Wasps and Hornets: Unlikely Allies

More than just pollinators, wasps and hornets are actually beneficial insects.

Wasp on a bright flower

Wasps are beneficial bugs in the garden, because they are predatory insects.

Photo by iStockphoto.com/johnandersonphoto

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Many people treat their gardens and backyards like a battlefield, waging war on anything they consider pests. Diseases, weeds, animals and insects all find themselves in the crosshairs. Until recently, the standard tactic was a “nuke ‘em all” approach of chemical warfare, especially where insects are concerned. Times and attitudes are changing, as gardeners have come to realize dead bugs aren’t necessarily the only good bugs. New strategies include insect-friendly practices like crop rotation, companion plants, buffer zones, and beneficial insect releases.

But one insect ally still can’t get a fair break, thanks to a mostly undeserved reputation for having a bad temper. As a friend of mine noted, no one has ever been described as “happy-go-lucky as a hornet.” For that matter, this may be the only time you’ll ever read the phrase “perky as a paper wasp.”

For the most part, people need not fear these underappreciated beneficial insects. That is, assuming you don’t have an allergy to their venom, and as long as you’re not throwing rocks at their nest. Venom allergies can be life threatening, so those allergic to a wasp sting get a pass on “live and let live” for nests in bad locations. But unless the nest is near a high-traffic area, there’s no reason to mess with it.

Wasps and hornets don’t go out of their way to pick a fight, regardless of popular opinion. They will, however, defend their nest vigorously if they feel it is threatened. That being said, you’re fine as long as you stay away. How far is far enough? For paper wasps, that means no closer than 4 or 5 feet from the nest, and 10 to 15 feet for a hornet’s nest. Yellow jackets will get excited if you step on their nest entrance or approach it with a lawnmower.

Wasps and hornets belong in the order Hymenoptera, along with bees and ants. It’s a big group, with some 150,000 species known worldwide. Most gardeners recognize and value the efforts of solitary parasite wasps, such as braconid wasps, feeding on tomato hornworm caterpillars. Most tomato growers at one point or another have seen a tomato hornworm, covered by and being eaten by pupating larva of braconid wasps, a cocoon resembling a grain of rice. However, this article is concerned not with solitary wasps, but colonial wasps, particularly members of two genera: Polistes (paper wasps) and Dolichovespula (hornets).

A little trivia about Dolichovespula: They aren’t true hornets; they’re aerial nesting yellow jackets. There is only one true hornet in North America, an introduced species that looks like a giant yellow jacket. Some things are just never simple.

Hornets and paper wasps build their nests out of a grey papery material consisting of chewed, pulped wood fiber and saliva. Paper wasps build a single layer of cells resembling honeycomb in a sheltered location. Favorite spots include roof overhangs, abandoned birdhouses, and inside swing-set pipe frames. Hornets build multilevel nests enclosed in a paper shell in heavy brush or tree branches, often high in the air. Their nests can reach the size of a football or even bigger. Ground-building yellow jackets will commandeer abandoned mouse burrows or similar cavities for their galleries.

Benefits for the brave

I know what you’re thinking: Why on earth would I want wasps hanging around in the first place? Probably the first thing you may think of is pollination, and it’s true, wasps will occasionally visit flowers, gathering nectar for a quick pick-me-up. That being said, wasps and hornets don’t do much pollinating. The real value to having them in the garden is their predatory nature. They hunt down and consume impressive numbers of insect prey and their eggs, especially pest caterpillars such as cabbageworms, tomato hornworms, tent caterpillars, and corn earworms. Adults will feed it to their brood. Tyler B. Corey, author of “Modeling the Impact of an Exotic Invasive on Community Structure,” estimates that a paper wasp colony can consume up to a 1,000 caterpillars in a season, depending on the size of the colony. Most nests average closer to 600 caterpillars. That’s still a lot of cabbage loopers.

Remember, a hornet nest can contain six times as many mouths to feed. Most wasps and hornets will forage in a range of about 130 yards from the nest, meaning you don’t need to be anywhere near the nest to gain the benefits in your garden.

Garden guests

Hosting a wasp or hornet colony is really simple; all they need is some shelter, water and building material. They will sometimes get themselves in trouble by chewing on wounds in the bark of a prized lilac, but will normally be content to get their wood from untreated wood exposed to the elements. The split rail fence in my backyard is a favorite hangout for both wasps and hornets.

Supplying water is as easy as maintaining a birdbath. Wasps and hornets also frequent mud puddles, fishponds, and swimming pools for a drink, and often rely on morning dews and rain showers.

Shelter is where you will make or break your working relationship with wasps and hornets. While there is no foolproof way to get them to nest where you want them to build, you can encourage paper wasps by offering them a nesting box set in an out-of-the-way spot. An old birdhouse with the front or bottom panel removed, or even just a bottomless box made of scrap wood, hung in a remote spot near your garden will serve the purpose. If you’re feeling especially generous, cover the entrance with chicken wire to protect the nest from birds and other predators.

Hornets, and most wasps, will pick a new location to build their nests each season, avoiding old nests and anything that looks like a nest. There is always an exception, of course, and that is the European paper wasp (Polistes dominula). This rule breaker often nests beside last year’s nest, and occasionally reuses it. Other than that little eccentricity, the European paper wasp acts much the same as our native wasps.

In the spring, watch your high traffic or “collision course” areas like under deck railings, inside gas grills, and behind basketball goals for nest-building activities. If you catch them early enough, typically when the queen is still the only adult, you can remove the nest while she’s away. She’ll most likely look for a safer spot elsewhere.

There are times when an established nest just has to go. Paper wasps especially tend to nest in high traffic areas such as under pavilion roofs or garage eaves, although hornet nests have appeared in brush beside garden paths and under porches. When that happens, no one will blame you for removing the offending nest. See “Eviction Notice” on Page 57 for tips on safe nest removal.

An interesting tradition in the Old South recommends painting porch ceilings and window frames with a particular shade of light blue, called “haint blue,” to discourage nest building. Supposedly, haint blue so closely resembles the sky that it confuses wasps, and they look elsewhere for nest sites. More likely, haint blue was originally a “milk paint” or “lime paint” with high alkalinity to irritate wasps. Still, haint blue is a pretty color for porch ceilings, and it can’t hurt to try it.

All successful battle plans need to consider all angles and possibilities, including those against garden pests. Paper wasps and hornets represent a powerful weapon in your pest-fighting arsenal – fighter jets if you will – seeking and destroying pest caterpillars before they can lay waste to your garden. Respect their airspace and they will return the favor, while becoming unexpected allies in the garden.  

Eviction Notice

It happens occasionally: Midsummer you stumble across a wasp or hornet nest in an incredibly lousy location. It’s huge, and in a location you need to frequent, preferably without getting stung. What do you do?

First, get a feel for the area during the daylight. Pay attention to angles of approach (you will need to get fairly close to the nest), as well as escape routes (you may need to beat a hasty retreat). The good news is that while wasps and hornets are active during the day, you’ll be removing the nest after dark.

Second, purchase two cans of an aerosol wasp and hornet killer, preferably one that uses pyrethrin as an active ingredient. Pyrethrin and its chemical derivatives, pyrethroids, are relatively low impact pesticides with a short degradation period, meaning they break down quickly. Most wasp killers have an effective range of up to 20 feet. You should only need one can; the second one is for backup.

After dark on a cool, moonless night, arm yourself with the aerosol spray, safety glasses, and a red-bulb flashlight or flashlight with a red filter. Wasps and hornets do not see red light as well. Approach the nest as close as you feel comfortable, and soak it down with the aerosol can. Be sure to position yourself where you will not be showered by pesticide.

Hornet and yellow jacket nests require more bravery, as you need to get right up in front of the nest and shoot the pesticide in through the entrance. You can’t simply soak down the outer shell.

After spraying the nest, take a shower and launder your clothes to get rid of any pesticide drift. Wait 24 hours before inspecting the nest for any activity, and remove it if there is none. After removal, scrub the area down with soap and water to remove scent markers. Do this only if you can safely access the nest. Some people prefer to bag the nest in a heavy duty garbage bag when they spray it.

Andrew Weidman lives and writes in Lebanon Pennsylvania. He has been watching and investigating insects ever since he was a child, and yes, he still has his childhood insect collection.