Editor’s Note: The following article is an excerpt from the forth coming PCT book “Field Guide to Stinging & Biting Arthropods” written by Stoy Hedges and Dr. Gerald S. Wegner. For more information on PCT-published books, head here.
Paper wasps in the United States consist of two genera of social wasps in the family Vespidae — Polistes and Mischocyttarus. Polistes spp. and Mischocyttarus spp. (long-waisted paper wasps) can be distinguished from most other vespid wasps (i.e. hornets, yellowjackets and pollen wasps) by the longer, tapered basal gastral (second abdominal) segment, although there may be some confusion with similar looking potter and mason wasps (subfamily Eumeninae). The long-waisted paper wasps (Mischocyttarus spp.) have an especially long basal gastral segment of the abdomen. Also, paper wasps have noticeably longer second (mesothoracic) and third (metathoracic) pairs of legs, compared to other vespid wasps.
A variety of paper wasp species are found around the U.S. A pest professional anywhere in the United States will likely encounter at least several species in their area. For example, one of the authors regularly sees four species in and around his house in West Tennessee. Keep in mind that some species of paper wasps may vary in color form from nest to nest.
Most paper wasps are about 1 inch (25 mm) in length but some species are smaller. The largest North American species is Polistes annularis, which is more than 1 inch in length. This species is usually found on buildings located near bodies of water.
Noticeable differences exist between female and male paper wasps. This sexual dimorphism is more apparent in darker species than in lighter, brightly colored species. Female paper wasps have shorter antennae with slightly curved antennal pedicels. Males have an extra segment in their longer antennae with recurved tips. Also, females tend to have darker faces and abdominal sternites (undersides) than males. Males have more yellow on the face and more extensive yellow markings on the underside of the abdomen. Males are produced and make their appearance late in the colony growth season, which corresponds to late summer in temperate climates. It is not uncommon to observe males clustered on surfaces near their nests in late summer and fall. Males mate with females and visit flowers for sustenance but are not adapted to survive cold winters.
Paper wasps are semi-social and native to North America. About 24 species of Polistes spp. occur in North America, north of Mexico, a few of which also occur in the Caribbean and Central America. The European paper wasp, Polistes dominula, was introduced to the U.S. in the 1970s. It was first identified in Massachusetts and was likely transported from Europe aboard cargo ships. P. dominula is yellow and black in coloration and somewhat resembles a yellowjacket.
The two or three species of Mischocyttarus (long-waisted) paper wasps occurring in North America north of Mexico are also found in Mexico. At least one species, M. mexicanus, likely originated from Central or South America.
Most paper wasp species form colonies of a few dozen to a couple hundred individuals. As with most social and semi-social species of bees and wasps, female (daughter) wasps are produced all season long while males are produced late in the nesting season. Nests in temperate regions are founded in May or early June, occupied for a single season, and do not survive the winter. The overwintered mated females (gynes) of the European paper wasp, Polistes dominula, are active and founding their nests earlier in the spring than other species.
After the dominant female (“queen”) and any auxiliaries finish rearing the first generation of daughter wasps, the subordinate females and daughter (worker) wasps seek vulnerable, soft-bodied insects and spiders to serve as larval sustenance. Foragers masticate (pre-chew) larval prey and feed the prepared bolus to hungry brood by trophallaxis.
In temperate zones young gynes leave the nest in late summer or fall and mate, often more than once, with males (drones) that are forcibly driven out of the colony. The drones and workers die as the weather turns colder. The young queens feed intensively to build up stores of fat for the winter. Mated gynes undergo diapause in a hibernaculum below ground or similar protected site.
Paper wasps play a minor role as pollinators of wild and cultivated plants as they feed on nectar. They have no specialized structures for carrying pollen from plant to plant but pollen does adhere to the sparse setae on their bodies.
Nesting Behavior. Paper wasps are sometimes called umbrella wasps due to the upside down paper nests they construct hanging from sheltered surfaces (i.e., under soffits) or inside structural voids.
Nests are founded by mated dominant females, which are the principal egg layers. Subordinate females (a.k.a. auxiliaries), which may begin in competition with dominant females, and daughter wasps, serving as workers, primarily forage and do not lay eggs. If the foundress female, which serves as “queen,” is removed from the nest, the second-most dominant female assumes the role of oviposition.
The seasonal nest size of paper wasps depends on the species and success of the occupants affected by local environmental conditions. The number of brood cells in a successful nest may vary from a few dozen to a few hundred. Large nests housing many dozens of workers can be encountered.
Nests are typically constructed in sheltered situations. In wooded areas, nests may be attached to tree branches or in tree holes. Favored nesting sites include: (1) undersides of large leaves, (2) underside of building porticos, overhangs, soffits and eaves, (3) behind window shutters, (4) beneath decking and handrails, (5) in open ends of uncapped pipes (i.e., rails of chain link fences and playground equipment, (6) in decorative mailbox casements, (7) inside bird houses undersides of bridges and overpasses, (8) underside of little-used patio umbrellas and grill hoods, and (9) bumpers and other features of little-used vehicles.
Paper wasps will build nests on both horizontal and vertical surfaces but almost always in areas sheltered, in part, from rainfall.
Certain species (i.e., Polistes carolina and P. rubiginosus) prefer concealed nests within structural voids such as those above soffits and eaves. A common structural nesting site are roof returns where one roof meets another. Such nests are a particular threat to workers such as roofers and painters. Void-nesting species will also locate nests within hose reels and gas grills, and electric boxes. The risk of stings are greater with these latter locations as people open the grill or electric box disturbing the wasps while being in close proximity to the nest.
Overwintering Behavior. In the fall, paper wasp queens (or gynes) leave the nest and mate, then search for protected sites to spend the winter. In nature, overwintering sites include tree holes and leaf litter. Heated buildings, however, are more attractive as nesting sites and paper wasp queens fly to sun-warmed walls, then enter through roof returns and soffits as wells other exterior openings.
The queens are known to release pheromones which can attract other queens to particular sites. In homes, dozens of queens may accumulate in attics, but in commercial buildings, hundreds of queens may become involved. As wasps approach tall buildings, updrafts along the sides of the structure carry the insects up, often to balconies far above the ground and even the roof. Queens enter through weep holes, under flashings and any exterior cracks and can work their way into false ceilings and then down into occupied areas. In one case of a hotel with an exterior glass elevator shaft, several thousand paper wasps, alive and dead, were found inside the elevator shaft. Queens can also accumulate on the roofs of tall buildings. In homes, chimneys often are harboring sites for paper wasp queens.
During periods of warm weather during winter and then in the spring, wasps in the attic or false ceilings become active and some find their way down into the rooms below. Several different species may be found side by side attracted to windows in an attic or windows in rooms.
Wasps in Attics. Because paper wasps commonly nest in voids behind roof returns and in soffits, on occasion, wasps will enter the attic and become disoriented. Such wasps are often attracted to light emitting through can lights or around ceiling vents or fixtures attached to the ceiling. One to a few wasps can then enter the rooms below and be encountered by the homeowner. Usually this is not a major concern but in some cases the wasp encounters are daily or involve many wasps being seen in living areas.
Effect of Stings or Bites on Humans. In general, paper wasps are less aggressive in defending their nests than are yellowjackets or hornets. Still, if the nest is disturbed, they will attack and sting. Paper wasp nests are commonly located in or near doorways, which can prompt stings when the door is opened or when people approach the door. Also, paper wasps are far more commonly encountered on buildings than other wasps, which also increases the potential for person-wasp encounters.
Vespid venom is variable among genera but generally have in common proteins that act as allergens and a variety of vasoactive amines and peptides. Paper wasp sting reactions involve immediate intense pain, but are usually accompanied by less swelling, redness and soreness at the sting site than stings of yellowjackets and hornets. This is due in part to the composition of the venom, and in part to the tendency of paper wasps to sting quickly and escape, thereby injecting less venom into victims than yellowjacket and hornet workers, which cling tenaciously to victims while prolonging the injection of venom.
Pharmaceutical companies process venom collected from live-frozen paper wasps for use in the treatment and desensitization (immunotherapy) of persons allergic to stings.
IMPORTANT: Pest professionals known to experience mild to severe reactions to wasp stings should avoid conducting wasp and bee control work. Pest professionals at high risk of severe sting reactions may be prescribed an EpiPen® (or equivalent) by their doctor. Such individuals should carry the EpiPen on their person at all times doing any pest control work during warm weather as a wasp or bee sting can occur at any time, even when bees and wasps are not the target pest.
Paper wasp species, which locate nests in exposed sites are easy to find and fairly straightforward to treat. Those species that prefer concealed nest sites can go unnoticed by homeowners and pest professionals unless one takes the time to stand still and observe for wasps entering and exiting through an exterior crack or hole. Usually such nests are associated with soffits or roof returns where one roof line attaches to a lower roof on a home.
Wearing Protective Gear. Typically, treatment of paper wasp nests does not require wearing a bee suit or other protective gear. A bee suit may be necessary if a pest professional must climb on a ladder to reach a nest located within a structural void like a roof return.
Timing of Treatments. Unlike yellowjackets and hornets where early morning or evening applications are recommended when most wasps are in the nest, paper wasps may be treated at any time during the day. Paper wasp nests are typically small with only a few dozen workers and residual treatments will kill wasps present during the treatment and also kill foraging workers that return to the nest site and contact residual deposits on surfaces.
Paper Wasp Nests on Exposed Surfaces. A number of aerosol wasp control products are available that allow the applicator to treat paper wasp nests at a distance of up to 15 feet or further. Water-based residual formulations may be labeled for direct treatment of paper wasp nests and are usually applied with a compressed air sprayer using a pinstream spray pattern.
When treating a paper wasp nest, avoid standing directly under the nest; instead stand off to the side. When wasps are contacted with the spray, they often fall or fly toward the ground and can land on a person. Stings can happen, especially if a wasp falls into an open collar on a shirt. A good practice to follow is to apply an initial short treatment of the nest, then walk a few feet away for a minute before returning to finish the application.
Aerosol wasp products that dispense as a foam are available that instantly cover the nest and the wasps. Foam-covered wasps drop to the ground or otherwise impede the wasps’ ability to fly but a few feet. Only a small amount of material is needed to treat the nest.
Nests located on soffits of two-story buildings may be treated using a wasp aerosol mounted on a “bee-pole” designed for applying aerosols to elevated sites.
When using a water-based product (i.e., SC, CS), apply to the wasps and nest, soaking it thoroughly, but avoid overapplication of treatment. This latter point is especially true if treatment of wasps nests located far above the ground must be attempted using a truck-mounted power sprayer to reach the nest.
Nest Removal — The nest should be knocked down, where possible, after treatment. For nests high above the ground, a paint scraper mounted on an extendable pole can be used to scrape off the nests. A file can be used to round the corners and edges of metal scrapers so they won't damage surfaces during nest removal; or plastic scrapers can be used.
Paper Wasp Nests in Voids. Once a void where paper wasps are nesting is located, it is easy enough to treat by injecting a residual dust or aerosol product. A dust formulation is recommended as it travels a further distance into the void especially if applied with a battery-powered duster like the Exacticide®. This is important when nests are located inside soffits or into attics where the nest may be several to many feet from the hole where wasps enter and exit the building.
Paper Wasps Entering Interior Rooms from Attics. Occasionally, a homeowner will report seeing wasps regularly inside during the summer, in the fall or spring. When seen inside during summer, a wasp nest in the attic is usually involved and the wasps are entering through can lights in the ceiling or through cracks around ceiling fixtures (i.e., lights, ceiling fans). In the spring and fall, the situation usually involves overwintering queens as described earlier in this chapter.
If a wasp nest is located within an attic, finding and treating the nest is the best course of action. Customers should be advised to seal cracks at the ceiling around light fixtures, vents and ceiling fans. Where can lights are involved, customers can purchase LED can light retrofit kits that effectively seal lights against pests entering through them from the attic. These kits are available at hardware stores and online retailers.
Paper Wasps Entering Interior Rooms from False Ceilings. In commercial buildings, paper wasps can enter spaces above false ceilings from exterior walls and then find their way into the rooms below. Where this situation is occurring with regularity (such as with overwintering queens), placing one or more insect light traps up in the false ceiling can attract and capture most of the wasps. Glueboard style ILTs are recommended.
With smaller commercial buildings of one or two stories, treatment of exterior cracks with a residual dust may be done to help kill wasps entering into the walls. The customer should be advised to seal as many cracks as possible in exterior walls to help stop future invasions.
With high-rise buildings, not much can be done to stop wasps entering walls on upper floors or accessing exterior balconies. With severe wasp issues seen inside, the customer may want to consider a contractor experienced with high-rise exterior work to seal as many exterior gaps as possible, including those beneath flashing.
Overwintering Queens. Structures that experience issues with overwintering paper wasp queens are likely to have the same problem from year to year. The best long term solution to paper wasp invasions is exclusion. Most of these efforts should be directed at the soffit area and roof line of the structure and where different types of building materials meet (i.e., wood meets brick).
One of the key areas where wasps enter is the gap that exists under the edge of the roofline where the fascia board meets the roof. The ease with which wasps and other pests can enter through this area is shown in. This gap can be covered over using a gutter apron — an L-shaped metal flashing that covers the gap from the fascia board to the roof subdeck and then down into the gutter.
Sealing other entry points with silicone sealant or material such as Xcluder® rodent fabric will help long-term to prevent overwintering paper wasp queen issues. Treating cracks with a residual dust product prior to sealing them is recommended.
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