There are over 2500 species of wasps in North America. The best known are the brightly-coloured ones that buzz around us and sting. But only 50 species sting. The vast majority mind their own business and are rarely noticed.
Most wasps are carnivorous and eat insects. As a result, they’re extremely beneficial as nearly every pest insect is preyed on by a wasp species, either as food or as host for its parasitic larvae. Wasps also need to drink nectar or eat pollen to stay healthy and will pollinate plants while searching for prey or eating. Some studies have shown that wasps become primary pollinators if bees are absent.
Unlike bees, wasps have a pointed abdomen and a narrow waist separating the abdomen from the thorax. Bees are usually hairy, while wasps are less so. While some wasps are social and share a common home, the vast majority are solitary, laying their eggs in individual nests.
Social Wasps
Hornets, yellowjackets, and paper wasps maintain a communal nest and share responsibility for building the nest, finding food, and raising the young. They defend their nest against perceived threats.
Yellowjackets, with their distinctive yellow and black stripes, are one of the most visible wasps in our gardens and one of the most aggressive. Paper wasps aren’t as defensive and may give a warning bump or stand up and flare their wings before stinging you. There are easy things you can do to prevent wasp stings as outlined at the end of this article (Preventing Wasp Stings).
Social wasps build their nests in sheltered places – the corner of a shed, under building eaves or tree branches, or on the ground in an abandoned burrow. While most bees die over the winter, mated queen bees stay alive by sheltering under bark or in a crack of a building. Early in the spring, a wasp queen works alone to begin building a nest. Using her strong jaws, the queen tears strips of wood off trees, fences, or outdoor furniture. Using the saliva in her mouth to break down the wood fiber and create a soft paper pulp, she then constructs hexagonal brood cells for future larvae. Once the nest is established, the worker bees take on responsibility for enlarging the nest by adding additional layers of cells. Yellowjackets enclose the brood cells in a paper envelope, while paper wasps leave the cells exposed.
Solitary Wasps
Solitary wasps build individual nests with one female wasp in each nest. Most nest on or in the ground. Some use mud to build their nests while others nest in cavities such as a hollow plant stem or a hole. Several wasps may build their nests in the same area. The adults feed on plant nectar but prey on insects or spiders to feed their young.
Solitary wasps aren’t aggressive and will only sting when handled roughly. Potter wasps shape mud into nests shaped like small clay pots. Each pot is attached individually to a sheltered area on a wall, twig, or fence. Black and yellow mud daubers collect moist mud balls to create their cigar-shaped nests. Each nest contains two or three cells where the female lays an egg and food for the larvae to eat when they hatch. The cells are sealed to keep out predators and to protect the larvae from the weather.
Pest Control & Pollination
Wasp larvae require a high-protein diet. Female social wasps use their ovipositor (egg-laying tube) to inject venom into spiders and insects to paralyze them before either chewing them up or dragging them back whole to feed their young.
Solitary wasps will either lay their eggs directly into their host prey (e.g. a tomato hornworm) or store paralyzed insects in the nest cell along with the egg. Black and yellow mud dauber wasps inject paralytic venom into a spider’s nerve center before dragging it back to their nest. The mud dauber will enclose up to 25 paralyzed spiders in a clay chamber along with an egg. The spiders will be eaten, one by one, by the wasp larva.
Once fully developed, adult wasps switch to a largely carbohydrate diet and become accidental pollinators as they move from one flower to another, sipping the nectar and transferring pollen from one plant to the next.
Preventing Wasp Stings
You walk into your garden shed and a wasp stings you. It seems totally uncalled for and you’re angry. Think about it from the wasp’s perspective and you’ll realize that you’d invaded its home territory. Here are some tips for sharing your outdoor space with wasps without running into problems.
Inspect your yard, bushes, and outbuildings in early summer for wasp activity or nests under construction. It will be easier to remove a single queen bee than a full-sized nest later in the season.
Seal cracks and crevices in your home to prevent wasps from nesting indoors.
Don’t leave high-protein (e.g. pet food) or sugary food (picnic leftovers or drinks) in the open and uncovered. When eating outdoors, you may want to place a small saucer of food a good distance away from your table to keep wasps occupied away from people.
Nests in bushes or on the ground are often difficult to spot. Watch for streams of wasps coming and going from specific locations and do a quick check before using a lawnmower or other yard tools whose vibrations may irritate wasps and cause them to sting. Pay attention to where you place your feet when walking barefoot in grassy areas.
Take extra precautions in late summer or early fall. Wasp colonies will have stopped breeding new workers and the remaining workers will be searching for sugary foods and may come into contact with humans.
Further Information
Endless Forms: The Secret World of Wasps, Seirian Sumner
Wasps: The Astonishing Diversity of a Misunderstood Insect, Eric R. Eaton
How We Can Stop Hating Wasps [Bug Eric]
Wasps and Their Role as a Beneficial Insect and Pollinator [Penn State Extension]
Wasps [Wikipedia]
Social Wasps: Yellowjackets, Hornets, and Paper Wasps [University of Maryland Extension]
Solitary Wasps [University of Minnesota Extension]
Six Unexpected Pollinators [EcoFriendly West]
Solitary Bees are First-Class Pollinators [EcoFriendly West]
Photo credit: Yellow-legged Mud Dauber https://www.flickr.com/photos/apmckinlay/51333335388
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