TWO MOST-COMMON IN WYOMING DIFFER IN

Aerial yellowjacket more mellow, western yellowjacket just plain grouchy

Scott Schell he bold, contrasting color patterns on yellowjacket Twasps act as a warning to potential predators they pack a potent sting. The 11 species of yellowjacket wasps (subfamily , in the order ) in Wyoming all ex- hibit this warning, or more accurately, aposematic color pattern. Unlike honey workers, which can only sting once at the cost of their lives with barbed , yel- lowjacket females can sting repeatedly with their smooth stingers. will do so readily if physically as- saulted or in defense of their . Their color pattern is so effective at deterring preda- tors that defenseless species, such as the flower species (order Diptera, family Syrphidae) have evolved color patterns that closely mimic yellowjackets for pro- tection. Like honey , yellowjackets are an eusocial insect, which means related individuals work coopera- tively to produce the next generation. Yellowjackets, and their close relatives the paper wasps (subfamily ), use the original version of papier-mâché to construct their nests. The “paper” these wasps make consists of fibers they chew off plant stems and weathered wood mixed with their sticky saliva. The design and placement nests vary by species. As with many other insect pest species, proper iden- tification of the perpetrator and a working knowledge of Aerial Yellowjacket their life cycles can help you implement the best control methods.

FALL 2017 7 Western and Aerial Yellowjackets The two most common species of yellowjackets in Wyoming towns have different nesting preferences. The western yellowjacket ( pensylvanica) prefers to under- ground, frequently taking over and enlarging abandoned rodent bur- rows as their nests get bigger (Photo 1). They will also readily use crawl spaces and cavities in or under hu- man structures. Aerial yellowjackets Photo 1. The entrance to an underground yellowjacket nest by a brick wall ( arenaria) prefer the shows the soil removed by worker wasps as they excavate the cavity to expand shelter of overhangs such as the the paper nest. eaves of houses or under the branch- es of trees for their paper-covered nests (Photo 2). Knowing the life cycles of these yellowjacket species is a key to their control if they become pests. The life cycle of both is very similar. A new queen emerges from her natal nest in the late summer and mates with a male yellowjacket (males are produced in the summer for the sole purpose of mating with the new queens and then they die off). This of- ten occurs at congregations of wasps on hilltops within sight of the nests. Photo 2. The overhangs on buildings make great nest sites for aerial During mating, a new queen is able to yellowjackets. Their nest construction differs from the yellow and black store all the sperm she needs for the European paper by having a cover of paper over the larval cells. rest her life. She will then forage for food through late summer and seek a of daughters and a paper cover to dies while doing this, they all die. protected place to spend the winter protect them with a single entrance When the yellowjacket larvae are fully alone. Locations such as under loose at the bottom. A single fertilized egg grown, the queen caps the ’s cell bark on dead trees, in firewood piles, is put in each cell. The sex of her with paper. They pupate and undergo and in building attics are often used offspring is determined by the queen. metamorphosis into the adult winged as a hibernation refuge. If she releases some of the stored form. When these first daughters If a queen chooses her winter sperm, it fertilizes the egg and the emerge, they take over the work of quarters well and survives, she be- egg will develop into a female wasp. defending and expanding the nest, comes active again when the weather Unfertilized eggs, with only the genes foraging for food, and caring for the warms the following spring. The from their mother, develop into male subsequent offspring of their mother. young queen will forage for food and wasps. This ability to control the gen- The adult daughters are inhibited search for a suitable place to build der of offspring genetically is called from producing their own eggs by her nest and start her own colony. haplodiploidy. a pheromone scent emitted by the The new nest starts small and After the first eggs hatch, the queen. consists of a single tier of hexagonal queen has to forage to feed these paper cells for rearing the initial brood first few daughters herself. If she

8 BARNYARDS & BACKYARDS Their Habits nest. However, all yellowjacket spe- Aerial yellowjacket nests are cies only travel as far as needed to the most frequently noticed kind in find food. Wyoming, with their penchant for Unwelcome Outdoor Visitor putting gray-colored, paper-covered The western yellowjacket is also nests under the eaves of buildings. the species that most frequently in- None of the yellowjacket species terrupts outdoor dining at picnics and reuse a nest from the previous year, was found to inflict 9 out of 10 insect but a good location may attract a new stings people suffer according to a nest every year. Photo 3. The pattern of black markings study conducted in Colorado. Despite Aerial yellowjackets are primarily on the head and top of the abdomen being a predator on some predators of other insects and prefer differs between species of yellowjack- considered garden plant pests, the prey such as caterpillars. The prey are ets. This drawing illustrates the typical negatives of western yellowjackets, chewed into a “baby food” consisten- markings on a worker western yel- such as attacks on hives, cy and fed to the developing larvae. lowjacket. From “The Yellowjackets of feeding on ripening fruits in orchards Western yellowjackets are fre- and gardens, scavenging at picnics quent scavengers of meat from road- America North of Mexico.” due to their attraction to people food, killed . They also like to forage Because the aerial yellowjacket and drinking from both fermented in uncovered human garbage and so closely resembles the more pes- and sweet beverage containers, can chew the remains of dead insects tiferous ground-dwelling western outweigh their benefits. off the front of cars. They can also yellowjacket, probably more cans of They readily sting in defense of be beneficial as opportunistic preda- “wasp” spray is expended on their their underground nest entrances. tors of plant-feeding insects. Western exposed nests than any other spe- These behaviors make the species yellowjacket adults will also feed on cies in Wyoming. This usually doesn’t deserving of control around homes sweets, such as ripening fruit, for solve people’s problems with yel- and farms. energy. All yellowjacket colonies, if lowjackets. Western yellowjackets The best way to reduce western successful, continue to expand with are much more likely to be the pest yellowjacket populations around a more workers being produced until in your yard. One study found that home is to start trapping early in the the queen starts to produce the next worker western yellowjackets would spring to catch the new queens and/or generation of queens and the males forage as far as 1,100 feet from their the first daughters to eliminate or stunt to mate with them. new colonies. Commercial traps baited In studies conducted in with heptyl butyrate, which smells like Washington State, the populations of rotting fruit, are very effective against worker yellowjackets per nest varied the western yellowjacket. Other bait widely with species and the year’s The USDA Agriculture ingredients may enhance the trap particular environmental conditions, Handbook Number 552 catches, but heptyl butyrate used alone especially the early spring weather. “The Yellowjackets of is very effective for catching western Western yellowjacket colonies were yellowjackets. found to have anywhere from 900 to America North of Mexico” Later in the spring and summer, almost 4,000 workers by late summer is a comprehensive trea- refresh the bait and move the traps to in areas with lots of food resources. tise on these fascinating the outer edge of your yard to inter- Aerial yellowjacket colonies were insects and is available for cept foraging western yellowjackets similar in size. After the production of coming from nests from beyond your males and new queens, nest expan- download at yard. The pattern of black on yellow sion ceases and the first hard frost is bit.ly/wyoyellowjackets on the head and abdomen can be the end of life for the old queen and used to distinguish the western yel- her worker daughters. lowjacket (Photo 3).

University of Wyoming Extension assistant entomologist Scott Schell risks life and limb (we’re exaggerating a LITTLE) to bring useful insect information to Cowboy State residents. He can be reached at (307) 766-2508 or at [email protected].

FALL 2017 9