Yellow Jackets

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Only a few of the very large number ofwasp species in California live a sociallife. These species are referred to as socialwasps. Some social wasps are predators formost or all of the year and provide a greatbenet by kill ing large numbers of plant-feeding insects and nuisance ies; othersare exclusively scavengers. Wasps becomea problem only when they threaten to stinghumans. In California, yellowjackets arethe primary pests among the social wasps.

IDENTIFICATION ANDLIFE CYCLE

In Western states there are two distinct

types of social waspsyellowjackets andpaper wasps. Yellowjackets are by farthe most troublesome group, especiallyground- and cavity-nesting ones such as thewestern yellowjacket (Figure 1), which tendto defend their nests vigorously when dis-turbed. Defensive behavior increases as theseason progresses and colony populations

become larger while food becomes scarcer.In fall, foraging yellowjackets are primar-ily scavengers, and they start to show up atpicnics and barbecues, around garbage cans,at dishes of dog or cat food placed outside,and where ripe or overripe fruit are accessi-

ble. At certain times and places, the numberof scavenger wasps can be quite large.

Paper wasps are much less defensive andrarely sting humans. They tend to shyaway from human activity except whentheir nests are located near doors, win-dows, or other high-trafc areas.

Typically, previously mated, overwinteringyellowjacket and paper wasp queens begintheir nests in spring when the weatherbecomes warm. The queen emerges in latewinter to early spring to feed and starta new nest. From spring to midsummer,nests are in the growth phase, and larvaerequire large amounts of protein. Workersforage mainly for protein at this timeusually other insectsand for some sug-

ars. By late summer, however, the coloniesgrow more slowly or cease growth andrequire large amounts of sugar to maintainthe queen and workers; foraging wasps

are particularly interested in sweet thingsat this time. Normally, yellowjacket andpaper wasp colonies live only one season.In very mild winters or in coastal Califor-nia south of San Francisco, however, someyellowjacket colonies survive for severalyears and become quite large.

Yellowjackets

The term yellowjacket refers to a numberof different species of wasps in the generaVespula and Dolichovespula (family Vespidae).Included in this group of ground-nestingspecies are the western yellowjacket, V. pen-

sylvanica, which is the most commonly en-countered species and issometimes calledthe meat bee, and seven other species ofVespula. V. vulgaris is common in rotted treestumps at higher elevations, and V. german-ica, the German yellowjacket, is becomingmore common in many urban areas of Cali-fornia, where it frequently nests in houses.

These wasps tend to be medium sizedand black with jagged bands of brightyellowor white in the case of the aerial-nesting D. (formerly known as V.) macu-lataon the abdomen and have a veryshort, narrow waist, the area where thethorax attaches to the abdomen.

Yellowjackets commonly build nests inrodent burrows (Figure 2), but they some-

Integrated Pest Management for Home Gardeners and Landscape Professionals

Yellowjacketsand othersocial wasps

Statewide Integrated Pest Management Program March 2012

PEST NOTES Publication 7450

Figure 1. Western yellowjacket.

Figure 2. Yellowjacket nest inan underground rodent burrowin spring (top), summer (center),

and early fall (bottom). The nestbecomes larger during the summeras yellowjackets add new comblayers, each containing developinglarvae. The colony declines in latefall when workers die off.


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March 2012 Yellowjackets and Other Social Wasps

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times select other protected cavities, suchas voids in walls and ceilings of houses,as nesting sites. Colonies, which are be-gun each spring by a single reproductivefemale, can reach populations of between1,500 and 15,000 individuals, dependingon the species.

The wasps build a nest of paper madefrom bers scraped from wood mixedwith saliva. It is built as multiple tiersof vertical cells, similar to nests ofpaper wasps, but enclosed by a paperenvelope around the outside that usu-ally contains a single entrance hole. Ifthe rodent hole isnt spacious enough,yellowjackets will increase the size bymoistening the soil and digging. Simi-lar behavior inside a house sometimesleads to a wet patch that develops intoa hole in a wall or ceiling.

Immature yellowjackets are whitegrublike larvae that become white pu-pae. The pupae develop adult coloringjust before they emerge as adult wasps.Immatures normally arent seen unlessthe nest is torn open or a sudden loss ofadult caretakers leads to an exodus ofstarving larvae.

Aerial-nesting yellowjackets, D. arenariaand D. maculata, build paper nests that

they attach to the eaves of a building orthat hang from the limb of a tree. Theentrance normally is a hole at the bottomof the nest. These aerial nesters dont be-come scavengers at the end of the season,

but they are extremely defensive whentheir nests are disturbed. Defending D.arenaria sometimes bite and sting simul-taneously. Wasp stingers have no barbsand can be used repeatedly, especiallywhen the wasp gets inside clothing. Aswith any stinging incident, it is best toleave the area of the nest site as quicklyas possible if wasps start stinging.

Paper Wasps

Paper wasps such as Polistes fuscatusaurifer, P. apachus, and P. dominulusare 1-inch-long slender wasps withlong legs and a distinct slender waist(Figure 3). Background colors vary, butmost Western species tend to be golden

brown or darker with large patches ofyellow or red.

Preferring to live in or near orchardsor vineyards, they hang their papernests in protected areas, such as undereaves, in attics, or under tree branchesor vines. Each nest hangs like an openumbrella from a pedicel (stalk) andhas open cells that can be seen from

beneath the nest (Figure 4). Some-times white, legless, grublike larvaecan be seen from below. Paper waspnests rarely exceed the size of an out-stretched hand, and populations vary

between 15 to 200 individuals. Mostspecies are relatively unaggressive, butthey can be a problem when they nestover doorways or in other areas of hu-man activity such as fruit trees.

Mud Daubers

Mud daubers (Figure 5) are black andyellow thread-waisted solitary waspsthat build a hard mud nest, usually onceilings and walls, attended by a singlefemale wasp. They belong to the familySphecidae and arent social wasps butmight be confused with them. Theydont defend their nests and rarelysting. During winter, you can safelyremove the nests without spraying.

INJURY AND DAMAGE

Concern about yellowjackets is based

on their persistent, pugnacious be-havior around food sources and theiraggressive defense of their colony.Usually stinging behavior is encoun-tered at nesting sites, but sometimesscavenging yellowjackets will sting ifsomeone tries to swat them away froma potential food source. When scaveng-ing at picnics or other outdoor meals,wasps will crawl into soda cans andcan sting your lips or the inside of yourmouth or throat.

Reactions to wasp stings vary from

only short-term, intense sensations tosubstantial swelling and tenderness,some itching, or life-threatening al-lergic responses. These reactions arediscussed in detail in Pest Notes:Beeand Wasp Stings. (See References.) Ofspecic concern is a condition thatresults from multiple-sting encounters,sometimes unfamiliar to attendinghealth professionals, that is induced

by the volume of foreign protein in-jected and the tissue damage caused bydestructive enzymes in wasp venom.Red blood cells and other tissues in thebody become damaged, and tissue de-bris and other breakdown products arecarried to the kidneys, to be eliminatedfrom the body. Too much debris andwaste products can cause blockages inthe kidneys, resulting in renal insuf-ciency or renal failure. Patients in thiscondition require medical intervention,which can include dialysis.

MANAGEMENT

Most social wasps provide an extremelybenecial service by eliminating largenumbers of other pest insects throughpredation and should be protected andencouraged to nest in areas of little hu-man or animal activity. Although manyanimals prey on social waspsinclud-ing birds, reptiles, amphibians, skunks,

Figure 3. Paper wasp.

Figure 4. Paper wasp nest.

Figure 5. Mud dauber.


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bears, raccoons, spiders, praying man-tids, and bald-faced hornetsnoneprovides satisfactory biological controlin home situations.

The best way to prevent unpleasant

encounters with social wasps is toavoid them. If you know where theyare, try not to go near their nestingplaces. Wasps can become very defen-sive when their nest is disturbed. Beon the lookout for nests when outdoors.Wasps that are ying directly in andout of a single location are probably y-ing to and from their nest.

Usually, scavenging wasps wont be-come a problem if there is no foodaround to attract them. When nuisancewasps are present outdoors, keep foodsincluding pet food and drinks coveredor inside the house, and keep garbagein tightly sealed garbage cans. Oncewasps discover food, they will continueto hunt around that location long afterthe source has been removed.

If wasp nests must be eliminated, itis easiest and safest to call for profes-sional help. In some areas of California,personnel from a local mosquito andvector control district may be availableto remove nests. To determine if this

service is available in your area, callthe Mosquito & Vector Control Associ-ation of California at (916) 440-0826. If arapid solution to a severe yellowjacketproblem is essential, seek the assistanceof a professional pest control operatoror consider installing bait stations.

Trapping Wasps

Trapping is one method that can beemployed to try to reduce yellowjacketproblems. Trapping isnt suggested forother social wasp species.

Lure traps. The easiest to use are luretraps (Figure 6), which are availablefor purchase at many retail stores thatsell pest control supplies. Lure trapscan help reduce the number of local-ized foraging workers, but they donteliminate large populations. Lure trapscontain a chemical that attracts yellow-jackets into the traps, but the commonlure in traps, heptyl butyrate, attracts

primarily the western yellowjacketand not other species. Meat such aschicken can be added as an attractantand is believed to improve catches ofthe German yellowjacket and V. vul-

garis. Replace meat frequently, because

yellowjackets arent attracted to rottingmeat. Also, periodically check the trapto remove trapped yellowjackets andmake sure workers are still attractedto the trap. Lures need to be replacedperiodically; follow trap directionsregarding replacement.

To reduce the number of yellowjacketsforaging in specic areas such as pa-tios, picnic tables, concession stands,and Dumpsters, place lure traps withhepytl butyrate around the periphery.

In large areas such as parks, place trapsabout 200 feet from the area to be pro-tected and about every 150 feet alongthe circumference. In backyards, placethem along the edge of the propertyline as far away from the patio or otherprotected area as possible. To interceptforaging yellowjackets, it is importantto place the traps between the area to

be protected and the native landscapesserving as nesting sites. Typically yel-

lowjackets will forage about1/4 mile.See Figure 7 for a suggested placement

for traps.

Water traps. Water traps generally arehomemade and consist of a 5-gallon

bucket, string, and protein bait such asturkey, ham, sh, or liver. Fill the bucketwith soapy water, and suspend the pro-

Figure 6. Yellowjacket lure trap.

Figure 7. Placement of lure traps (represented by stars) to protect a picnic area in apark. Place the traps about 200 feet from the protected area and about 150 feet apart.In a backyard situation, place the traps around the per iphery of the property as faraway from the patio or other protected area as possible.

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Picnic area

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tein bait 1 to 2 inches above the water. Awide mesh screen over the bucket willhelp prevent other animals from reachingand consuming the bait. After the yellow-jacket removes the protein, the yellow-jacket ies down and becomes trapped inthe water and drowns. Like the lure trap,these traps also work best as queen trapsin late winter to early spring. In summerand fall they might assist in reducinglocalized foraging workers but usuallynot to acceptable levels. Place water trapsaway from patio or picnic areas, so waspsarent attracted to your food as well.

Bait Stations

In the past, poison bait products wereavailable to reduce yellowjacket popula-tions later in the season when their prey

is no longer available and some speciesturn to scavenging. However, reliableproducts were taken off the market in theearly 2000s. Esfenvalerate products thatrecently became available havent beenshown to be effective in research trials.

Discouraging orEliminating Nests

Early in the season, simply knockingdown newly started paper wasp nestswill cause the founding female to goelsewhere to start again or to join aneighboring nest as a worker. As thereis little activity around newly startedwasp nests, they are very difcult tond. Wasps are more likely to be no-ticed after nests and populations grow.Nest removal for controlling subterra-nean or cavity-dwelling yellowjacketsisnt practical, because the nests areunderground or otherwise inaccessible.

Nest Sprays

Aerosol formulations of insecticides la-beled for use on wasp a nd hornet nestscan be effective against yellowjackets

and paper wasps, but the products mustbe used w ith extreme caution. Waspswill attack if they sense a poison be-ing applied to their nests, and even thefreeze-type products arent guaranteedto stop all wasps that come ying out. Itis prudent to wear protective clothingthat covers the entire body, includinga veil over your face and gloves. Inaddition, you need to wear protective

eyewear and other clothing to protectyourself from pesticide hazards.

Wasps are most likely to be in the nestat night, but even after dark and usingformulations that shoot an insecticidestream up to 20 feet, stinging inci-dents are likely. Underground nestscan be quite a distance from the vis-ible entrance, and the spray might notget back far enough to hit the wasps.Partially intoxicated, agitated waspsare likely to be encountered at somedistance from the nest entrance, eventhe day after an insecticidal treatment.Hiring a pest control professional willreduce risks to you and your family; insome areas of California, this servicemight be available through your local

mosquito and vector control district.

REFERENCES

Akre, R. D., A. Green, J. F. MacDonald,

P. J. Landolt, and H. G. Davis. 1981.

The Yellowjackets of America North of

Mexico. USDA Agric. Handbook No.

552.

Ebeling, W. 1975. Urban Entomology.Oakland: Univ. Calif. Agric. Nat. Res.

Mussen, E. C. Sept. 2011. Pest Notes: Beeand Wasp Stings. Oakland: Univ. Calif.Agric. Nat. Res. Publ. 7449. Also avail-able online, www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7449.html.

SUGGESTED READING

Sacramento-Yolo Mosquito & Vector

Control District, www.ghtthebite.net.v

AUTHORS:E. C. Mussen, Entomology, UCDavis; and M. K. Rust, Entomology, UC Davis.

TECHNICAL EDITOR: M. L. Flint

EDITOR: M. L. Fayard

ILLUSTRATIONS:Figs. 1, 3, and 56,

J. K. Clark; Fig. 2, A. L. Antonelli from

Yellowjackets and Paper Wasps. Pullman:

Wash. State Univ. Bul. EB 0643; Fig. 4, L. L.

Strand; and Fig. 7, M. K. Rust.

This and other Pest Notes are available at

www.ipm.ucdavis.edu.

For more information, contact the University of

California Cooperative Extension ofce in your

county. See your telephone directory for addresses

and phone numbers, or visit http://ucanr.org/ce.cfm.

WARNING ON THE USE OF CHEMICALSPesticides 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,away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock.

Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans.Conne chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardenscontaining fruits or vegetables ready to be picked.

Do not place containers containing pesticide in the t rash or pour pesticides down the sink or toilet. Either usethe pesticide according to the label, or take unwanted pesticides to a Household Hazardous Waste Collectionsite. Contact your county agricultural commissioner for additional information on safe container disposal andfor the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containersby following label directions. Never reuse or burn the containers or dispose of them in such a manner thatthey may contaminate water supplies or natural waterways.

ANR NONDISCRIMINATION AND AFFIRMATIVE ACTION POLICY STATEMENTThe University of California prohibits discrimination or harassment of any person in any of its programs

or activities. The complete nondiscrimination policy statement can be found at http://ucanr.org/sites/anrstaff/les/107734.doc. Inquiries regarding the universitys equal employment opportunity policies may be directedto Linda Marie Manton, Afrmative Action Contact, University of California, Davis, Agriculture and NaturalResources, One Shields Avenue, Davis, CA 95616, (530) 752-0495.

Produced by UC Statewide

Integrated Pest Management ProgramUniversity of California, Davis, CA 95616

University of California scientists and otherqualied professionals have anonymously peerreviewed this publication for technical accuracy. TheANR Associate Editor for Urban Pest Managementmanaged this review process.

To simplify information, trade names of productshave been used. No endorsement of named productsis intended, nor is criticism implied of similar productsthat are not mentioned.

This material is partially based upon worksupported by the Extension Service, U.S. Departmentof Agriculture, under special project Section 3(d),Integrated Pest Management.

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Yellow Jackets