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.
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.
Adult Activity Period: April – October