A typical yellowjacket worker is about 12 mm (0.5 inches) long, with alternating bands on the abdomen while the queen is larger, about 19 mm (0.75 inches) long (the different patterns on the abdomen help separate various species). Workers are sometimes confused with honey bees, especially when flying in and out of their nests. Yellowjackets, in contrast to honey bees, are not covered with tan-brown dense hair on their bodies and lack the flattened hairy hind legs used to carry pollen. Yellowjackets have a lance-like stinger with small barbs and typically sting repeatedly, though occasionally the sting becomes lodged and pulls free of the wasp's body; the venom, like most bee/wasp venoms, is primarily only dangerous to those who are allergic, unless a victim receives a large number of stings (main article: Bee sting). All species have yellow or white on the face. Mouthparts are well-developed for capturing and chewing insects, with a proboscis for sucking nectar, fruit and other juices. Nests are built in trees, shrubs or in protected places such as inside human-made structures (attics, hollow walls or flooring, in sheds, under porches and eaves of houses), or in soil cavities, mouse burrows, etc. Nests are made from wood fiber chewed into a paper-like pulp.
Due to their aggressive behavior, including stinging, many other insects exhibit mimicry of yellowjackets; in addition to numerous bees and wasps (Müllerian mimicry), the list includes some flies, moths, and beetles (Batesian mimicry).
Yellowjackets' closest relatives, the hornets, closely resemble them but have a much bigger head, seen especially in the large distance from the eyes to the back of the head.
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 overwinter. Adult reproductives leave the parent colony to mate. After mating, males quickly die while fertilized queens seek protected places to overwinter. 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. In late summer, foraging workers (nuisance scavengers) change their food preference from meats to ripe, decaying fruits or scavenge human garbage, sodas, picnics, etc., since larvae in the nest fail to meet requirements as a source of sugar.
Although they lack the pollen-carrying structures of bees, yellowjackets can be minor pollinators when visiting .
Yellowjacket nests usually last for only one season, dying off in winter. The nest is started by a single queen, called the foundress. The nest typically can reach the size of a basketball by the end of the season. In parts of Australia, New Zealand, the Pacific Islands and southwestern coastal areas of the United States, the winters are mild enough to allow nest overwintering. Nests that survive multiple seasons become massive and often possess multiple egg-laying queens.
In the Southeastern United States, where southern yellowjacket (Vespula squamosa) nests may persist through the winter, colony sizes of this species may reach 100,000 adult wasps.
The yellowjacket's most visible place in American culture is as the mascot of the University of Rochester, Georgia Institute of Technology, and Baldwin-Wallace College. The NHL franchise of Columbus, Ohio, the Columbus Blue Jackets, formerly used a secondary logo featuring a "blue jacket" insect, based on the yellowjacket. This fictional "blue jacket" resembles a yellowjacket wearing a blue Civil War uniform.
In cartoons and some artwork, bees are usually drawn as yellowjackets.