They can be identified by their distinctive markings, small size (similar to or slightly smaller or larger than a honey bee), their occurrence only in colonies, and a characteristic, rapid, side to side flight pattern prior to landing. All females are capable of stinging. Yellow jackets are important predators of pest insects.
A typical yellow jacket 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. Yellow jackets, 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. Yellow jackets 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. Yellow jackets have two antennae and two wings. These two wings are distinctive because they fold in half length-wise.
Due to their aggressive behavior, including stinging, many other insects exhibit mimicry of yellow jackets; in addition to numerous bees and wasps (Müllerian mimicry), the list includes some flies, moths, and beetles (Batesian mimicry).
Yellow jackets’ 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.