Hornets and Yellowjackets

Hornets and yellowjackets spend the summer searching plants for insects to capture and carry back to the nest as food for developing larvae. Vision and learning are key parts of their success in locating prey and returning to productive sites. Most tend to stay within a few hundred feet of their nests and are not aggressive. That can change quickly; movements toward the nest may provoke an aggressive defense. Hornets and yellowjackets can sting repeatedly and often attack as a group if disturbed. Their sharp stingers produce a painful sensation that may intensify after their venom is injected. Severe reactions can occur in sensitive people or those who are stung many times.

European Hornets

European hornets (or giant hornets) are 1½-inch-long yellow and brown insects with dark wings (Figure 1). They build enclosed paper nests in hollow trees, barns, attics, and wall voids. An average nest will have 200 to 400 workers by late summer. These large hornets usually only sting when threatened, but they will defend their nests vigorously. They fly at night and are attracted to lights, so they may crash into windows after dark.

Figure 1. European hornet (top left), enclosed nest in storage room (right), paper cells where larvae are reared (lower left). (Photos: Lee Townsend, UK)

Figure 1. European hornet (top left), enclosed nest in storage room (right), paper cells where larvae are reared (lower left). (Photos: Lee Townsend, UK)

European hornet workers and males die in the fall, leaving an empty nest. Fertilized females survive the winter under the protective covering of loose bark or other sheltered places. They will found new colonies in the spring. European hornets capture large insects – grasshoppers, flies, bees, etc., to chew and feed to their larvae. Some will girdle twigs and branches of lilac, birch, ash, and other species. Sap collected from the wounds provides them with energy and water.

Bald-faced Hornets

The bald-faced hornet is ½ to ¾ inch long with distinct black and white markings; its wings are dark (Figure 2).

Figure 2. Bald-faced hornet. (Photo: Lee Townsend, UK)

Figure 2. Bald-faced hornet. (Photo: Lee Townsend, UK)

Also called the aerial yellowjacket, this species builds paper-covered football-shaped nests that often hang from tree limbs (Figure 3). Often the nests are high enough to minimize encounters with people. Bald-faced hornets are not aggressive while searching for insects to feed their young, but they will defend their nest.

Figure 3. Bald-faced hornet nest (Photo: Lee Townsend, UK)

Figure 3. Bald-faced hornet nest (Photo: Lee Townsend, UK)

Peak colony size is usually between 100 and 300. Workers search for flies, caterpillars, and spiders to feed to their developing larvae. All individuals except fertilized queens die in fall. Surviving queens develop a new nest in spring.

Yellowjackets

Yellowjackets (Figure 4) build paper nests below ground, often in abandoned chipmunk burrows or other tunnels made by small mammals. A colony may contain 800 to 1,000 workers. Like the other species, fertilized queens survive winter in sheltered places and establish colonies in spring. Yellowjackets capture insects to feed their developing larvae but also will collect meat from carcasses or scraps.

Figure 4.  Yellowjacket (Photo: Lee Townsend, UK)

Figure 4. Yellowjacket (Photo: Lee Townsend, UK)

Wasp and Hornet Management

  • Do not seal openings to active nests.
  • Unless a nest poses a serious threat, leave it alone and avoid the area until late fall.
  • All nest inhabitants, except fertilized queens that have left for protected overwintering sites, will die in the fall. Then, it will be safe to remove nests in attics or wall voids and to plug entryways. While old nests are not reused, openings may be discovered by a searching queen and a new nest may be built.
  • If nest removal is required, hire a professional with the equipment and experience to do the job safely. Serious injuries can occur while treating an active nest.
  • Know which wasp or hornet is causing the problem. Differences in nesting site, colony size, and food preferences may call for different strategies.
  • Yellowjackets are attracted to soft drinks, some meats, candy, fruit, and ice cream. Keep these items covered, especially soft drink cans and cups.
  • Outdoor trashcans are very attractive to yellowjackets. Use plastic can liners, tight fitting lids, and remove trash frequently. Yellowjackets return repeatedly to a good food source from nests more than 1,000 feet away.

 

By Lee Townsend, Extension Entomologist

Posted in Human Pests