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Extension > Yard and Garden News > Ground-nesting solitary wasps

Friday, July 29, 2016

Ground-nesting solitary wasps

Jeff Hahn, Extension Entomologist

There have been a lot of questions about solitary wasps lately. The most common questions have been about cicada killers (Sphecius speciosus) but residents have also seen great golden digger wasps (Sphex ichneumoneus), steel-blue cricket hunters (Chlorion aerarium), and sand wasps (Bembicini).
Cicada killer returning to its nest with a paralyzed cicada. 
Photo: Jeff Hahn, UMN Extension

These wasps are generally large insects. Cicada killers range in size from 1 – 1 ½ inches with a stout body, black and reddish brown thorax, amber colored wings, reddish brown legs, and a black abdomen with yellow bands. Great golden digger wasps are about one inch in length, a more slender body with a black head and thorax covered with short golden hair with a reddish-orange and black abdomen and reddish-orange legs. They have smoky, dark colored wings. Steel-blue cricket hunters are also about one inch in size and relatively slender with iridescent dark blue bodies and wings. Sand wasps are smaller, most are close to ½ inch in length and are typically black and yellow.

Great golden digger wasp with a captured katydid.
Photo: Jeff Hahn, UMN Extension
Their biology is similar to each other. They nest individually in burrows but are gregarious, i.e. there are many nests in a small area. They hunt specific insect prey, paralyze them, and bring them back to their nest to feed to their young. Cicada killers seek out cicadas; great golden digger wasps hunt katydids, steel-blue cricket hunters capture field crickets and sand wasps, depending on the species, look for a variety of different insects, especially flies.

These wasps can be common in lawns, gardens, areas adjacent to sidewalks and driveways, and areas with patio stones. Typically they are found nesting in well drained, light textured or sandy soils. The females are not aggressive and while they are capable of stinging will only do so to defend themselves. Males can aggressively guard a territory and will challenge other males (even people) but they lack a stinger cannot harm us.
Aggregation of dozens of great golden digger wasp nests (with
dozens more to the right).  Photo: Jeff Hahn, UMN Extension

They do not injure turf, nesting in areas where the lawn has thinned or existing bare spots. There can be a large quantity of dirt that is dug up which can be unsightly. It is possible that their tunneling can undermine patio bricks but nothing worse than that. Some people are frightened by them because of their size and perceived threat.

There are a couple of options for dealing with ground nesting solitary wasps. The first is to ignore them. They are not causing any real harm and are not dangerous to people. They will go away eventually on their own sometime during August. However, if they were present this year, they will probably nest in the same area next year.

Sand wasp with paralyzed leaf-footed bug prey.
Photo: Jeff Hahn, UMN Extension
If control is desired, it will be necessary to treat the nests with an insecticide. Generally spraying the nests is not very effective. Instead, apply an insecticide directly into each individual nest entrance. Dusts are most effective; granules and sprays can also help reduce numbers. Effective active ingredients include permethrin and carbaryl. If you rather, you can also contact a lawn service to treat the cicada killers for you.

4 comments:

  1. Really interesting article and cool photos on a timely subject. I'll keep an eye out for these guys when I'm out netting and looking for EAB with the UMN Wasp Watchers project this summer. I've actually found quite a few active sites to monitor already, so I'm a little surprised you didnt mention our friend - and EAB nemesis - Cerceris.

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  2. I have heard that wasps are beneficial since they prey on other bugs generally. Why are people encouraged to exterminate them for superficial reasons (i.e. the look of the patio?) It seems we are well advised to support the wasps and avoid killing them. What is up with the anti-wasp sentiment from Master Gardeners? Thanks!

    Jenny B.

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  3. Can you help me in the next few day before a garden tour for the Garden conservancy by Sept 17th?

    Do you know how to stop the wasps from locating there next in a Japanese dry garden with gravel near a stream and flowers are near by too. if we can encourage them to place there nests in another location it will not be a problem . the problem is the Japanese gravel dry garden is to be a pure sea of gravel not with mounds of dirt at each of there nests where allowed to be placed there. many many keep being made. i have tried to just dig them up and remove them but the still keep coming back even at this time of year. The real major problem the garden is about to be viewed by the public this Sunday. I have contently had to keep digging the nests away. they seem to also be trying to did into lawn areas of moss adjacent to the gravel garden.

    Thank you , Robert Cohen, Westport, CT
    this is the link to the garden tour:
    https://www.gardenconservancy.org/open-days/garden-directory/the-blau-gardens

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