What to Do About Sand Wasps?

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The thick waist of this sand wasp shows it is one of the Bembix species.

Everyone recognizes social wasps (yellow jackets and hornets), the ones that live in colonies underground or in paper nest and come to disturb us when we eat outdoors. Sand wasps, though, part of a large group of widely distributed wasps known as digger wasps, are not as well known. And for good reason!

First of all, sand wasps aren’t the slightest bit interested in human activities and certainly not our picnic sandwiches. They are predators, always on the lookout for live insects to bring to their larvae, not human food. So they can be hunting all around you and you won’t notice them.

Plus, although different species of sand wasp are found pretty much all over the world, they tend to inhabit specific habitats that don’t always correlate with human activities. They are especially fond of exposed sites with sandy soil. If that doesn’t describe your gardening conditions, you’ll probably never notice them and you won’t have to read any further. But if your soil is sandy and if vegetation tends to be sparse, you may one day find yourself in a conflictual situation. Wasp or human? Somebody is going to have to give in!

What Do They Look Like?

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This Bembix sand wasp has pale green eyes.

There are many species of sand wasps in different genera, although the genus Bembix, a group of thick-waisted wasps with typical wasplike markings (black with white or yellow stripes, sometimes even pale blue ones), are the most common. They have big eyes, almost like those of a fly, sometimes black, but often pale in color. Another group entirely are the Ammophila wasps, with very narrow waists, usually in shades of brown or black with no striping.

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Ammophila sand wasps, with their narrow waist, look quite different. This one has captured a caterpillar.

The habits of sand wasps are also different to those of social wasps. Rather than buzzing about erratically and fairly hesitantly like yellow jackets, they tend to zoom fairly rapidly to their nest site. Unlike social wasps, renowned for their agressiveness, sand wasps rarely sting and will usually only do so if you threaten their nest.

Their ability to dig is phenomenal: a sand wasp can dig its way into the ground and out of sight in seconds, at least when the soil is workable.

Essentially Beneficial Insects

It is important to emphasize that sand wasps are essentially on the “beneficial” side of the insect usefulness scale. They catch many enemies of our plants and gardens – flies, caterpillars, stink bugs, etc. – and bring them to their nest. Plus they snatch insects that annoy humans directly from the air: house flies, horse flies, etc. What’s not to love about that?

Again, these are not social wasps. Each fertile female digs her own nest, a tunnel with a single chamber at the end. That’s where she lays her eggs (up to twenty) and brings food for her young. The hungry larvae can consume up to 20 insects each over a several week period, so you imagine the sand wasp has be an effective predator: it has a whole hungry brood to feed!

Human/Insect Conflict

I suspect that more than 90% of the time, sand wasps go about their business sight unseen and without bothering people in the least. But sometimes are situations of “disputed territory”.

That’s when sand wasps move into a spot that we humans have set our sights on: a lawn, a beach, a public park, a vegetable garden, a sandbox, etc. They prefer dry areas with little vegetation… which could be description of a too closely cropped lawn.

Moreover, even though sand wasps are not considered social insects and don’t live in colonies, they do like the same conditions. So when one wasp sets up shop in a promising spot, it is usually quickly followed by others and soon the sector is covered in holes with wasps zooming in and out pretty much constantly. Each nest is an individual one, but the “grouping” can be several square feet across.

There can be pet/insect problems too if your cat or dog keeps wandering into the wasps’ territory… although most learn pretty quickly to stay away.

Live and Let Live

Where possible, the best thing to do is simply to leave the wasps alone. They are, after all beneficial, and they rarely take up much space in a given season. If the spot is likely to frequented by people, mark off the sector with orange barricade tape, perhaps adding a sign to explain what is going on. And take the opportunity to explain to your neighbors, friends and children that these insects have a beneficial role to play and should not killed without a good reason.

But sometimes that just isn’t possible. There are lots of situations – playgrounds, public parks, vegetable gardens, lawns that need mowing, etc. – where you simply can’t allow them to live out their lives.

Quick Fix

One short term solution to consider is covering the area with a tarp held flat by rocks or stones. They’ll then be forced to move elsewhere. Or sprinkle diatomaceous earth over the area and into the holes.

Apply either technique at night while they are sleeping to avoid getting stung.

Long-Term Solutions

The following techniques are not adapted to treating current problems, but rather can be useful in avoiding them in future years.

Consider installing dense plantations in their favorite location. Sand wasps prefer exposed soil and are put off by the presence of vegetation.

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Sand wasps, as their name suggests, prefer to nest in sandy locations.

Also, since they usually require sandy soil, you could cover the ground with 6 inches (15 cm) of topsoil and garden in that. Don’t mix the new soil with the sand below, as that will just encourge them to come back. Keep the top layer separate. You have to “bury” the sand for this method to work.

Finally, using mulch can help a lot. It will not eliminate the current year’s problem, as these wasps will not abandon their nest readily and may well find a way through the mulch. But they usually avoid mulched areas when it comes to choosing a location for a new nest.

There you go: a few possible solutions. Just choose the method that suits you best. But hopefully you can reach a truce with these useful and fascinating insects.

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