Why you should plant a garden that’s wasp-friendly

Attention, spheksophobes: Wasps just want to help.

And Heather Holm wants to help them make their case to gardeners and others.

Holm, a biologist and pollinator conservationist, knows it’s not an easy sell. But in her recent book, “Wasps: Their Biology, Diversity, and Role as Beneficial Insects and Pollinators of Native Plants,” she asks that we consider wasps — and not just their cousins, the bees — in the plant choices we make and the pollinator-friendly gardens we create.

“If we took wasps out of the equation,” she said, “many of the leaf- and seed-eating insects they prey on would just go unchecked.”

Troubled by cabbage loopers chewing on your brassicas? There’s a wasp for that.

If tomato hornworms try to defoliate your plants, there’s a wasp for that, too — more than one, in fact. There are also wasps that target tarnished plant bugs (a pest with a taste for a wide range of vegetables and small fruits) and ones that prey on brown marmorated stink bugs and fall webworms. All such sustenance is brought back by adult female wasps to provision their nests, as food for their larvae.

One wasp species is even providing scientists with biosurveillance support in the fight against the emerald ash borer, a devastating invasive beetle whose wood-boring larvae are infesting and killing large numbers of native ash trees (Fraxinus) throughout the United States. In areas not yet infested by the ash borer, researchers monitor the prey brought back to nests of smoky-winged beetle bandit wasps (Cerceris fumipennis), looking for remains of the borers, which helps them track the pest’s widening dispersal.

The list of the organic pest control services offered by wasps goes on, and yet it is the wasps that we humans reflexively regard as pests. That reputation is the result of just 1.5% of the total wasp species in North America — the ones that build social nests above or below ground, forming colonies and cooperatively living in multigenerational nests during breeding season to rear the next generation.

The irony: It is the social wasps toward whom we feel anti-social. They have inadvertently tainted our view of the other 98.5% (although, to be fair, the social ones provide ecosystem services, too).

The trigger is typically a run-in (or more likely a run-over, while mowing) with ground-nesting yellowjackets (Vespula). Or a too-close encounter with a nest of paper wasps (Polistes) or perhaps with a larger, more complex nest of bald-faced hornets (Dolichovespula maculata), its many layers of combs enclosed in an envelope. The result is a sting — always delivered by a female — that we just cannot forget.

If the wasps had been nectaring on flowers like sumac or goldenrod, their most-visited woody and herbaceous plant choices, they would have paid us no mind, Holm is quick to point out. But when we threaten their nests — the home to the next generation — their best defence is a good, and painful, offence.

“The flower garden is the restaurant, not their home — they don’t defend it,” Holm said. “But social wasps are very inclined to defend their home.”

FLOWERS A WASP COULD LOVE

Wasps need habitats similar to those preferred by bees — the subject of Holm’s previous book, “Bees: An Identification and Native Plant Forage Guide.” But bees eat a plant-based diet. Their prey-seeking cousins, the wasps, need something more: to be around the specific plants that attract the insects they hunt to feed their young.

No one book could tackle the almost 13,000 species of wasps in North America north of Mexico. In “Wasps,” Holm focuses on the flower-visiting species, social and solitary, the aculeate wasps (some of whom, the Apoid wasps, are the evolutionary ancestors of bees).

Their unfortunate common name? Stinging wasps.

“People have long known these wasps have flower associations,” Holm said. So it mystified her when she scanned the literature about eastern North America that very little had been documented. “It was hard to find even three sentences in old books or research papers that even hinted at their visiting flowers.”

Wasps make up 15% of the total number of flower-visiting insects worldwide. But they are regarded as incidental or secondary pollinators, not the pollination machines that bees are designed to be, with their hairy bodies that pollen granules cling to.

Another anatomical difference: The range of flowers that adult wasps can drink nectar from is limited because their tongues are typically shorter than those of bees. While choosing native plants is important when you’re creating a habitat that supports beneficial insects, the wasps have an additional request: simple, shallow flowers, please.

Plant families with such flower forms include carrot relatives such as rattlesnake master (Eryngium yuccifolium) and golden Alexanders (Zizia aurea). Asters and their kin, including goldenrod (Solidago), fleabane (Erigeron), tickseed (Coreopsis) and boneset (Eupatorium perfoliatum), are also especially attractive to wasps.

So are mint family members, including various mountain mints (Pycnanthemum), horsemint (Monarda punctata) and bergamot (Monarda fistulosa), and likewise milkweeds (Asclepias) and their relative dogbane or Indian hemp (Apocynum cannabinum).

Oh, and lots of wasps love the colour white, as many of those examples underscore.

“If you have white and purple prairie clover side by side,” Holm said, “you’ll likely observe wasps preferentially visiting the white flowers.”

Remember the restaurant-versus-home analogy, she said, and go ahead: Start planting with wasps in mind. Enhancing the garden with their preferred flowers won’t increase your chances of being stung — and it might make your vegetable garden a more resilient place.

LIMITING THE RISK OF GETTING STUNG

No amount of explaining wasps’ role in the order of things or the ecological services they provide will make anyone want the nest of a social wasp along a walkway, under the porch eaves or in any high-traffic area.

But what’s the best way to discourage them from stinging — and to avert the near-inevitable human impulse to spray some chemical from a distance to eradicate an established nest, killing all of the individuals in it?

Intervene early, Holm advised, to dissuade nest-building in high-risk spots, sparing risk to yourself and to whole colonies, above or underground. “Don’t even think of trying to intervene in August,” she said.

One insight toward that end: Yellowjacket females, probably the wasp most often responsible for stinging humans, search out preexisting cavities, like rodent holes in the ground, when they are emerging from winter hibernation in early spring. Try closing up those holes proactively.

And if you had a ground-nesting colony in the yard last year, look there first, Holm recommended, because wasps will often search for and initiate a nest near the site of their natal one.

Similarly, check eaves, overhangs and birdhouses early and regularly for any sign of the construction of a nest comb, she said, “when maybe there is only an occupant or two involved.”

NEST-BUILDING HEROICS AND OTHER TALES

Holm’s strategy for changing our minds about wasps: to keep telling their stories.

Like the one about the great golden digger wasp (Sphex ichneumoneus), whose female may dig only one nest in her lifetime. Still, she puts her all into creating that multicellular burrow in the ground. Using the same vibratory mechanism that bees use in sonication — the buzz pollination of flowers — the female of this thread-waisted species gets to work in a sunny spot with sparse or no vegetation.

“They grab hold of clumps of soil or aggregate with their mandibles,” Holm said, “and vibrate their thoracic muscles, making a sound like the dentist’s drill or like a little jackhammer.”

Or the black-and-ivory-colored Eastern cicada killer (Sphecius speciosus), one of the largest solitary wasps in eastern North America: Each burrow in her nest must be as much as twice her body width — large enough to accommodate the various species of annual cicadas (not the periodical types) that she stashes inside to sustain her young. As if all that excavating weren’t enough, there is also the matter of transporting a parcel that may be twice her body weight, with occasional stops on the ground to rest along the way.

Then there are the species that perform elaborate mating dances and those that stay clasped to their mates to prevent the female from mating with other males.

“Just telling one fun or fascinating story about a wasp people have never heard, with this amazing life history, and what a struggle it is for them to produce the next generation,” Holm said, “that might build a little empathy for those species who are just trying to eke out a living in these ecosystems that we have changed, and not always for the better.”

The next step on her bucket list, after persuading gardeners to add key wasp-friendly flowering plants to enhance their pollinator plantings beyond the bees’ top choices?

She’ll know she has finally succeeded, she said, when she sees evidence on social media that people have moved in close enough to photograph wasps nectaring on the blooms — not just more butterfly photos.

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