Summary of Yellowjackets of Napa County

Summary of Napa County Yellowjackets

Scientific Name	Common Name	Habitat/Ecology	Adult/Colony Activity Period
Dolichovespula arctica	N/A	Obligatory social parasite of Aerial Yellowjacket (Dolichovespula arenaria) and Dolichovespula norvegicoides colonies.	April - July
Dolichovespula arenaria	Aerial Yellowjacket	One of the most common wasps in North America. Nest construction begins in March with most colonies dying out by July. Nests are usually above ground ranging from a few inches up to the tops of trees. Colonies can also be found in or on man-made structures such as sheds, houses, garages, etc. The number of workers in an active colony at any one time can be as high as 700. Adults tend to be less aggressive than most other species of yellow jackets, although when aroused they have been known to spray venom out of the sting.	March - July
Dolichovespula maculata	Bald-Faced Hornet	Colonies usually become established in late Many and decline by September. Nests are usually found in shrubs, vines or trees and occasionally on power poles, houses and other man-made structures. The number of workers in an active colony at any one time can be as high as 600. Adults prefer live prey especially flies. This species is not a significant pest unless located in close proximity to sites of human activity.	April - September
Dolichovespula norvegicoides	N/A	Very little is known about this species of yellowjacket. The nests are aerial and very small.	Unknown
Vespula acadica	Forest Yellowjacket	Primarily a forest dwelling species whose nests may be aerial or in the ground. Colonies have been known to have as many as 400 workers at its peak. Adults are known to prey on caterpillars, flies and hemipterans. When disturbed adults are very aggressive.	Unknown
Vespula atropilosa	Prairie Yellowjacket	Typically found in prairie and open woodland areas as well as yards pastures and golf courses. Colonies are usually underground, frequently being found in rodent burrows. Nests have been found with as many as 500 active workers at its peak. Workers are predators on spiders, flies, caterpillars, hemipterans and some homopterans.	Four months spring to summer
Vespula austriaca	N/A	Rarely found. This species is an obligatory parasite of the Forest Yellowjacket (Vespula acadica) and does not have a worker caste like most other yellowjacket species. Forest Yellowjacket workers rear immature Vespula austriaca to produce new male and queen Vespula austriaca.	Unknown
Vespula consobrina	Black Jacket	Primarily a forest dwelling species whose nests are usually found in rodent burrows and sometimes above ground in logs, rock cavities and walls of man-made structures. Colonies are small with less than 150 workers at any given time. Adult prey are similar to the Prairie Yellowjacket (Vespula atropilosa) especially spiders. This species is strictly predatory in behavior.	Spring to early September
Vespula germanica	German Yellowjacket	A species of yellowjacket native to Europe which has been found in parts of California in the last few years. Nests can be found in the ground or in man-made structures. Colonies can be quite large with as many as 5,000 active workers at any one time. Adults utilize a wide range of arthropods, especially insects such as flies as hosts and are easily attracted to sweets. This species can be a pest to beekeepers and problematic in parks and marketplace areas. Adults can forage up to 1600 ft. from their nests.	March - November
Vespula pensylvanica	Western Yellowjacket	Nests are usually underground, commonly being found in rodent burrows. Colonies can be large with 5,000 workers at its peak. Adults have a wide range of prey including slugs, spiders, grasshoppers, flies, hemipterans and homopterans. This species is the most common pest yellowjacket in the Western United States. Population explosions of this yellowjacket can occur every few years, usually in conjunction with warm, dry springs.	April - October
Vespula sulphurea	California Yellowjacket	Little is known about this species of yellowjacket. Nests, when found, are usually underground. The maximum number of active workers found in any one nest was less than 1,100. This is not a common species and is not known to be a pest of picnic areas.	Spring to December
Vespula vulgaris	Common Yellowjacket	This is a common species in wooded areas. Most nests are subterranean, although logs, stumps and the like are also used as nesting sites. Adults usually prey on insects. Nests can be large containing as many as 5,000 workers.	May - October


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