Most Yellowjacket species are smaller than paper wasps (1/2 to 3/4 inches) but are more stocky in appearance. Most of these are black-and-yellow; some are black-and-white (such as the bald-faced hornet, Dolichovespula maculata), while others may have the abdomen background color red instead of black. 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.
They also build nests much larger than their paper wasp relatives. Their nests consist of several combs surrounded by paper envelopes and resemble a paper-m ch ball. Most yellowjackets build nests in underground or enclosed sites such as wall voids, attics, and inside hollow logs. However, a few species, such as the baldfaced hornet, build their nests in trees and shrubs or on buildings. The population in mature colonies can be quite large, ranging from 200 to 700 adults in the baldfaced hornet colonies to 1,000 to 5,000 adults in the southern and eastern yellowjacket colonies.
Due to their large colony size and defensive nature,yellow-jackets are more aggressive than paper wasps. Yellowjackets have effective means of defending their colonies. They often have “guards” at their nest entrances, and the colony can easily be disturbed by rapid movement and vibrations near the nest. For this reason, one will almost certainly be stung if a lawn mower or trimmer is used near a yellowjacket nest. In some species, an alarm chemical is released upon stinging that causes nest mates to join the attack.