Paper Wasps, Yellowjackets

and Solita ry Wasps

7-03

Glen C. Moore and Mike E. Merchant*

Several kinds of stinging wasps can pose seri-ous health and safety threats to humans.Most problems occur when people are stung

after getting too close to wasp nests constructednear homes, buildings and recreational areas. Insuch situations, it may be necessary to controlthe wasps, even though most wasps are benefi-cial pollinators and predators of other insects.

Although thousands of North American waspspecies can “sting,” few are potentially dangerous tohumans. Of the fewer than 40 species of stinging(vespid) wasps that occur in the United States, only ahandful are important stinging pests in Texas. Thispublication reviews the most important and commonspecies likely to be found around the home.

Kinds of WaspsAll wasps, bees and ants belong to the scientific

order called Hymenoptera. The Hymenoptera com-prise some of the most interesting and importantinsects, including many species that are beneficialpredators and parasites of pest insects, and many use-ful pollinator species. Besides ants and bees, the mostimportant stinging Hymenoptera belong to the waspfamily Vespidae.

Most vespid wasps are social insects, living in neststhat they build and defend cooperatively. The stingerof social wasps is primarily a defensive tool, designedto protect both nest and colony. However, whendefending a colony, multiple wasp stings can occurquickly, with each wasp stinging one or more times.Vespid wasp nests are constructed of a paper-like

material and may be found eitherabove or below ground.

Another important group of waspswith stingers are the solitary wasps.The stinger of solitary wasps is usedprimarily for subduing prey. Althoughsolitary wasps may be common andare often thought dangerous by peo-ple who fear wasps, solitary waspsrarely sting humans. Most are entire-ly beneficial, feeding on spiders,crickets, cicadas and caterpillars.Knowing how to distinguish betweensolitary and social wasps can be use-ful in determining whether control isjustified.

Wasp StingsWasps sting their victims and

inject venom from the rear of theabdomen (tail). The stinger in all

*Extension Agent, IPM and Associate Professor and Extension Entomologist; Texas Cooperative Extension

Paper Wasp (Polistes exclamans )neevlIcM dnalraG – otohP(.tsen no )

E-239

wasps and bees is a modified egg-laying organ(ovipositor); hence only females can sting.

Venom from ant, bee and wasp stings is responsi-ble for 40 to 100 deaths per year in the United States.Social wasp and bee venom contains more than 30compounds, including biogenic amines, protein toxinsand various enzymes. Most deaths from insect stingsare the result of allergic reactions to venom proteinsand enzymes.

Wasp stings typically result in intense pain, withswelling and redness at the site of the sting. Stingsaround the head, eyes and neck are especially serious.While pain is usually localized at the site of the sting,large local and systemic (allergic) reactions are alsopossible. Large local reactions occur when swellingand pain extends beyond two inches from the site ofthe sting. Swelling may involve an entire extremity,such as a hand, arm or leg. Large local reactions areusually not life-threatening, but may last for two toseven days. About 5 percent of people who experi-ence a large local reaction will suffer an anaphylactic(serious systemic hypersensitivity) reaction if they arestung subsequently.

Systemic allergic reactions occur when symptomsare produced in body sites other than at the site ofthe sting. These reactions — anaphylaxis or anaphy-lactic reactions — range from a widespread rash,swelling and itching to difficulty breathing. In severereactions, victims may develop a rapid pulse and lowblood pressure, shock or respiratory distress and evendeath. Respiratory conditions account for more thanhalf of all deaths due to Hymenoptera stings.

Anaphylaxis typically occurs within 20 to 30 min-utes of a sting, although shock and death can occur asquickly as 10 to 15 minutes. It is critical to get some-one experiencing a systemic reaction to emergencycare immediately. If you know that you are allergic tobee or wasp venom, consult your physician to seewhether you should carry an epinephrine emergencykit or self-administer an antihistamine for life-savingpurposes.

When Do Wasps Sting?Vespid wasps are most likely to sting when their

nest is disturbed. All social wasps will vigorouslydefend their nests when disturbed. These waspsrarely sting away from the nest, unless trapped orpressed against the skin.

Wasps and bees are instinctively attracted to theupper bodies of animals, so in the event of an attackit is best to cover your head and run away quickly.The best defense is to run to a building, car or otherprotected place. Victims who stand in place andattempt to swat their attackers will continue toreceive stings as the wasps summon reinforcementsvia chemical communication. Unlike honey bees,

wasps do not leave a stinger in the skin and may stingrepeatedly.

Solitary wasps, on the other hand, rarely stingunless mishandled or trapped against the skin. Thevenom of solitary wasps is different from that ofsocial wasps and seldom causes more than momen-tary pain. Because solitary wasps do not build a com-munity nest, they do not attempt to defend their nest.

Social WaspsPaper Wasps

Paper wasps are one of the most common vespidwasps seen around homes and buildings. They are 3/4to 1 inch long and generally reddish-orange to darkbrown. They often have yellow body markings. Paperwasps have three castes — infertile female workers,which make up most of the wasps on nests during thesummer; males; and queens. Males and new queensare produced primarily in late summer and fall.Unlike yellowjackets and hornets, the paper waspqueen is not much larger than the worker wasps.Paper wasps build their nests from chewed woodfibers. The comb, which hangs from a single filament,is usually oriented downward and consists of a singletier of hexagonal-shaped cells. Nests are most fre-quently seen under the eaves of houses but may alsobe found in attics, garages, storage sheds, barns, onshrubbery, trees and a variety of protected sites. Thetypical mature paper wasp nest contains 20 to 30adults and rarely more than 200 cells.

Life cycle. Colonies are founded in the spring byqueens that spend the winter in sheltered hidingplaces. Although early season queens may cooperatein founding a nest, by midsummer there is usuallyonly one active egg-laying queen per nest. New nestsare constructed every year, often in the same generallocation where nests were built the previous season.

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Paper wasp (Polistes carolina) foundresses. When a wasp colony has morethan one foundress the size of the nest increases rapidly. However, only onefoundress becomes the queen. (Photo – Garland McIlveen)

Queen paper wasps lay a single egg per nest cell.The newly hatched paper wasp larva is white and leg-less. As it grows in size, it fills the nest cell. Thequeen, and later the workers, bring food to the larva.Eventually, the larva matures, the cell is closed andpupation occurs. After pupation, the adult waspemerges by chewing through the paper cell cover.

During late summer and fall, males and queenpaper wasps are produced. Males and females mate inthe fall. The males then die, and fertilized queensenter sheltered locations for hibernation.

Overwintering paper wasp queens may join togeth-er, sometimes in large groups. They seem to preferhigh structures, such as the peaked attics of houses,chimneys and tall buildings. During the winter, theyfrequently enter homes and offices, especially duringwarmer periods. Overwintering paper wasps are notaggressive and may be captured and released out-doors or killed with a fly swatter.

Control. Aerial nests of paper wasps can easily beeliminated using rapid knock-down insecticides oraerosol products specifically designed for this pur-pose. Wasp sprays frequently contain the insecticidespyrethrins, resmethrin, tetramethrin, bifenthrin,cyfluthrin, lambda-cyhalothrin or permethrin.Products containing carbaryl, acephate and dichlorvosare also available for treating wasp colonies. Someaerosol containers will propel the insecticide 10 to 40feet or more.

For best results, treat in the late evening whenmost wasps have returned to the nest. When spray-ing, stand well away from the colony and soak thenest thoroughly. Do not remove the nest until all thewasps are dead, which may require up to 2 days.Then the nest should be removed and discarded.

YellowjacketsYellowjackets are easily recognized but are often

confused with paper wasps. Baldfaced hornets arealso a type of yellowjacket wasp, but because of somebehavioral differences, they will be discussed sepa-rately.

Worker yellowjackets construct their nests of apaper-like material consisting of wood fiber. Unlikepaper wasp nests, they are completely enclosed in anenvelope except for the entrance hole. In Texas, south-ern yellowjacket nest size may varyfrom a few inches to 6 feet or larger,and nests may contain up to 45 levelsof combs and 20,000 adult workers.Yellowjackets are primarily groundnesters, but they also construct aerialnests. Subterranean nests may befound in gardens, flower beds, pas-tures, roadside embankments and else-where. Aerial nests are typically con-structed in trees, under eaves, in wall

voids of buildings, in open garages and storage sheds,on porches, in abandoned furniture and in otherplaces that provide protection and are close to foodand water. Because of their scavenging behavior, yel-lowjackets are a menace around parks, camps andsuburban sites where people leave open food and dis-card garbage.

Yellowjacket workers forage to feed their larvaeinsects and spiders. They also gather nectar, honey-dew and other carbohydrates, but they do not storehoney as do bees.

Colony founding. Yellowjacket queens overwinterunder loose bark, in cracks and crevices and occasion-ally in attics or similar sheltered locations. Theyemerge during the early spring and build small papernests in which they lay eggs. When the eggs hatch,the queens feed the young larvae for about 18 to 20days. After the first brood of workers emerge, the nestmay rapidly expand up to a foot long or larger withina few days or weeks. Maximum colony size isattained by August or September. This is followed bythe emergence of males and next year’s queens inOctober and November. After mating, the males dieand inseminated queens usually seek sheltered placesto overwinter, abandoning the nest. Abandoned nestsrapidly decompose and are not reused the next year.Occasionally, in sheltered sites or during mild win-ters, the nest may not be abandoned. In such cases,so-called perennial colonies may be maintained byboth queen(s) and workers into the following year.Perennial colonies are generally larger than annualcolonies.

Control. If not too close to areas of human activity,yellowjacket nests should be left alone and the areamarked with a warning sign. In late fall or early win-ter, after the firsthard frost, mostyellowjacket nestsdie; abandonednests can beplugged up (withor without treat-ment) to preventfurther infesta-tions next year.

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Yellowjacket nest and yellowjacket work-ers (Vespuls squamosa) at entrancehole. (Photo – Garland McIlveen)

Wasp control is dangerous and should not beundertaken by anyone with a heart condition orknown allergies to bee or wasp venom. If you haveany doubt about your ability to safely control a waspnest, call a professional.

Underground yellowjacket wasp nests are besttreated with an insecticide dust. Dusts have theadvantage that they can be tracked deep into the nestby wasps as they enter and exit. Crank or power-typedusters can be used to blow dust into a wasp nestentrance. A hose or plastic tube can be used to extendthe reach of the duster into otherwise inaccessiblenest entrances. Effective dusts include those contain-ing carbaryl, esfenvalerate and permethrin. Be surethe products have a label that allows their use oninsect nests in the soil. Use of acephate dusts underor around homes should be avoided because of thepotential for indoor odor problems.

Aerosol sprays can also be used but may have alower success rate unless sufficient aerosol can beinjected directly into the nest entrance. Liquid insecti-cides applied as a spray are generally less effective onsubterranean nests, as they often soak into soil andmay not reach the nest in a sufficient quantity toeliminate a colony.

Garbage cans can be attractive to foraging yellow-jacket wasps at certain times of year. At such times, itis especially important to ensure that all garbagereceptacles are closed tightly when not in use andemptied daily. Yellowjacket wasp traps are commer-cially available and may help to reduce foraging num-bers somewhat when properly maintained. However,these devices do not effectively control wasp colonies.

Horn etsThe term hornet is often used in a general sense to

describe many kinds of wasps and yellowjackets.Actually, the baldfaced hornet, Dolichovespula macu-lata, is the only “hornet” reported in Texas. Hornetsconstruct a round or pear-shaped papernest, up to 3 feet long. The grayish tobrown nest has two to four horizontallyarranged combs inside and an entrancehole near the bottom.

Hornet nests almost always are above ground,often high in trees. Occasionally, they may beattached to the eaves of buildings. A mature colonymay contain 200 to 400 adults.

While the stings of hornets can be intenselypainful, hornets are less likely to attack than paperwasps or yellowjacket wasps. Hornets typically nesthigh in trees or in other remote locations, where theypose no threat to humans and should be left undis-turbed. When control is needed, apply a liquid insec-ticide from a safe distance of at least 10 to 15 feet.Control products that include a refrigerant agent areoften used to quickly immobilize stinging insects.Most residual insecticides such as permethrin,cyfluthrin, bifenthrin, esfenvalerate, tetramethrin,acephate and carbaryl will control hornet nests.Pressurized aerosols designed for wasp control, pinstream sprays from a good garden sprayer or spraystreams from a hose-end sprayer should be directedtoward the nest entrance and the nest thoroughlysoaked with spray.

Insecticide products containing synergizedpyrethrins and a rapidly volatilizing organic solvent,such as Wasp Freeze, can be extremely useful. Treat-ment should be directed into the opening of the nest.Hornet nests high in trees or in other remote loca-tions where they pose no threat to humans should beleft unharmed. When attempting to control baldfacedhornets, always wear protective clothing, such as abee suit, or hire a professional pest control operator.

Solita ry WaspsCicada Killers

This large insect is 11/2 inches long, rusty red onthe head, thorax and wings and striped with blackand yellow on the abdomen. These wasps may beconsidered a nuisance in landscapes during times ofthe year when cicadas are present in shade trees.Cicada killer wasps appear formidable because of

their size and behavior. Male cicadakillers cannot sting but will buzz verynear humans. Females will not stingunless handled but sometimes painfullysting people who are working on lawnsor step on their nests barefooted. Femalecicada killers dig galleries in lawns, gar-dens or flower beds, where they lay eggsand provision the young larvae with para-lyzed cicadas. This nesting activity maydamage lawns or vegetable gardens.Control is rarely warranted for this other-wise beneficial insect. When control is

necessary, sprinkle about 1 tablespoon of carbaryldust into the gallery hole and tamp the entrance shut.

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Baldfaced hornet(Dolichovespula maculata)and nest on side of house.(Photo – Garland McIlveen)

C ricket Hunter WaspsCricket hunter wasps in the genus Liris are occa-

sional indoor pests in Texas. These solitary wasps are1/2 - 5/8 inches long and dull black with dusky-coloredwings. They spend much of their time searching forcrickets, which they attempt to sting, capture andtransport live to an underground hole. After a crickethas been collected, the female lays a single egg on thevictim. The larva that hatches eventually developsinto an adult wasp.

Little is known about these insects. In urban areas,cricket-hunter wasps may nest under or in the wallsof buildings. When this happens, the offspring of nest-building females may emerge into indoor rooms.Because numerous crickets may be provisioned with-in a wall void as described above, few or many waspsmay emerge indoors. In one case, more than 100wasps were counted from a single bathroom, appar-ently emerging from a slab opening under a bathtub.

Cricket-hunter wasps are seen most commonlyindoors during warm weather spells in the winter orearly spring. Infestations can be persistent and annoy-ing. Though not normally aggressive, they can sting ifprovoked.

The best solution is prevention. Fill any holes orcracks in soil that might lead under the home. Sealopenings, such as weep holes, that might provideaccess to wall voids. Ventilation weep holes should bescreened rather than caulked. Other cracks and gapsin walls should be sealed with expanding foam, mor-tar or other appropriate material. In severe cases, wallvoids may be treated with pesticide aerosols or dusts;however, there is little evidence that this treatmentworks consistently. Adult wasps can be safely killedwith a fly swatter or captured and released outdoors.

Mud DaubersThese wasps build small, tube-like nests of mud

under eaves, in attics and under the roofs of storagebuildings. Adult mud daubers are 3/4 to 1 inch longand vary from dull black with bright yellow markingsto blackish or iridescent blue-black. They have longer,more slender waists than most other wasps. As theydevelop in the mud tubes, young larvae are generallyfed spiders, including the poisonous brown recluse.

Control. Since females do not defend their nests,mud daubers structures can simply be removed by

hand with a putty knife.Mud dauberscan also be con-trolled by treat-ing the nestwith a labeledinsecticide. Even wheninsecticides areused, it is agood idea toremove the nestto prevent otherinsects frombeing attractedto it.

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Cicada killer wasp (Sphecius speciosus). (Photo – Mike E. Merchant)

Mud dauber (Chalybion californicum) on next.(Photo – Garland McIlveen)

Liris wasp. (Photo – Mike E. Merchant)

Tips for Pro fessionalsBecause of the hazards and difficulty applying

insecticides to some nest sites, wasp control is usuallybest left for professionals. In difficult wasp control sit-uations, pest management professionals shouldobserve the following tips:

■ Provide protective coveralls and bee veils to allworkers attempting control of bees, hornets andyellowjackets. These articles can be purchasedthrough beekeeper supply houses or over theInternet. Employees with a known history ofallergic reactions to bee stings should not under-take such jobs.

■ Under no circumstances should employees climbladders during control efforts without protectivegear and prior experience with stinging insects.

■ The most effective delivery systems for difficult-to-reach yellowjacket or bee nests includeaerosol generators and pump-type or powerdusters. Effective insecticidal dusts includedeltamethrin and cyfluthrin. Addition of silicagel dusts (e.g., Drione®) may enhance nest pene-tration and, hence, the speed of control.Effective ULV aerosol insecticides include syner-gized pyrethrins and pyrethroid insecticides suchas resmethrin.

■ Portable foam generating machines can be usedto treat underground voids and voids in walls.Foams assist in ensuring that voids are complete-ly and uniformly treated. Be sure to follow foamand insecticide label directions carefully to avoidcausing electrical shorts in walls.

■ Entrances to yellowjacket nests in structurewalls generally should not be sealed until thecolony has been eliminated. If nests are not com-pletely eliminated, wasps may force their wayinto homes, looking for a new point of exit fromthe nest.

■ In addition to conventional residual insecticides,paper wasp and other exposed wasp nests can betreated safely with pressurized sprays of insecti-cide soaps, peppermint oil, eugenol and othernatural insecticides. These insecticides mostcommonly work as contact killing agents only,so re-treatment may be needed. Peppermint andother plant-derived oils may be considered asGreen List products for purposes of use on Texaspublic school grounds. For the latest in informa-tion on products approved for use in Texasschools, visit the website athttp://schoolipm.tamu.edu or call toll free 877-747-6872. Additional information is alsoavailable at http://insects.tamu.edu.

■ Control of bees is more complicated than waspcontrol and generally requires nest removal. For more information about control of honey bee nests in and around homes, see Extensionpublication L-1791, available online at http://tcebookstore.org.

Insecticide label clearances are subject to changeand changes may have occurred since this publica-tion was printed. The pesticide user is alwaysresponsible for the effects of pesticides on his ownproperty, as well as problems caused by drift fromhis property to that of others.

ALWAYS READ AND FOLLOW CAREFULLY THEINSTRUCTIONS ON THE PESTICIDE LABEL