Yellowjackets are social wasps belonging to the genera Vespula and Dolichovespula. They are identified by their bright yellow and black banded markings, a pattern known as aposematism that warns of their defensive capabilities. Unlike bees, yellowjackets have a smooth, shiny body and a noticeably thinner waist. Their tendency to build large, annual colonies and scavenge human food sources in late summer often leads to their reputation as bothersome pests.
The Annual Life Cycle and Colony Structure
The yellowjacket colony life cycle is seasonal, beginning with a single, fertilized queen that has successfully overwintered. Emerging from sheltered spots like hollow logs or wall voids, the queen selects a nesting site and constructs a small paper nest by chewing wood fibers. She lays her first batch of eggs in the cells and, until they mature, she must forage and defend the fledgling nest alone.
Once the first generation of offspring emerges as sterile female workers, the queen remains inside the nest for the rest of her life, focusing solely on egg-laying. The workers take over all other colony duties, including nest expansion, temperature regulation, and foraging. The colony expands rapidly throughout the summer, often reaching 4,000 to 5,000 workers and a nest size of up to 15,000 cells by late August or September.
In the late summer and fall, the workers construct larger cells where the queen lays eggs that develop into new, fertile queens and males. The young queens and males leave the parent colony to mate, and the males die shortly thereafter. The newly fertilized queens seek out protected places to hibernate, while the remaining workers, the original queen, and the entire colony perish with the onset of cold weather.
Predation and Scavenging
Yellowjackets are generalist feeders, and their diet shifts dramatically as the colony progresses through the season. In the spring and early summer, workers focus heavily on predation, hunting a variety of insects, spiders, and caterpillars. The workers chew and process this protein-rich prey before feeding it to the developing larvae inside the nest.
This predatory activity is beneficial for pest control, as a single colony can consume thousands of nuisance insects over a summer. In return for this protein, the larvae secrete a sugary substance that the adult workers consume, providing the adults with the carbohydrates they need for energy. This reciprocal feeding relationship, known as trophallaxis, is crucial for the colony’s early growth.
The most noticeable shift in yellowjacket behavior occurs in the late summer and early fall when the larval population matures and the demand for protein drops significantly. The adult workers, still requiring a high-energy diet, switch their focus to scavenging for sugars and carbohydrates. They become persistent visitors at picnics and outdoor dining areas, seeking out sweet drinks, ripe fruit, and sugary human foods.
This dietary transition from active predation to opportunistic scavenging explains why yellowjackets seem more abundant and bothersome to humans in the fall. They also scavenge meat and carrion throughout the season, but their attraction to human-associated sweets brings them into frequent conflict with people. Their opportunistic nature means they exploit any available food source to sustain themselves.
Defensive Behavior and Stinging
Yellowjackets are known for their aggressive nature, especially when they perceive a threat to their nest or a valuable food source. Their instinct to protect the colony is the primary motivation for stinging, and a perceived threat can trigger a defensive reaction. When disturbed, workers release an alarm pheromone, a chemical signal that quickly recruits other nearby yellowjackets to join the defense and attack.
A key difference between yellowjackets and honey bees is that yellowjackets possess a lance-like stinger without barbs, allowing them to sting repeatedly without tearing their abdomen or dying. This ability to sting multiple times makes them dangerous if a nest is accidentally disturbed. Their nests are often concealed, built underground in old rodent burrows, in tree cavities, or within structural voids like wall spaces.
To avoid provoking a yellowjacket, be aware of common nesting sites and avoid rapid movements, which they may interpret as a threat. If a yellowjacket lands nearby, swatting at it can be seen as an aggressive act and will likely trigger a defensive sting. Sealing trash cans and keeping food covered during outdoor activities minimizes the chances of attracting foraging workers.