Yellowjacket venom contains a pheromone that encourages other yellowjackets to attack.
The chemical tag marks the victim as a threat and makes him or her a potential target for other yellowjackets. Unfortunately, pretty much anything can make yellowjackets mad, such as walking near their nests or mowing the lawn over their colonies.
- https://www.mentalfloss.com/animals/insects/wasp-facts
