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Yellow jacket is the common name in North America for predatory wasps of the genera Vespula and Dolichovespula. Members of these genera are known simply as a wasp in other English-speaking countries. 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 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 which can cause pain to the person who has been stung. Yellow jackets are important predators of pest insects.

Yellow Jacket Identification
Face of a southern yellow jacket (Vespula squamosa)

Yellow jackets have sometimes been mistakenly called but they are actually in the wasp classification. A typical yellow jacket worker is about 12 mm (0.5 in) long, with alternating bands on the abdomen while the queen is larger, about 19 mm (0.75 in) 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. They have a lance-like stinger with small barbs and typically sting repeatedly, though occasionally the stinger becomes lodged and pulls free of the wasps 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. All species have yellow or white on the face. Mouthparts are well-developed with strong mandibles 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 yellow jackets; in addition to numerous bees and wasps, 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.

Yellow Jacket Life Cycle & Habits
A Vespula squamosa queen

Yellow jackets are social hunters living in colonies containing workers, queens, and males. Colonies are annual with only inseminated queens overwintering. Fertilized queens occur in protected places such as hollow logs, in stumps, under bark, in leaf litter, in soil cavities, and human-made structures. Queens emerge during the warm days of late spring or early summer, select a nest site, and build a small paper nest in which eggs are laid. After eggs hatch from the 30 to 50 brood cells, the queen feeds the young larvae for about 18 to 20 days. After that, the workers in the colony will take over caring for the larvae, feeding them with chewed up food, meat or fruit. This act is called trophallaxis. Larvae pupate, emerging later as small, infertile females called workers. By mid-summer, the first adult workers emerge and assume the tasks of nest expansion, foraging for food, care of the queen and larvae, and colony defense.

From this time until her death in the autumn, the queen remains inside the nest, laying eggs. The yellow jacket 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 to die, as does the foundress queen. Abandoned nests rapidly decompose and disintegrate during the winter. They 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. This exchange is known as trophallaxis. In late summer, foraging workers 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. This is why yellowjackets are known largely as an unwelcome nuisance at picnics. Although they lack the pollen-carrying structures of bees, yellowjackets can be minor pollinators when visiting flowers.

Notable species
* European yellow jackets (the German wasp, Vespula germanica and the common wasp, Vespula vulgaris) were originally native to Europe, but are now established in North America, southern Africa, New Zealand, and eastern Australia.
* The eastern yellow jacket (Vespula maculifrons), and western yellow jacket (Vespula pensylvanica), are native to North America.
* The southern yellow jacket, Vespula squamosa
* Bald-faced hornets, Dolichovespula maculata, belong among the yellow jackets rather than the true hornets, but are not usually called yellow jackets because of their ivory-on-black coloration.
* Tree wasp, Dolichovespula sylvestris

Two-year yellowjacket nest

Yellow Jacket Nest
Dolichovespula species (for example, the aerial yellow jacket, Dolichovespula arenaria, and the bald-faced hornet, Dolichovespula maculata) tend to create exposed aerial nests.

Vespula species, in contrast, build concealed nests, usually underground.

Yellow jacket nests usually last for only one season, dying off in winter.Typically, a nest can reach the size of a basketball by the end of a 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.

United States Yellow Jackets

In 1975, the German yellow jacket first appeared in Ohio, and has now become the dominant species over the eastern yellow jacket. It is bold and aggressive, and if provoked, it can sting repeatedly and painfully. It will mark aggressors, and will pursue them if provoked. The German yellow jacket builds its nests in cavities (not necessarily underground) with the peak worker population in temperate areas between 1,000 and 3,000 individuals between May to August, each colony producing several thousand new reproductive after this point, through November. The eastern yellowjacket builds its nests underground, also with the peak worker population between 1,000 and 3,000 individuals similar to the German yellow jacket. Nests are built entirely of wood fiber (usually weathered or dead) and are completely enclosed (football or soccer-ball shaped) except for a small opening (entrance) at the bottom. The color of the paper is highly dependent on the source of the wood fibers used. The nests contain multiple, horizontal tiers of combs (10 or more) within. Larvae hang down in combs.

In the southeastern United States, where southern yellow jacket (Vespula squamosa) nests may persist through the winter, colony sizes of this species may reach 100,000 adult wasps.[citation needed] The same kind of nest expansion has occurred in Hawaii with the invasive western yellow jacket Vespula pensylvanica.