Yellow jackets, like some species of bees, ant wasps, and termites, live in colonies where many workers serve a single egg-laying queen. The colonies begin to form in early spring, when fertile females emerge from the sheltered locations where they spent the winter and search for nest sites. At first the nest is just a spherical shell the size of a golf ball enclosing a honeycomb structure where the female lays five or six eggs. The eggs hatch into larvae, which the mother then nourishes with regurgitated insects. When the larvae turn into adults, they assume all the work roles: foraging, feeding larvae, enlarging the nest, and defending the nest. The female that started the colony—the queen—never leaves the nest again. Its only responsibility now is to produce more eggs. Through the spring and summer, the colony grows.
The nest is enlarged as the workers add tiers to the honeycomb-like brood chambers. The outer shell is built up, too, and by mid-summer the nest resembles a gray paper volleyball (some nests reach basketball-sized proportions). These nests can become quite conspicuous, hanging from trees or suspended from the eves of buildings. As for the species that nest underground, their homes usually begin in abandoned rodent burrows that are further excavated as the nest grows. The nest structure, though, is the same as those above ground.
Once the nest reaches full size, the queen starts to lay the eggs that develop into the males and females that will leave the colony, mate, and begin the cycle again the following year. All the workers and the year-old queen, meanwhile, will die. It’s during this time, middle to late summer, that the workers get defensive. They’re focused on protecting the new males and virgin queens within, for these represent the total reproductive output of the colony. It’s also during this time that we have most of our interactions with yellow jackets.
Many species begin to forage on carrion to feed the growing larvae, and this brings them to our outdoor meals. But even yellow jackets at picnic tables are unlikely to sting people unless they’re physically threatened. Their aggressive behavior is reserved mostly for defending the nest. Thus if a walkway near your house takes you close to a hanging nest or an underground nest entrance, you may be attacked for passing too close or for lingering too long in a certain spot. A nest that was not previously a cause for concern becomes a menace when the yellow jackets change their zone of tolerance.