The most common paper wasps in California are the apches paper wasp (Polistes apachus), the northern paper wasp (Polistes fuscatus) and the European paper wasp (Polistes dominula). Paper wasps build open, umbrella-shaped nests, often found suspended from eaves or window casings on the outside of your home. They also like to build their nests in orchards and vineyards under the branches of trees. They occasionally build nests in attics. Paper wasps build their nests by scraping and chewing wood collected from fences, tree bark, plant stems and old, weathered buildings. The finished nests is usually umbrella-shaped. Each cell in the nest contains an egg, which hatches into a larvae. The larvae are fed caterpillars.
Paper wasp nests are relatively small, usually consisting of less than 200 individuals. They are not particularly aggressive, but will defend their nests and can deliver a painful sting.
There are five species of yellowjackets that are common in urban areas of California. The most commonly encountered species are the western yellowjacket (Vespula pennsylvanica) and the common yellowjacket (Vespula vulgaris). The German yellowjacket (Vespula germanica) is becoming more common in urban areas and often moves into homes. Two species that build aerial nests in trees are the aerial yellowjacket (Dolichovespula arenaria) and the bald-faced hornet (Dolichovespula maculata), which is actually a yellowjacket. The western, common and German yellowjackets frequently nest in the ground, often in rodent burrows, but will also build nests in the walls and attics of houses. Yellowjacket colonies can range between 1,500 and 15,000 individuals, depending on the species. The bald-faced hornets have smaller colonies, usually consisting of 100 to 400 individuals.
Yellowjackets are black and yellow in color except for the baldfaced hornet which has a black abdomen and a black face with white markings. It is also a little larger than the other yellowjackets. Yellowjacket workers usually only live a year but occasionally can survive several years and become quite large.
Generally yellowjackets can be considered beneficial as they kill a lot of flies, beetle larvae, caterpillars and other insect pests. However, when they are in or near a home, then can be dangerous to people and pets. They are attracted to a variety of foods people eat and drink, particularly sweets and protein foods. They love BBQs. They are considered venomous, stinging social insect, that are abundant in urban areas; when nests are disturbed, defending worker wasps can inflict multiple stings; foraging worker wasps may be a nuisance at picnics and other outdoor events.