Western Yellowjacket (Vespula pensylvanica)
This yellowjacket is a major pest species in California. It is primarily a scavenger and in the summer months adults are common around garbage receptacles in picnic and barbeque areas. Nests are usually constructed in abandoned rodent burrows or in house walls and attics. Nests contain 500 to 5,000 workers and start to decline in late September to October.
Common Yellowjacket (Vespula vulgaris)
The common yellowjacket can be a pest because adults are attracted to protein or sugar sources. This species is also considered a beneficial organism because workers prey on caterpillars and other insects. Nests are mostly underground but can be constructed inside house walls or in aerial locations. Nests are large containing 500 to 5,000 workers and remain active as late as December.
German Yellowjackets (Vespula germanica)
This yellowjacket is not a species native to California, but has become established in some areas. Adults are scavengers and predators of other insects. They build nests in hollow walls, attics and sometimes in aerial locations. Nests constructed inside walls can cause damage to the interior of a home and can result in adult yellowjackets inside the house. Nests contain 500 to 5,000 workers and start to decline sometime between late September and December.
Aerial Yellowjackets (Dolichovespula Spp.)
Aerial yellowjackets, make their paper nests in branches of trees, bushes, house eaves, or other places in the open air. They are considered beneficial because they only feed on insects. They can help control flies and other harmful insects like caterpillars and aphids. They can sometimes be confused with paper wasps, which are a less annoying species.
Bald or White-faced Hornet (Dolichovespula maculata)
The white-faced hornet is a large wasp and is widespread throughout North America. It is black and white in color. They usually build their nests in trees or shrubs. By the end of the summer these nests can be very large. The adults are much larger than yellowjackets and have whitish markings.