Yellow jackets are named after their black and yellow bodies, which are often confused with that of a bee. However, yellow jackets exhibit less hair than bees, a slimmer, more defined waist/abdomen, and lack the expanded hind legs bees use to carry pollen. Yellow jackets are typically black and yellow, with some occasionally being white and black. They measure between 10 and 16 mm in length with elongates wings on the same length, which fold laterally when not in use.
Yellow jacket nests are first constructed by the queen and reach about the size of a walnut before sterile female workers take over construction. The queen initially starts the nest by making a single layer or canopy and working outwards until she reaches the edges of the cavity. Beneath the canopy she constructs a stalk to which she can attach several cells; these cells are where the first eggs will be laid. The queen then continues to work outwards to the edges of the cavity after which she adds another tier. This process is repeated, each time adding a new tier until eventually enough female workers have been born and matured to take over construction of the nest leaving the queen to focus on reproduction. For this reason, the size of a nest is generally a good indicator of approximately how many female workers there are in the colony and some hornets’ nests eventually grow to the size of beach balls.
Social yellow jacket colonies often have populations of between three and ten thousand female workers at maturity, although a small proportion of nests are seen on a regular basis that are over three feet across and potentially contain upwards of twenty thousand workers and at least one queen. What has also been seen are nests close to one another at the beginning of the year growing quickly and merging with one another to create nests with tens of thousands of workers.