YELLOWJACKETS AND OTHER SOCIAL

Integrated Pest Management in and around the Home

Only a few of the very large number of a single queen who overwinters and species in California live a social becomes active when the weather life; these species are referred to as warms. She emerges in late winter/ social wasps. Some social wasps are early spring to feed and start a new predators for most or all of the year . From spring to midsummer and provide a great benefit by killing are in the growth phase, and the larvae large numbers of plant-feeding require large amounts of protein. and nuisance ; others are exclu- Workers forage mainly for protein at sively scavengers. Wasps become a this time (usually in the form of other problem only when they threaten to insects) and for some sugars. By late sting humans. One of the most trouble- summer, however, the colonies grow some of the social wasps is the yellow- more slowly or cease growth and re- jacket. Yellowjackets, especially quire large amounts of sugar to main- ground- and cavity-nesting ones such tain the queen and workers. So as the western yellowjacket (Fig. 1), foraging wasps are particularly inter- tend to defend their nests vigorously ested in sweet things at this time. when disturbed. Defensive behavior Figure 1. Western yellowjacket. increases as the season progresses and Normally, yellowjacket and paper colony populations become larger wasp colonies only live one season. In while food becomes scarcer. In fall, very mild winters or in coastal Califor- [=] maculata) on foraging yellowjackets are primarily nia south of San Francisco, however, the abdomen, and have a very short, scavengers and they start to show up some yellowjacket colonies survive for narrow waist (the area where the tho- at picnics, barbecues, around garbage several years and become quite large. rax attaches to the abdomen). cans, at dishes of dog or cat food placed outside, and where ripe or over- Yellowjackets Nests are commonly built in rodent ripe fruit are accessible. At certain The term yellowjacket refers to a num- burrows, but other protected cavities, times and places, the number of scav- ber of different species of wasps in the like voids in walls and ceilings of enger wasps can be quite large. genera Vespula and Dolichovespula houses, sometimes are selected as nest- (family ). Included in this ing sites. Colonies, which are begun IDENTIFICATION AND group of ground-nesting species are each spring by a single reproductive LIFE CYCLE the western yellowjacket, Vespula female, can reach populations of be- In western states there are two distinct pensylvanica, which is the most com- tween 1,500 and 15,000 individuals, types of social wasps: yellowjackets monly encountered species and is depending on the species. The wasps and paper wasps. Yellowjackets are by sometimes called the “meat ,” and build a nest of paper made from fibers far the most troublesome group. Paper seven other species of Vespula. Vespula scraped from wood mixed with saliva. wasps are much less defensive and vulgaris is common in rotted tree It is built as multiple tiers of vertical rarely sting humans. They tend to shy stumps at higher elevations and V. cells, similar to nests of paper wasps, away from human activity except germanica (the German yellowjacket) is but enclosed by a paper envelope when their nests are located near becoming more common in many ur- around the outside that usually con- doors, windows, or other high traffic ban areas of California, where it fre- tains a single entrance hole (Fig. 2). If areas. quently nests in houses. These wasps the rodent hole is not spacious tend to be medium sized and black enough, yellowjackets will increase the Nests of both yellowjacket and paper with jagged bands of bright yellow (or size by moistening the soil and dig- wasps typically are begun in spring by white in the case of the aerial-nesting ging. Similar behavior inside a house

PEST NOTES Publication 7450 University of California Agriculture and Natural Resources Revised August 2001 August 2001 Yellowjackets and Other Social Wasps

clothing. As with any stinging incident, it is best to leave the area of the nest site as quickly as possible if wasps start stinging.

Paper Wasps Paper wasps such as fuscatus aurifer, P. apachus, and P. dominulus are large (1 inch long), slender wasps with long legs and a distinct, slender waist (Fig. 3). Background colors vary, but most western species tend to be golden brown, or darker, with large patches of Figure 3. . yellow or red. Preferring to live in or near orchards or vineyards, they hang their paper nests in protected areas, such as under eaves, in attics, or under tree branches or vines. Each nest hangs like an open umbrella from a pedicel (stalk) and has open cells that can be seen from beneath the nest (Fig. 4). White, legless, grublike larvae some- times can be seen from below. Paper Figure 2. Yellowjacket nest in spring wasp nests rarely exceed the size of an (top), summer (center), and early fall outstretched hand and populations (bottom). vary between 15 to 200 individuals. Most species are relatively unaggres- sive, but they can be a problem when Figure 4. Paper wasp nest. sometimes leads to a wet patch that they nest over doorways or in other develops into a hole in a wall or areas of human activity, such as fruit ceiling. trees. wasps will crawl into soda cans and cause stings on the lips, or inside the Immature yellowjackets are white, Mud Daubers mouth or throat. grublike larvae that become white pu- Mud daubers are black and yellow, pae. The pupae develop adult coloring thread-waisted, solitary wasps that Responses to wasp stings vary from just before they emerge as adult wasps. build a hard mud nest, usually on ceil- only short-term, intense sensations to Immatures are not normally seen un- ings and walls, attended by a single substantial swelling and tenderness, less the nest is torn open or a sudden female wasp. They belong to the family some itching, or life-threatening aller- loss of adult caretakers leads to an Sphecidae and are not social wasps but gic responses. All these reactions are exodus of starving larvae. may be confused with them. They do discussed in detail in Pest Notes: Bee not defend their nests and rarely sting. and Wasp Stings (see “References”). Of Aerial-nesting yellowjackets, Dolicho- During winter, you can safely remove specific concern is a condition that vespula arenaria and D. maculata, build the nests without spraying. results from multiple-sting encounters, paper nests that are attached to the sometimes unfamiliar to attending eaves of a building or are hanging from INJURY OR DAMAGE health professionals, that is induced by the limb of a tree. The entrance is nor- Concern about yellowjackets is based the volume of foreign protein injected mally a hole at the bottom of the nest. on their persistent, pugnacious behav- and the tissue damage caused by de- These aerial nesters do not become ior around food sources and their ag- structive enzymes in wasp . Red scavengers at the end of the season, but gressive colony defense. Stinging blood cells and other tissues in the they are extremely defensive when behavior is usually encountered at body become damaged; tissue debris their nests are disturbed. Defending D. nesting sites, but scavenging and other breakdown products are arenaria sometimes bite and/or sting, yellowjackets sometimes will sting if carried to the kidneys, to be eliminated simultaneously. Wasp have no someone tries to swat them away from from the body. Too much debris and barbs and can be used repeatedly, es- a potential food source. When scaveng- waste products can cause blockages in pecially when the wasp gets inside ing at picnics or other outdoor meals, the kidneys, resulting in renal insuffi-

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ciency or renal failure. Patients in this it-yourself options include trapping frequently because yellowjackets are condition require medical intervention, wasps in a baited trap designed for not attracted to rotting meat. Also, even dialysis. that purpose, early-season removal of periodically check the trap to remove nests, or spraying the nest or nesting trapped yellowjackets and make sure MANAGEMENT site with an insecticide labeled for that workers are still attracted to the trap. Most social wasps provide an ex- use. tremely beneficial service by eliminat- Water Traps. Water traps are generally ing large numbers of other pest insects Trapping Wasps homemade and consist of a 5-gallon through predation and should be pro- Trapping wasps is an ongoing effort bucket, string, and protein bait (turkey tected and encouraged to nest in areas that needs to be initiated in spring and ham, fish, or liver works well; do not of little human or activity. Al- continued into summer and fall, espe- use cat food because it may repel the though many prey on social cially when the yellowjacket popula- yellowjackets after a few days). The wasps (including birds, reptiles, am- tion was large the previous year. In bucket is filled with soapy water and phibians, , bears, raccoons, spi- spring there is a 30- to 45-day period the protein bait is suspended 1 to 2 ders, preying mantids, and bald-faced when new queens first emerge before inches above the water. (The use of a ), none provides satisfactory they build nests. Trapping queens dur- wide mesh screen over the bucket will biological control in home situations. ing this period has the potential to help prevent other animals from reach- provide an overall reduction in the ing and consuming the bait.) After the The best way to prevent unpleasant yellowjacket population for the season, yellowjacket removes the protein, it encounters with social wasps is to and a study is currently underway to flies down and becomes trapped in the avoid them. If you know where they test this theory in some California Mos- water and drowns. Like the lure trap, are, try not to go near their nesting quito and Vector Control districts (see these traps also work best as queen places. Wasps can become very defen- “Online References”). The more traps traps in late winter to early spring. In sive when their nest is disturbed. Be on put out in spring on an area-wide basis summer and fall they may assist in the lookout for nests when outdoors. to trap queens, the greater the likeli- reducing localized foraging workers Wasps that are flying directly in and hood of reducing nests later in the but usually not to acceptable levels. out of a single location are probably summer. Usually one trap per acre is Place them away from patio or picnic flying to and from their nest. adequate in spring for depletion trap- areas so wasps aren’t attracted to your ping of queens; in fall, more traps may food as well. Scavenging wasps will not usually be necessary to trap scavenging wasps, become a problem if there is no food depending on the size of the popula- Discouraging or around to attract them. When nuisance tion. There are two types of wasp Eliminating Nests wasps are present in the outdoor envi- traps: lure and water traps. Early in the season, knocking down ronment, keep foods (including pet newly started paper wasp nests will food) and drinks covered or inside the Lure Traps. Lure traps are available for simply cause the founding female to go house and keep garbage in tightly purchase at many retail stores that sell elsewhere to start again or to join a sealed garbage cans. Once food is dis- pest control supplies and are easiest to neighboring nest as a worker. As there covered by wasps, they will continue use. They work best as queen traps in is little activity around wasp nests to hunt around that location long after late winter and spring. In summer and when they are first starting, they are the source has been removed. fall they may assist in reducing local- very hard to find. Wasps are more ized foraging workers, but they do not likely to be noticed later after nests and If wasp nests must be eliminated, it is eliminate large populations. Lure traps populations grow. Nest removal for easiest and safest to call for profes- contain a chemical that attracts yellow- controlling subterranean or cavity- sional help. In some areas of California, jackets into the traps, but common dwelling yellowjackets is not practical personnel from a local Mosquito and lures such as heptyl butyrate are not because the nests are underground or Vector Control District may be avail- equally attractive to all species. Pro- otherwise inaccessible. able to remove nests. To determine if teins such as lunchmeat can be added this service is available in your area, as an attractant and are believed to Nest Sprays call the California Mosquito and Vector improve catches. Aerosol formulations of insecticides on Control Association at (916) 440-0826. the market labeled for use on wasp and During spring, baited lure traps should nests can be effective against If a rapid solution to a severe yellow- have the chemical bait changed every 6 both yellowjackets and paper wasps, jacket problem is essential, seek the to 8 weeks. In summer, change the bait but they must be used with extreme assistance of a professional pest control every 2 to 4 weeks; change bait more caution. Wasps will attack applicators operator who can use microencapsu- frequently when temperatures are when sensing a poison applied to their lated baits to control these pests. Do- high. Meats must be replaced more nests, and even the freeze-type prod-

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ucts are not guaranteed to stop all intoxicated, agitated wasps are likely Ebeling, W. 1975. Urban Entomology. wasps that come flying out. It is pru- to be encountered at some distance Oakland: Univ. Calif. Agric. Nat. Sci. dent to wear protective clothing that from the nest entrance, even on the day covers the whole body, including following an insecticidal treatment. Mussen, E. Feb 1998. Pest Notes: Bee and gloves and a veil over the face. In addi- Hiring a pest control professional will Wasp Stings. Oakland: Univ. Calif. tion, you need to wear protective reduce risks to you and your family; in Agric. Nat. Res. Publ. 7449. Also avail- eyewear and other clothing to protect some areas of California, this service able online at www.ipm.ucdavis.edu/ yourself from pesticide hazards. Wasps may be available through your local PMG/selectnewpest.home.html are most likely to be in the nest at Mosquito and Vector Control District. night. But even after dark and using Online References formulations that shoot an insecticide REFERENCES California Mosquito and Vector Control stream up to 20 feet, stinging incidents Akre, R. D., A. Green, J. F. MacDonald, Web site (www.sac-yolomvcd.com) for are likely. Underground nests can be P. J. Landolt, and H. G. Davis. 1981. information on yellowjacket control quite a distance from the visible en- The Yellowjackets of America North of trance and the spray may not get back Mexico. USDA Agric. Handbook No. far enough to hit the wasps. Partially 552. 102 pp.

For more information contact the University of California Cooperative Extension or agri- cultural commissioner’s office in your coun- ty. See your phone book for addresses and phone numbers.

AUTHOR: E. Mussen EDITOR: B. Ohlendorf TECHNICAL EDITOR: M. L. Flint DESIGN AND PRODUCTION: M. Brush ILLUSTRATIONS: Fig. 1: Courtesy of U.S. Public Health Service; Fig. 2: A. L. Antonel- li. Modified after Washington State Universi- ty Bulletin EB 0643, Yellowjackets and Paper Wasps. Figs. 3 and 4: D. Kidd.

Produced by IPM Education and Publica- tions, UC Statewide IPM Project, University of California, Davis, CA 95616-8620 WARNING ON THE USE OF CHEMICALS This Pest Note is available on the World Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed, Wide Web (http://www.ipm.ucdavis.edu) away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens containing fruits or vegetables ready to be picked. Do not place containers containing pesticide in the trash nor pour pesticides down sink or toilet. Either use the pesticide according to the label or take unwanted pesticides to a Household Hazardous Waste Collection site. Contact your county agricultural commissioner for additional information on safe container disposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose of This publication has been anonymously peer empty containers by following label directions. Never reuse or burn the containers or dispose of them in such reviewed for technical accuracy by University of a manner that they may contaminate water supplies or natural waterways. California scientists and other qualified profes- sionals. This review process was managed by the ANR Associate Editor for Pest Management. The University of California prohibits discrimination against or harassment of any person employed by or To simplify information, trade names of products seeking employment with the University on the basis of race, color, national origin, religion, sex, physical have been used. No endorsement of named products or mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status, is intended, nor is criticism implied of similar products age, sexual orientation, citizenship, or status as a covered veteran (special disabled veteran, Vietnam-era that are not mentioned. veteran, or any other veteran who served on active duty during a war or in a campaign or expedition for which This material is partially based upon work a campaign badge has been authorized). University policy is intended to be consistent with the provisions supported by the Extension Service, U.S. Department of applicable State and Federal laws. Inquiries regarding the University’s nondiscrimination policies may be of Agriculture, under special project Section 3(d), directed to the Affirmative Action/Staff Personnel Services Director, University of California, Agriculture and Integrated Pest Management. Natural Resources, 300 Lakeside Dr., Oakland, CA 94612-3350; (510) 987-0096.

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