Volume 28 Issue 2, Spring 2023
by Cliff Fairweather
Wasps need some love. They rank pretty low on most people’s list of favorite insects for just one reason: they sting. Actually, only a small fraction of wasp species pose a serious stinging threat to humans. Most don’t even have stingers, and most of those that do rarely sting people. As a recovered spheksophobe (someone with a fear of wasps), I have found the more I know about wasps, the less I fear and the more I appreciate them.
Wasps are members of the insect order Hymenoptera, with over 150,000 currently described species, though entomologists believe there are actually many times that number. This includes primitive wasps (sawflies, wood wasps, and horntails), parasitoid wasps (a parasitoid is a parasite that kills its host), a few other minor groups, and the stinging wasps.
The stinging wasps, or aculeates, are the only wasps capable of stinging. (Bees and ants are also part of this group, but they get good press and won’t be covered here.) The stinger is located at the end of the abdomen and is usually kept concealed until the wasp is ready to sting. It is actually an ovipositor (egg-laying organ) modified through evolution to deliver venom. Wasps now lay their eggs through another opening. Unlike honeybees, wasps can sting multiple times. Male wasps lack ovipositors, so they can’t sting. The coloring of most stinging wasps are aposematic (warning) colors, usually contrasting black and yellow, white, or red.
The majority of stinging wasps are solitary, meaning they don’t form colonies with a queen and workers. Examples include cicada killers, mud daubers, digger wasps, and mason wasps. Very few defend their nests, and they pose relatively little stinging risk if left alone. Each female produces her own offspring asexually, giving birth only to daughters, without fertilization; and she spends most of her time hunting for prey to feed them, and constructing burrows or other shelters to protect them. They sting primarily to capture prey and only sting people in self-defense. Stinging large animals is risky, and if a female dies in the process, her genetic line dies with her.
The social wasps — including in our region paper wasps, yellowjackets, and hornets — account for the vast majority of stings, even though they constitute a tiny portion of wasp species, about 800 worldwide. They form colonies with a caste structure consisting of a queen and sterile or otherwise non-reproductive female workers, who are all sisters. The queen, who mated during the previous late-summer, starts a colony in the spring by constructing a nest out of paper that she makes by mixing wood fibers with saliva.
Once the queen has raised some daughters, they take over constructing and maintaining the nest, tending the young, and foraging for prey. They also defend the colony. Their genetic future is in the queen’s offspring, so they will risk their lives in defense of her young. The queen devotes her time to producing more workers until late summer, when she starts producing fertile males and females. These then disperse to find mates, and the mated females find secure places to hibernate through the winter, sometimes including inside houses. They might appear flying around inside in the late winter or early spring. The old queen stops laying eggs and dies soon after, followed by the workers and the males. The old nest is not reused.
The social wasps in our region include paper wasps (Polistes species), aerial yellowjackets (Dolichovespula species), ground yellowjackets (Vespula species), and European Hornets (Vespa crabro).
Paper wasps are about a half-inch long, have long legs that trail behind them in flight, and vary in color. They construct small open-comb nests that resemble little upside-down umbrellas suspended from surfaces such as tree branches, overhanging rocks, or window frames. The combs are composed of hexagonal paper cells that house eggs, larvae, and pupae. Although touchy close to the nest, paper wasps are less aggressive than other social wasps and their colonies are much smaller, usually fewer than 100 individuals.
Aerial and ground yellowjackets are about a half-inch long, have short legs, and are yellow and black or white and black. They construct large nests with paper envelopes that enclose and insulate the combs. Bald-faced Hornets, a common species of yellowjacket, despite the name and black and white coloration, usually place their large gray egg-shaped nests in trees or shrubs. These can be easily seen in winter. Ground-nesting yellowjackets often build nests in old rodent burrows. Yellowjacket colonies can number into the hundreds or even thousands, and their nests are defended vigorously.
European Hornets are an introduced species and have become fairly common. The workers are just under an inch long and have red and yellow on their heads, and yellow and brown abdominal stripes. They frequently nest in hollow trees but sometimes nest underground or in human structures. Colony size usually ranges from 200 to 400 individuals. Like yellowjackets, they can be very aggressive around the nest.
Yellowjackets and hornets often become troublesome in late summer. Their numbers have grown all season, their jobs are done, and their food supply is running out. Because of their narrow wasp-waist, adult wasps are restricted to a liquid diet, mostly flower nectar and a sugary substance produced by the larvae. Both of these sources are in sharp decline as summer ends, with flowers waning and the queen no longer producing larvae. This leaves thousands of hungry unemployed workers aggressively seeking food. Picnic tables laden with sweet drinks and desserts, fresh fruit, cooked meat, and other wasp-attracting delicacies set the stage for conflict … and the wasps come armed!
Getting stung is a risk of being outdoors, but there are ways to reduce that risk:
- Avoid wearing floral-scented perfumes, cologne, hairspray, or similar products that might attract wasps.
- When eating outside, keep food and drinks covered.
- Don’t kill or swat at wasps as this could cause them to release alarm pheromones (scents) that call their sisters to attack.
- Remember that peak social wasp populations unfortunately coincide with the peak late-summer picnic season.
Keeping your distance from wasp nests is an obvious safety measure if you know where the nest is. Watch for large numbers of insects flying in and out of a small area, particularly coming out of the ground. Should you find yourself close to a nest by accident, don’t panic. Calmly and slowly walk away. Breathe slowly, as wasps can detect carbon dioxide from your breath. If you disturb a nest or are stung near one, stay calm, move quickly away, and warn others nearby. Flailing at the wasps will only aggravate them further and cause them to emit alarm pheromones.
If you are stung, wash the area around the sting and apply ice or a cold pack. Over-the-counter sting remedies and pain relievers can also help. Watch for signs of severe allergic reaction (anaphylaxis), such as shortness of breath, rapid heartbeat, extensive hives, or tightness in the throat or chest. This can be life-threatening. If you have been prescribed an epinephrine auto-injector, use it, or else seek emergency medical help. Otherwise, the itch and swelling from a sting should fade in a few days.
Beneficial Insects With Important Roles
Wasps provide valuable ecosystem services, especially when it comes to regulating populations of other insects, including many agricultural and garden pests. In natural ecosystems, wasps are particularly important in providing a check on herbivorous insects. According to North Carolina State University, for example, a small colony of 200 yellowjackets can consume 5,000 caterpillars, mostly moths, in a summer.
Wasps provide a food source for other animals. Many bird species feed on wasps, protected from stings by their tough bills. Some mammals, such as skunks, bears, raccoons, and opossums, raid social wasp nests for the fatty, nutritious larvae and pupae. Lizards, toads, frogs, and salamanders are also among the connoisseurs of wasps. In parts of Asia and Latin America, people eat wasps in both their immature and adult forms.
The role of wasps as pollinators is often overlooked. They don’t have the adaptations of bees for pollen collection and transport, such as dense, branched body hairs, but their sheer numbers and dependence on nectar as a food source mean they visit lots of flowers. At least some of those visits will result in successful pollination.
Wasps Need Our Help!
Human activities pose a significant threat to wasps through habitat destruction and fragmentation, pesticide use, and climate change. Wasps with specialized habitat needs are particularly vulnerable. We can help by creating a little wasp habitat in our yards and gardens. Reducing or eliminating pesticide use is a great first step.
If you garden with native plants, you’re already helping. Wasps have short tongues, so include some plants with large clusters of small, shallow flowers such as mountain mints, asters, goldenrods, and milkweeds. Provide some shelter for overwintering wasps by leaving plant stems in place over the winter, along with lots of leaf litter. Leaving soil undisturbed protects the nests of many solitary wasps and benefits native bees as well.
Wasps, even social species, pose little threat when they are busy nectaring on flowers, so don’t be afraid of them visiting your garden. Show them a little love in your yard and they’ll return it with free pest control and pollination services and some beautiful and interesting insects to observe.
Cliff Fairweather is a local naturalist.