Yellow jackets (Vespula species) are social wasps often mistaken for bees due to their distinct black and yellow coloring. Unlike bees, yellow jackets are highly predatory and possess a varied diet that shifts dramatically throughout the season. They readily consume animal protein, which is mandatory for the colony’s survival. Yellow jackets are considered scavengers and predators, bringing them into frequent contact with human outdoor activities.
Protein: The Larval Diet
The yellow jacket’s need for protein is driven by the developing larvae during the spring and summer months. Adult worker wasps actively hunt and kill a wide range of arthropods, including caterpillars, flies, and spiders, to provide this nourishment. They also scavenge for animal protein from carrion, fish, and human food sources like deli meats and barbecue scraps.
The adult yellow jacket workers cannot ingest protein due to a constriction between their thorax and abdomen. Instead, they chew the protein into a soft, digestible slurry which they then feed directly to the larvae. In return for this protein meal, the larvae secrete a sugary, carbohydrate-rich liquid that the adult workers consume. This mutual exchange of food between the adults and the developing young is a specialized behavior known as trophallaxis.
The aggressive pursuit of meat and other animal products makes yellow jackets a nuisance around outdoor meals during the early and mid-summer. This behavior is a direct reflection of the large, rapidly growing colony’s demand for protein to fuel larval development. As long as the colony is expanding and producing brood, the adult workers are motivated to forage for protein to sustain this cycle.
Carbohydrates: The Adult Energy Source
The nutritional requirements for adult yellow jackets are primarily energy-based, fueled by carbohydrates. For most of the season, the adults receive the majority of their sugar from the larvae via the trophallaxis process. This sugary secretion provides the quick energy needed for the adults’ high-intensity activities, such as foraging and nest defense.
A significant shift occurs in late summer and early autumn when the queen stops laying eggs and the larval population begins to mature and decline. As the number of larvae decreases, the adult workers lose their internal source of sugar from the nest. This loss forces the large, late-season worker population to seek out external sources of pure carbohydrates to maintain their energy levels.
Consequently, the foraging behavior of yellow jackets changes from seeking protein to seeking accessible sugars. They become highly attracted to sources such as:
- Spilled sweet beverages
- Ripe or decaying fruit
- Nectar
- Soda
- Uncovered garbage
This seasonal transition explains why yellow jackets appear more numerous and aggressive around picnics and outdoor drinks as the summer draws to a close.
Practical Steps for Deterrence
Effective yellow jacket deterrence relies on disrupting their access to both protein and sugar sources based on the time of year. During the spring and early summer, when workers are focused on protein for the larvae, quickly clean up any meat or fish scraps and ensure outdoor garbage cans containing animal products are tightly sealed. Feeding pets outdoors should be avoided, or food bowls should be removed immediately after use.
As the season progresses into late summer, the focus must shift to eliminating carbohydrate attractants. Immediately clean up any spills of sugary drinks or juices, and use covered containers with a straw when consuming sweet beverages outdoors. Removing fallen, overripe fruit from gardens and orchards promptly can also significantly reduce foraging activity.
Trapping strategies can also be adjusted to match the seasonal diet. Early in the season, traps baited with protein, such as a small piece of meat or fish, are more effective at attracting workers. Later in the season, the same traps should be switched to a sugar-based bait, such as fruit juice or syrup, to target the carbohydrate-seeking adults.