From this time until her death in the autumn, the queen remains inside the nest laying eggs. The colony then expands rapidly reaching a maximum size of 4,000 and 5,000 workers and a nest of 10,000 and 15,000 cells in late summer. At peak size, reproductive cells are built with new males and queens produced. Adult reproductives remain in the nest fed by the workers. New queens build up fat reserves to over winter. Adult reproductives leave the parent colony to mate. After mating, males quickly die while fertilized queens seek protected places to over winter. Parent colony workers dwindle, usually leaving the nest and die, as does the foundress queen. Abandoned nests rapidly decompose and disintegrate during the winter but can persist as long as they are kept dry but are rarely used again.

In the spring, the cycle is repeated. (Weather in the spring is the most important factor in colony establishment.) Although adults feed primarily on items rich in sugars and carbohydrates (fruits, flower nectar and tree sap), the larvae feed on proteins (insects, meats, fish, etc.). Adult workers chew and condition the meat fed to the larvae. Larvae in return secrete a sugar material relished by the adults, an exchange of material known as trophallaxis.

Although they lack the pollen-carrying structures of bees, yellowjackets can be minor pollinators when visiting .