**Northwestern Yellowjackets** (*Vespula* species common to the Northwest, such as *Vespula pensylvanica*) are highly aggressive, social wasps known for establishing large colonies and defending their nests fiercely with painful stings. They are a significant **nuisance and stinging hazard** in the late summer and fall, when colonies are mature and workers shift their diet from insect protein to scavenging for sugars (soda, fruit, picnic foods). The conflict is their highly defensive behavior and the risk of anaphylaxis from multiple stings.
Taxonomy and Classification
Yellowjackets belong to the order Hymenoptera. They are social insects, with a single queen starting an annual colony in the spring. The workers are predatory in the early season (beneficial), but switch to aggressively scavenging human food in late summer. Unlike bees, yellowjackets can **sting repeatedly** and deliver a painful venom.
Physical Description
Adult Yellowjacket workers are 1/2 to 3/4 inch long.
- **Appearance (Key ID):** Sleek, black and bright yellow markings; narrow “waist” (petiole); hold their wings flat against their body when resting. Often confused with the beneficial paper wasp.
- **Nesting (Key ID):** The nests are made of chewed paper pulp, typically spherical, and located **underground** (in old rodent burrows), in wall voids, or inside dense, dark spaces (attics, sheds).
- **Conflict:** Severe stinging hazard and aggressive food/drink scavenging.
Distribution and Habitat
Northwestern Yellowjackets are widespread in the Pacific Northwest of the U.S. and Canada. Their habitat includes open meadows, forests, and heavily urbanized areas, where they establish colonies that can reach thousands of workers.
Behavior and Conflict
The conflict is defensive attacks and outdoor resource invasion.
- **Aggressive Defense:** Yellowjackets are quick to attack and sting when they perceive a threat to their nest or food source. They often mark the target with a chemical that signals other wasps to join the attack.
- **Stinging Hazard:** Yellowjackets are responsible for a majority of insect-related emergency room visits, primarily due to severe allergic reactions (anaphylaxis).
- **Scavenging:** They are highly attracted to open sodas, beer cans, fruit, meat, and pet food, often crawling into containers undetected.
Management and Prevention
Control requires professional nest elimination and sanitation.
- **Do NOT attempt to seal the entrance** (this drives them into the structure).
- **Professional Service:** Due to the risk of aggressive mass attack, nest elimination (especially underground or in walls) should be done by a pest control professional using specialized dusts or liquid non-repellent insecticides.
- Keep all food, soda cans, and garbage containers sealed outdoors.
- Use sweet-baited traps (protein in early season, sugar in late season) placed **away** from the activity area to divert foraging workers.
Conservation and Research
Northwestern Yellowjackets are managed as high-priority public safety and nuisance pests. Research focuses on improving baiting and trapping strategies for large-scale control, especially in public parks, and developing effective non-toxic deterrents for outdoor dining areas.