Yellowjackets are extremely aggressive and will attack if their nest is threatened. When stung, an intruder is marked with a special scent that encourages other yellow jackets to attack. As with fire ants, some people can have severe reactions to yellow jacket stings. These insects are actually beneficial because they prey on many insect pests such as flies and caterpillars.
The nest is usually built underground and resembles a paper football. The fertile queen lays eggs in a small hole in spring and the hole is excavated by newly-hatched workers as the summer progresses. The underground nest resembles that of the paper wasps which hang from porch roofs.
Nests are initially quite small but can contain over 5,000 yellow jackets in the fall. Yellow jacket nests are abandoned in the late fall and are never reused.
Yellow jackets that you see hovering over food or water are scavengers from the nest and usually pose no problem unless provoked. The greatest danger occurs when humans come too close to the nest, which often goes unnoticed until the yellow jackets swarm out to attack.
Insecticide treatment of nests should only be done in the late evening or night when all the yellow jackets are resting in the nest and are not as aggressive as during daylight hours. If a nest is in a spot where people frequent, it should probably be destroyed.
The safest way is to spray the nest opening with an aerosol “Wasp and Hornet” spray (click for sources) after dusk. If activity is observed the next day, repeat the application. Sevin dust (click for sources) can be dropped into the nest entrance if you can run by fast enough. Complete kill of the nest is usually achieved within 24 hours.
yellowjacket entrance hole
yellowjacket nest found in bale of pinestraw