Are Grass-Carrying Wasps Dangerous Or Beneficial?

Did you find cocoons in your window frame? Most probably, you encountered the pupae of grass-carrying wasps. But are grass-carrying wasps dangerous or beneficial? Let’s find out.

Have you ever noticed strands of dry grass on the corners of your windows?

While these might look like nests of some random pest, they are the home to one of the most beneficial insects from the wasp family, the grass-carrying wasp

Primarily found in the regions of the northern United States, these wasps offer great assistance to gardeners and farmers.

Wondering how? Read this article to learn all about grass-carrying wasps and how they are beneficial. 

Are Grass-Carrying Wasps Dangerous Or Beneficial? Truth Revealed

What Are They?

Before we dive into the details of this topic, let us first understand what a Grass carrying wasp is. 

They are gentle solitary wasps who prefer to nest aboveground in a preexisting cavity like the tracks of storm windows or hollow plant stems.

Grass-carrying wasps are around 0.7 inches long with a pair of smokey red-tinted wings. Their black bodies are lined with long and thin abdomens. If you look closely, you can find some white hair on their thorax. 

Females build nests using grass blades where they feed and nurture the larvae. These larvae are grub-like and have no legs. You can identify them by the yellow-cream color of their body. 

What Do They Do?

These wasps spend most of their life-cycle pollinating flowers and sucking nectar, except when the female wasps are engaged in building and provisioning nests.

Females carry blades of grass to where they build the nest. Using strands of dry grass blades, they make brood cells. These cells are filled with dead tree crickets for the larvae to feed on. 

Once these larvae reach the final stage of development, they create cocoons and transform into pupae and later emerge as adults during spring.

The nesting season starts early in July, followed by adults visiting flowers by late July throughout September. 

Are Grass-Carrying Wasps Dangerous Or Beneficial? Truth Revealed

Are They Dangerous?

Unlike most thread-waisted wasps, the grass-carrying wasps are not aggressive, and they don’t aggressively defend their nests. 

They don’t sting anyone other than the tree crickets and their other prey. If you find wasp nests in your storm windows, make sure you remove them gently.

Remember, these wasps can sting but are harmless until you try to handle them. 

Are They Beneficial?

Grass-carrying wasps are considered highly beneficial. Farmers and gardeners often make efforts to lure them into nesting in their gardens. Here are the two most helpful features of a grass-carrying wasp:

They are excellent pollinators

Since these wasps spend most of their time collecting nectar from flowers, they carry pollens from one flower to another to facilitate the growth of new plant seeds. 

In many cases, These wasps have a particular affinity toward white flowers and tend to visit them more often than the others. 

Are Grass-Carrying Wasps Dangerous Or Beneficial? Truth Revealed

They eliminate pests

Apart from being great pollinators, these wasps are excellent for pest control. Grass-carrying wasps are highly-skilled predators.

The Females are experts in hunting down tree crickets and other pests. They sting these herbivorous prey to paralyze them.

After that, they store the paralyzed prey in the nest so that the growing larvae can feed on it. 

How to Attract Them to Your Garden

Provide a nesting place

As mentioned above, these wasps don’t build their nest in excavated underground burrows; they prefer to nest aboveground in certain cavities.

They usually prefer natural cavities like hollow plant stems or a hole in a wooden log. 

Therefore you can place some freshly cut hollow stems in your field. Make sure these stems are at least 10-inch length and placed horizontally above ground.

You can bundle a few of these hollow stems together with burlap twine to increase the nesting chances. 

Are Grass-Carrying Wasps Dangerous Or Beneficial? Truth Revealed

Maintain a pesticide-free yard

A yard or garden full of pesticides is a significant obstacle to attracting pollinators.

Under no circumstances will an insect feed on a flower sprayed with insecticides over pesticide-free ones. 

To attract grass-carrying wasps refrain from using insecticides in the garden, particularly on flowering plants. 

A good dump of dry grass strands will also attract these wasps as they depend on these strands to build nests.  

Frequently Asked Questions

Are wasps pests or beneficial insects?

Grass-carrying wasps are highly beneficial insects as they are excellent pollinators. These wasps are less aggressive to humans and great hunters of pests like tree crickets. 
Farmers and gardeners try to lure these wasps into nesting in their fields to increase pollination and eliminate pests. 

Do digger wasps have a queen?

Digger wasps are a common species of the wasp family. But unlike other wasp species, they live in and nest alone. 
These wasps don’t have a queen and can be considered a solitary species. Being a solitary species, they don’t show aggressive behavior towards humans if not disturbed.  

What kind of wasps digs holes in the ground?

Cicada killer wasps, also known are ground digger wasps live in the ground in tiny holes and prey on cicadas for food. 
These wasps are solitary species and are generally not aggressive towards humans. They are amongst the most giant wasps and are primarily black, with yellow stripes on their abdomen attached to translucent orange wings. 

Does killing a wasp attract more wasps?

Killing a wasp is not the best way to get rid of these insects. When you kill a wasp, it releases pheromones that attract other wasps nearby. 
So instead of killing one, calmly trap the wasp under a glass. This is called a wasp trap, preventing the trapped wasp from returning to the nest. 

Wrap Up

Grass-carrying wasps are highly beneficial insects, but unfortunately, many people don’t understand their importance and misunderstand them as highly aggressive pests. 

We sincerely hope that you are able to understand the importance of these creatures after reading about them. Thank you for reading!  

Reader Emails

Many readers have asked us to identify these wasps because they tend to look quite menacing and often fly around carrying grasshoppers and similar insects.

Enjoy some of the questions asked and photographs of this insect from our collection of past emails.

Letter 1 – Baldfaced Hornet and Grass Carrier Wasp

 

late summer bugs: baldfaced hornet and ?wasp? Hi Bugman! I am avoiding work by sorting late summer photos. I found a photo of a Bald Faced Hornet, sipping from a nectar river. Do you want a photo of it in one of its favorite “soups”? Also, a wasp that I can’t ID. I checked your wasp pages and bugguide – it seems to most closely resemble Blk& Yellow mud dauber or Ammophila, but the coloring is wrong. Its not a focused photo (sorry), but the abdomen was definitely striped. Both photos were taken mid-August 2005 near Chicago. Your site has been like a daily vitamin to me these past few months – the new photo additions remind me of summer! Jill Anderson, Chicago Hi Jill, Thank you for the sweet compliment. We know exactly what it is like to avoid work, one of the reasons we started this website. Your Baldfaced Hornet photo is wonderful and we will see if Eric Eaton recognizes your Mystery Wasp. Minutes later, Eric Eaton responded: ” The mystery wasp is one of the Grass-Carrier Wasps in the genus Isodontia, closely related to mud daubers. This one is Isodontia elegans. Until rather recently, this species was thought to occur only west of the 100th meridian. I sent specimens I collected in Cincinnati to an expert, and he confirmed the ID. Isodontia are easily identified because they are the only common thread-waisted wasps that rest with their wings flared out to the sides like this. Most other, related wasps hold the wings flat over their back when at rest. There are at least four other species in the genus that are widespread in the eastern U.S. Eric “

Letter 2 – Tree Cricket, probably from Grass Carrying Wasp Nest

 

Subject: Is this a baby praying mantis? Location: Kingston, New York August 10, 2012 5:01 pm HI- My father found a whole bunch of these bugs nesting in his 2nd story windows. They are in 3 different windows always on the north side. IF they are baby praying Mantis– what should we do with them? Thank you! Signature: Maria Juliano
Tree Cricket found in a Nest
Hi Maria, This is a Tree Cricket, not a young Preying Mantis, and it is an adult.  Neither Tree Crickets nor Preying Mantids make a nest for their young.  We suspect your father discovered the nest of a Grass Carrying Wasp.  A female Grass Carrying Wasp makes a nest of grass, often in the tracks of windows, and she provisions the nest with Tree Crickets or other Orthopterans so her brood of larvae that cannot catch food for themselves will have a fresh food supply.  Many wasps provide for young in this manner, and the sting of these wasps has evolved to deliver just enough venom to paralyze the species that the wasp preys upon.  Paralyzing rather than killing the prey ensures that the prey will remain a fresh food source for the larvae instead of drying out.   See BugGuide for additional information on Grass Carrying Wasps.

Letter 3 – Grass Carrying Wasp Nest

 

Subject: A nest of grasshoppers?? Location: Ontario Canada July 8, 2017 10:30 am We opened up our window on the second storey of our home and found this nest filled with these light green insect resembling a grasshopper. I didn’t think that they made nests so I’m not sure if my assumption is correct or how they would even get there. Any info would be really appreciated. Signature: Thanks for any info.
Grass Carrying Wasp Nest
This is the nest of a Grass Carrying Wasp.  The female Grass Carrying Wasp constructs her nest and provisions it.  According to BugGuide:  “Larvae are fed Gryllidae (particularly tree crickets) or other Orthoptera.” 

Letter 4 – Grass Carrying Wasp with Tree Cricket Prey from France

 

Subject:  Update on Grass Carrying Wasp from France Location:  southwest France August 29, 2017 8:05 AM Hi Daniel, Further to recent contacts, I have, at last, managed to get some half decent shots of the grass carrying wasps nesting in our patio table. They have been pretty active these past few days – maybe the 35+ degree heat has turned them on – but they catch me out every time I have no camera ready. It really is a struggle to film them as they arrive and disappear to their nest(s) in no time at all. However, the attached pics show one with a small cricket or grasshopper of some description and another close-up or the wasp just landing on the table. I hope they are of sufficient quality to be of interest. I am still waiting for the shot of the wasp actually ‘doing what it says on the tin’ and carrying a piece of grass to the nest. I have been close a few times and will get it one day, although I figure nesting may well be approaching the end with the impending onset of autumn. We have also noticed recent activity in the table by what I believe are some form of robber or parasitic wasp. The first one looked VERY like a large horsefly, the subsequent visitors more like a regular small brown wasp. Again, I have not been able to capture them on camera so I can’t ID them any better than that I’m afraid. The interesting thing is that they have been bringing in small crickets and the like, using the same holes as the grass carrying wasps. I don’t know whether they are nesting on their own behalf or feeding the larvae of the GCW’s for the benefit of their own offspring. The two species met on one visit to the nest entrance. The prey was jettisoned and there was an interesting ‘face-off’ with the larger, GCW probably winning on points I would say. One final note on the GCW – it dropped its cricket on the table before landing at the nest hole and it was clearly evident that the prey was not dead, merely anaesthetised, as there were distinct signs of movement in both the legs and the ovipositor. I have no idea how long it is, following the bite, before they die  but this one didn’t seem to last more than a few minutes before it (seemingly) expired. Thanks as ever for all you do to enlighten us on these matters. My wife thinks I spend an “unreasonable” amount of time perusing the site but she’s quite getting into our little wasp friends and alerts me now when one is ‘incoming’. There’s hope yet! All the best, Robin
Grass Carrying Wasp with Prey
Dear Robin, Your diligence has paid off.  We love the image of the Grass Carrying Wasp with its Tree Cricket prey.
Grass Carrying Wasp

Letter 5 – Grass Carrying Wasp Nest provisioned with Crickets

 

Subject:  Wasps? Geographic location of the bug:  Nest uncovered during window replacement Date: 07/10/2019 Time: 09:44 AM EDT Your letter to the bugman:  Have read many accounts that wasps paralyze and lay eggs in these “victims”? How you want your letter signed:  Sue
Grass Carrying Wasp Nest with Crickets
Dear Sue, We wish you had a higher resolution image.  We have never seen an image of such a fully stocked Grass Carrying Wasp nest.  Female Grass Carrying Wasps provision the nest with Crickets, especially Tree Crickets.  We had no idea each larva would eat so many Crickets.  We were under the impression that one cell was used per egg.  We will need to research this matter more.  Your understanding of the behavior of solitary female Wasps and their care for the young is correct.  Paralyzing the prey allows the victim to remain alive and fresh as opposed to old and dried out, so if the eggs hatch in several months, there will be fresh food provided for the long dead mother Wasp.  Social Wasps like Hornets have no need to paralyze prey as there are worker Wasps assigned to child care so the queen can just procreate.  Where are you located? 
Close-Up of Grass Carrying Wasp Nest with Crickets

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

2 thoughts on “Are Grass-Carrying Wasps Dangerous Or Beneficial?”

  1. I use to just have one or two windows, today, I had these little green ugly kadydids in straw in bedroom windows only one side, north windows and even in my kitchen window, dinning room and living room, they are everywhere. I did notice so many crickets this year while gardening. I just get a kitchen knife clean out the window side pane and kill them. How to get rid of them permanently. I hate these critters, they (some) of them turned into magots . ( ugh)

    Reply
  2. This is cool — I just found similar nests with paralyzed katydids – but in the pipes of some wind chimes (I was cleaning them because the chimes didn’t sound right!) I was a little worried about what I might find. I found a few larva and cocoons and didn’t know what they were until I found an old cocoon that I opened and found a fully formed, small, wasp in it! The chimes were packed with grass nearly 4-5 inches worth. I was glad to see “someone” was helping with the katydid population, so I won’t disturb them further. I’m in the East Bay area of Northern California. I guess these wasps are wide-spread!

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