. The original queen, worker hornets, and males do not survive the approaching winter.
Factors Causing Colony Decline
Several factors contribute to the natural decline and death of European hornet colonies each year. As autumn progresses, decreasing ambient temperature is a significant environmental factor. European hornets, like other cold-blooded insects, become less active and their metabolism slows as temperatures drop, eventually becoming lethal to most colony members.
The availability of food sources also diminishes in cooler weather. Insect prey, a primary food for hornets, becomes scarce, and sources of sugary foods like fallen fruit and tree sap decline. This reduction in sustenance leads to starvation for many workers and larvae, further weakening the colony.
The original queen’s natural lifespan also plays a role; her egg-laying capacity declines, and she eventually perishes due to old age or exhaustion. Without the queen to produce new generations, the colony’s workforce cannot be replenished. Only the newly fertilized queens from the late summer brood can overwinter, ensuring the species’ survival into the next spring.
When European Hornet Colonies Die Off
The process of colony decline for European hornets typically commences in late autumn. This period is often marked by the first consistent cold snaps or hard frosts, which trigger the colony’s eventual demise. Workers, particularly susceptible to cold, become progressively less active and begin to perish.
While some nests in warmer, insulated spaces like attics might persist slightly longer, most European hornet colonies are largely inactive or lifeless by early winter, often around Christmas. By this time, the original queen, worker hornets, and male drones have succumbed to the changing conditions.
The precise timing can vary depending on the geographical location and the severity of winter’s onset. However, the annual pattern remains consistent: the colony does not survive beyond winter. Only newly mated queens find sheltered spots to hibernate and emerge the following spring to establish new colonies.
Signs of a Dying Colony
Observing a European hornet colony in its final stages reveals several indicators. A noticeable reduction in activity around the nest entrance is common. Fewer hornets will be seen foraging or flying, signaling a decrease in the colony’s overall population and vigor.
Individual hornets may exhibit sluggish or disoriented behavior. This is often a direct result of colder temperatures and a lack of energy due to food scarcity, making them slow to react and less agile. They might be seen moving slowly on surfaces or struggling to fly.
As the decline progresses, foraging activity eventually ceases, and the remaining hornets perish either inside or near the nest. The nest itself will not be reused by new queens the following year; it becomes an empty, abandoned structure.