Yellow jackets (Vespula genus) are common social wasps frequently encountered in outdoor environments. They are often mistaken for bees due to their distinct yellow and black banding patterns. While known as aggressive picnic pests, they are highly organized social insects that fulfill a significant ecological role. Their foraging habits change throughout the year, driven by the nutritional needs of their growing colony.
Yellow Jackets as Predators
Yellow jackets are accomplished predators, and they certainly include flies in their diet. Worker yellow jackets actively hunt a variety of small arthropods, including house flies, blow flies, caterpillars, and spiders. This predatory behavior is concentrated during spring and summer when the colony requires protein for its developing young.
The worker uses its powerful mandibles to capture and subdue prey. Once killed, the worker dismembers the insect and chews the protein into a pulp, which is transported back to the nest for the larvae. This hunting activity makes yellow jackets valuable biological control agents in many ecosystems.
The Broader Diet of Yellow Jackets
The yellow jacket colony’s diet consists of two distinct nutritional categories: protein for the larvae and carbohydrates for the adult workers. Protein sources are diverse, including live prey, various insects, and scavenging on carrion or meat scraps from human food waste.
Carbohydrates provide the energy required for the adults’ constant flight and foraging. These sugary liquids include flower nectar, tree sap, and honeydew secreted by aphids. Later in the season, when natural sources become scarce, adult workers are attracted to ripe or decaying fruits, fruit juices, and sugary drinks. This opportunistic feeding sustains the colony throughout the warmer months.
Why Yellow Jackets Hunt and Forage
The primary motivation for a worker’s foraging behavior is maintaining the colony’s lifecycle. Adult worker wasps cannot digest solid protein due to a constriction in their digestive system. They rely almost entirely on easily absorbed sugars for fuel, hunting protein strictly to feed the developing larvae inside the nest cells.
A unique nutritional exchange, called trophallaxis, occurs at the nest. The larvae consume the protein provided by the workers and, in return, secrete a sugar-rich fluid. Adult workers consume this secretion, which serves as their main energy source throughout the summer. This symbiotic relationship explains the seasonal shift in behavior. As the queen’s egg-laying slows and the number of larvae decreases in late summer, workers lose their internal sugar source. They then become aggressive scavengers, seeking external carbohydrate sources until the colony declines in the fall.