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Auburn, Alabama -- Fall is the peak season for yellow jackets and hornets in Alabama. Many people encounter and even experience painful stings from these wasps during outdoor activities.

Yellow jackets are mostly black-and-yellow wasps. Hornets can be black and while like the bald-faced hornet, or may have a red color background instead of black. Hornets typically have relatively large top margin of the head and rounded segment of the abdomen. Paper wasps are typically the members of Polistinae.

 

Yellow jacket (left), hornet (right) and paper wasp (bottom) – Images credit to Bugwood, InsectImages.org

All of them make nests of paper-like material containing chewed word fragments and saliva secretions. Most yellow jacket species nest underground using existing hollows, but some may nest aboveground in buildings, in tree cavities or structural voids. Hornets build nests by chewing wood to make a papery pulp, attached to tree or shrub branches or under building eaves. Their nests have paper combs with surrounding envelope. Paper wasps, also called umbrella wasps, usually construct water-resistant nests with open combs with not surrounding envelope. The nests usually are exposed in human-inhabited, sheltered areas, attached to wood on the underside of porch decks, eaves, or other overhangs of a house and in dark cavities.

Yellow jackets and hornets are very aggressive and their stings are very painful to humans. Paper wasps are not as aggressive as yellow jackets and hornets, but they do attack when they feel being threatened.

By fall, yellow jackets, hornets, and paper wasps reach maximum size of family members and peak period in activities. The cycle begins with a few mated overwintered females who start new nests from scratch early spring and become foundress queens. The new nests may contain a dozen developmental cells and remain relatively calm, often unnoticed. By fall, yellow jacket nests reach maximum size, typically contain 300 to 120,000 developmental cells depending on the species and environmental conditions. In south Alabama, large perennial colonies are maintained by some species and are ruled by multiple queens, tended by thousands of workers and contain millions of cells.

Most of the summer, yellow jackets are predators and feed on other insects. However in the fall, they diet changes to preferably sugary concoctions and they are mostly attracted to rotting fruit and tree sap, human beverages and sweet food, fruit juice, and the likes. They labor long hours to collect enough food to feed and maintain the colony overwinter.

Residents can deter wasps by eliminating food sources such as open garbage cans that providd food and moisture.  Prevent wasp stings by staying clear of areas that will attract the stinging wasps, including fruit orchards, flower-beds, picnic areas, outdoor restaurant seating and backyard barbecues.

Treatment should be performed late at night after all the wasps are resting in the nest. Identify the nest opening during the daytime so you can direct your treatment after dark.

The most useful tool for managing yellow jackets is arguably, a dust applicator directly to their nests. Hand dusters and air dusters are the more common applicators. These should be operated by a pest control professional who wears protective garments.

The advantage of using a dust formulation is that the dust can be carried by air deep into cavities and voids of wasp nests. The dust particles remain on the concealed surfaces, awaiting contact with foraging yellow jackets, which, in turn, contaminate other nest mates. Using wettable powder insecticides in surface-treating yellow jacket nests can accelerate the colony-elimination process. This permits same-day nest removal.

Aerosol and mist insecticides, such as pyrethirins and other botanical extracts, should be applied to nest cavities after dark when nest members are contained within the treatment zone. They can also be used during the daytime, provided you do not stand directly under the nests suing the treatment. One advantage of these formulations is that they can be sprayed as far as 20 feet. Most aerosol-based sprays cause wasps and hornets to drop instantly. After treatment, wait a few days to ensure that the colony is destroyed, then scrape or knock down the nest.

Although it is necessary to close off multiple entry points of wasps from structural voids to the living and work species, homeowners should never caulk close an exterior entrance to an active yellow jacket nest in a structure. This action only alarms the trapped wasps and causes them to seek out alternative escape routes to the outdoors.

Unlike honey bees, all female and worker wasps and hornets can sting repeatedly. They don't die after stinging because their stingers are not barbed and are not pulled out of their bodies.  With occasional stings comes the likelihood of increased sensitivity to venom. Be cautious of small areas bare of vegetation because they could be ground nests of yellow jackets.

Xing Ping Hu 

Professor/Entomology Specialist, ACES




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