Hot Topics

Could you be raising mosquitos in your backyard?

Are you finding dead birds? Here's what to do...

What is the district doing to fight West Nile Virus?

Request a Service Call...

View the current U.S. West Nile Virus human case counts as reported by the CDC...

See the California summaries of West Nile Virus Activity

Search for Material Safety Data Sheets

Wasps and Yellowjackets

It is the threat of a painful wasp sting that has most people concerned about the presence of wasps or a nearby nest. Only very rarely does a stinging incident occur. Most all of the time bees, wasps, yellowjackets and hornets are beneficial to humans or the eco system in some way. So even when a few wasps or bees are present it is best to leave them alone. However, there are times that control measures need to be taken.

To avoid the wasp's sting we should understand something about the life cycle and behavior of wasps. First, wasps can be broken into two groups.

Social Solitary
Yellowjackets Mud Dauber
Paper Wasps  

The solitary wasps rarely become a problem. Solitary means they do not colonize or form nests where many wasps live together. Although they may look threatening, most of them do not defend their nests and rarely sting people. Mud Daubers build a hard nest out of mud, usually on ceilings, walls or eaves of buildings. The nests are attended by a single female wasp. The mud dauber's favorite food is a spider meal. The Blue Mud Wasp is another solitary wasp less common but present in our area. This wasp seems incapable of building her own mud nest, but is able to repair and use abandoned nests. The Black Widow spider is at the top of her menu.

The social wasps can be fractured into 2 groups, the Yellowjackets / Hornets and Paper wasps. Most of these wasps feed on insect pests eliminating large numbers of them. Paper wasps feed abundantly on armyworms, corn earworms and other ag pests. Hornets will take house flies, blow flies and caterpillars. Other Yellowjacket species are exclusively scavengers. Unless they nest or are active near human activities, it's best to leave them alone. But unlike the solitary wasps, these wasps can become very defensive when their nests are disturbed. Loud noises such as a lawnmower, vibration from even footsteps or just coming too close to a nest can elicit a defensive response. Yellowjackets, hornets and paper wasps are attracted to some types of odors and sources of water. Swimming pools, ornamental ponds and other sources of standing water will be attractive to nest building workers. Foraging and scavenging workers may be attracted in differing degrees to clover, ripe or rotting fruit, pet food, garbage, soft drinks and a variety of cooked meats. Also perfumes, hair sprays, suntan lotion and other cosmetics may less frequently attract wasps, bees and yellowjackets.

Yellowjackets / Hornets

Yellowjackets and hornets are made up of several species of wasps in the genera Vespula and Dolichovespula. These different species build nests in vastly different places. Vespula pensylvanica is a ground nesting species, often called the meat bee. Vespula vulgaris commonly builds its nests in rotting tree stumps in higher elevations. Vulgaris germanica is found frequently in urban areas, sometimes nesting in houses. Dolichovespula maculata, the bald faced hornet, builds paper nests attaching them to eaves of buildings or limbs of a tree. Colonies of these species reach much higher numbers than the paper wasps. They can achieve populations between 1,500 and 15,000. Yellowjackets and hornets get involved in human activity as they are attracted to some of the same kind of foods humans are. Other meetings can occur when people inadvertently disturb a ground nest or nest in a wall or tree.

Paper Wasp

The paper wasp is made up of mostly the Polistes genus. They are easy to distinguish from other bees, hornets and yellowjackets as they are less aggressive and they build a hexagonal, open paper nest. Markings and colors vary but include yellows, browns and blacks. The nest is constructed in protected areas above the ground. Common areas their nests can be found include on walls or under eaves of homes and other buildings. Nest construction begins in the Spring and construction and maintenance continues as long as the colony continues to grow. Wasps gather fibers form old decaying wood or dead, dry plants, chew them up and mix the debris with water to make their grey paper nest. Populations in these nests rarely ever exceed 200.

Home | Sitemap | Contact Us