Grass-carrying wasps are common across America, and if you have seen one, you might get intimidated by them. But does a grass carrying wasp sting? We looked it over, and here’s what we found.
These wasps are beneficial in the garden and only sting if provoked or threatened.
They are not threatening or aggressive and usually do not cause humans any trouble.
Except for the nuisance of their nests made from dry grass, which ends up on window frames, there is no reason to want to get rid of them.
Continue reading if you want to learn more about these unique and interesting creatures.
What Is This Bug?
The adult wasps of this species are around 7/10th of an inch long with black bodies and red-brown wings.
Their narrow waist connects their abdomen to the thorax. The thorax is covered with white hair. Their larva is grub-like, cream-colored, and legless.
Grassy carrying wasps are solitary wasps that live above the ground (unlike mud daubers or digger wasps). They usually come out of their cocoons during July and August.
During this time, they visit flowering plants for nectar. Female wasps collect tree crickets and katydids to provide food to their larva.
The females also collect blades of grass to make a nest for their larvae. These nesting sites are made in wood cavities, hollow plant stems, bee nests, and human window frames.
These wasps either create individual brood cells partitioned with blades of grass or build a common nest area where multiple larvae can feed and grow.
There are several species of grass-carrying wasps, but Isodontia Mexicana is the most common in the United States.
Homeowners typically come face to face with the nests of this wasp when they are replacing their window screens with storm windows in preparation for the coming winters.
Does It Sting?
It is pretty unlikely for a grass wasp to sting you since they are usually unbothered by human presence and don’t defend their nests.
However, this black wasp may sting you if it feels threatened or provoked, and their sting does carry a punch, so it is best to keep a safe distance from them and just watch them from afar.
Is It Venomous?
Yes, a grass-carrying wasp is venomous, but the venom is harmless to humans. The wasp uses its venom to prey on tree cricket and smaller insects.
Like many parasitoid wasps, they paralyze their prey and leave them near the larvae in their grassy nest. They do not use their venom upon anyone else except for their prey.
Is It Aggressive?
These wasps are not known to be aggressive. They wouldn’t even defend their nests from breaking, and if you remove the nest, they often won’t rebuild it in the same spot.
The good thing is that grass-carrying wasps are non-social and, thus, do not live in colonies. So, you can quickly get rid of their nests if they annoy or irritate you.
What Should You Do If You Get Stung?
Even though grass wasps do not sting humans, they may break their habit once in a while. So, here are some things that you can do if you get stung.
- Remove the stinger with a tweezer or credit card.
- Apply an ice pack to the affected area for at least 20 minutes
- Wash the area with soap and water and apply hydrocortisone cream to it
- Take an antihistamine, like Benadryl, to get rid of itching or swelling
- In case you are in pain, take acetaminophen (Tylenol) or ibuprofen (Motrin)
- If you haven’t taken a tetanus booster for more than ten years, it is advisable to take one in the next few days
In most cases, a sting from a grass-carrying wasp wouldn’t hurt unless you are allergic to insects.
In that case, it is best to follow the above steps and seek medical help if the symptoms start to get worse.
What Does It Feed On?
When it comes to food, the adults and larvae have different preferences. While the adults like to drink from certain native flowering plants, the larvae need insects to grow and develop.
These insects contain protein which is important for the growth and development of the larva.
Unlike adult grass wasps, larvae feed on tree crickets and insects from the family Gryllidae.
The female wasps collect tree crickets, katydids, caterpillars, and other similar insects from gardens and take them to the ‘nursery’ of their larvae.
The larva will carefully feed on the insect, first sucking out the juices and then feeding on the remaining body parts, leaving the heart and nervous system for the last.
This is to ensure that the larvae always get a fresh meal!
The adult wasps, on the other hand, feed on the nectar from flowers of native plants. Like other wasps, they, too, have a preference for plants with white flowers.
They get energy from their nectar, especially the females, who need it to hunt and take the food to the nests.
While feeding on the nectar, the pollen from these flowers also gets stuck between their legs, and they act as excellent pollinators by depositing the pollen in far-off places.
Are They Harmful Or Beneficial?
These wasps are beneficial insects who visit a variety of flowers to drink nectar and therefore contribute to plant life as pollinators.
Besides, they also hunt and prey on garden insects like tree crickets and others from the Gryllidae family and help keep your garden and parks clean.
Probably the only harm these wasps can bring you is that they can build cocoons in the cavities of wood, including the frames for your storm windows.
Also, if you are allergic to insect bites, their sting may cause problems.
Frequently Asked Questions
What attracts wasps to sting you?
Wasps are usually attracted to flowers or prey. They may sting you mistakenly while you are handling flowers, but it is pretty rare.
In your presence, they may sting you if they feel threatened or their nest seems to be in danger. Thus, it is for the best to avoid being around their nests.
Do wasps make nests in the grass?
Wasps usually build their nests in trees, but some may nest inside burrows that they build in the ground.
The nests of grass-carrying wasps, however, are made in wood cavities, abandoned insect nests, and plant stems.
Do wasps live in the grass?
Wasps usually live in and around grass because many of them hunt garden insects.
Many also feed on flower nectar, honeydews, food, and other sugary substances. Thus, you might often find wasps hovering over lawn grass.
Grass-carrying wasps use blades of dry grass to make nests for their larvae, so these wasps are often found near the grass.
What are the wasps that hover over the lawn?
Blue-winged and grass-carrying wasps are two of the many wasp species that hover over the lawn for food and prey.
Both feed on sugary substances and use paralyzed prey to feed their larvae.
Grass-carrying wasps need grass blades to make their nests. Blue-winged wasps lay their eggs on grubs and therefore are often found hovering near the ground.
So, to answer the question- yes, grass-carrying wasps can sting you if you try to mishandle them.
But otherwise, these little guys are very non-aggressive and don’t come in our path for any reason whatsoever.
They simply lead their lives preparing nests for their young ones and sucking nectar from flowers.
They are not even big on defending their carefully prepared nests. If you find and break their nest, they would simply stop making one in that location since they would see it as a sign that the location is unsafe.
Thank you for reading!
Wasps always have a bad reputation, no matter how beneficial they are to us.
Over the years, readers have often asked us about grass-carrying wasps and how harmful their stingers might be.
Go through some of these mails, which can be quite entertaining at times!
Letter 1 – Grass Carrier Wasp perhaps
grass-carrying wasp? July 10, 2010 I found these black wasps all over the Ampelopsis (porcelainberry) vines that seem to be blooming on my back fence. I figured they were potter wasps, and from looking at bugguide my best guess is a Grass-carrier wasp http://bugguide.net/node/view/223506#313917 and I saw you don’t have many photos of them, perhaps you’d like one more? Sara NJ Hi Sara, We can neither disagree with your identification nor confirm it. We hope that one of our readers is able to confirm that your wasp is indeed a Grass Carrier Wasp. The images on BugGuide do tend to support your presumption.
Letter 2 – Grass Carrying Wasp
Grass Cutting Flying Location: Southern NH August 1, 2011 6:40 pm I was recently enjoying some time in my yard, relaxing under the shade of a maple tree when from the corner of my eye I saw what appeared to be a bit of hay or dried grass floating from the sky. As I watched the floating vegetation I realized that it wasn’t floating at all but headed in a direction, with purpose, into a small hole in the axle of my wheel barrow. Of course with my curiosity peaked I watched and to my surprise a hornet looking/flying ant-ish insect popped back out and within a minute was back again with another bit of grass. This continued for as long as I watched and managed to get a picture. I checked under the hornet/wasp directory but did not see anything resembling my little ’bugger’. As far as I could tell he/she was acting alone going back and forth cutting off dead tops of long grass and bringing them back. It was captivating to watch but now I must know what it is and what it was doing (and whether or not I should be worried that it is starting a grass collection in my wheel barrow (stinger?) . . . Thanks Bunches Signature: Nicole in NH Hi Nicole, We got tremendous pleasure reading about your observations of this Grass Carrying Wasp in the genus Isodontia. According to BugGuide: “Females make nests in a tree, hollow stem or other cavity, divide into sections and close with grass. They provision with Orthoptera (Tettigoniidae, Gryllidae). Can be two generations per year (I. mexicana in PA).” BugGuide also provides this information: “Taken from the Internet Reference below (Penn State): The adult wasps emerge from their cocoons in early summer, mate, and the females locate a suitable nest site. She collects blades of grass and grass and hay stems to line the nest cavity. The wasp can be seen flying through the air with the blades trailing beneath her. She lands at the hole and enters, pulling the blade in behind her. After the nest is prepared, she hunts for tree crickets (i.e., Oecanthus sp.), captures and paralyses them with her sting, and transports them to the nest. She deposits eggs in the nest and the emerging larvae will feed on the living, but immobile crickets. When the larvae reach the appropriate size (in 4–6 days at 70–75° F.), they spin a cocoon and pupate. The adult wasps emerge in 2–3 weeks. In Pennsylvania, Isodontia mexicana typically produce two generations per year.” If that timeline is accurate, you can expect your wheelbarrow to be out of commission for about a month while it is being used as a nursery should you desire the young Grass Carrier Wasps to develop without incident. Well I must say Thank You very much for your quick response and solving this mystery for me. I have another wheelbarrow that I’ll use for now since I have sort have taken a liking to the little critter and the free lawn mowing! 😉 Thanks again!! -Nicole
Letter 3 – Great Black Wasp
Subject: wasp which brings confusion Location: indianapolis indiana August 5, 2012 9:48 am this is the first summer I have seen these. started noticing them pollinating my mint. have done internet research but cannot decide what they are. have asked around 2 friends for their opinion and no 1 can decide either. Signature: harley page Hi Harley, We believe this is a Grass Carrying Wasp, Isodontia apicalis, and it is not considered an aggressive species. The individual in your photograph appears to be dead, perhaps the result of Unnecessary Carnage. We based our identification on this BugGuide image which has a comment from Eric Eaton with this description: “The silver face and pale pubescence on the thorax is pretty distinctive. … Differences are so subtle among the sphecids in general that it just takes years of practice to differentiate.” Sadly, your photo does not show the face. We will try to contact Eric Eaton to see if we can get a confirmation or a correction to that identification. BugGuide contains some fascinating information on the genus, including: “Females make nests in a tree, hollow stem or other cavity, divide into sections and close with grass. They provision with Orthoptera (Tettigoniidae, Gryllidae)” and “These wasps commonly make their nest in the narrow track found above outer windows.” Correction Courtesy of Eric Eaton Daniel: Pretty certain that is actually a Great Black Wasp, Sphex pensylvanicus, one that hunts katydids and digs an underground burrow. It does look like a female, so it should have been very large (inch-and-a-half or so). Eric
Letter 4 – Grass Carrying Wasp
Subject: Grass Carrying Wasp Location: Southampton, NY July 18, 2013 4:23 am I apologize for not doing my due diligence when first submitting my photo a week or so ago. I should have searched the web sooner using obvious key words. The photo I submitted is clearly a Grass Carrying Wasp as the image shows it’s carrying grass! Pretty amazing. I’m glad to hear they’re not aggressive. Many thanks for what you & your team are doing. I really enjoy looking through the posts. Sincerely, Lorelei PS You need not respond as I know you are busy. Thanks again! Signature: Lorelei Hi Lorelei, We are sorry we could not respond to your original request because we get considerably more identification requests during the summer than we do during the winter. We are very happy you resubmitted your image once you found an identification for your Grass Carrying Wasp in the genus Isodontia because there is only a single (not very detailed) image of a Grass Carrying Wasp in action on our site, though we do have a few photos of the nests of Grass Carrying Wasps provisioned with Tree Crickets. The Penn State Entomology website provides this information: “The adult wasps emerge from their cocoons in early summer, mate, and the females locate a suitable nest site. She collects blades of grass and grass and hay stems to line the nest cavity. The wasp can be seen flying through the air with the blades trailing beneath her. She lands at the hole and enters, pulling the blade in behind her. After the nest is prepared, she hunts for tree crickets (i.e., Oecanthus sp.), captures and paralyses them with her sting, and transports them to the nest. She deposits eggs in the nest and the emerging larvae will feed on the living, but immobile crickets. When the larvae reach the appropriate size (in 4–6 days at 70–75° F.), they spin a cocoon and pupate. The adult wasps emerge in 2–3 weeks. In Pennsylvania, Isodontia mexicana typically produce two generations per year.” Thank you for providing our site with this gap in our documentation.
Letter 5 – Grass Carrying Wasp from France
Subject: Grass Carrying Wasp from France Location: southwest France August 1, 2017 Hi Daniel, Continuing the theme of the grass carrying wasps, there are 3 or 4 of them nesting in the hollow section frame of our aluminium table on the terrace here in south-west France. They are quite active at the moment and I promised you a photograph if I could get one. Herewith attached. Sadly, I have missed two great opportunities to photograph them – once bringing in a long piece of grass for the nest and the other a day or two ago flying in with a young cricket under its ‘fuselage’. Would have been great shots bout just couldn’t get the camera to hand in time. The do seem to be still nesting and feeding so I will do my best to capture this for you sometime and let you have the images. Whilst writing, I have also attached an image of a spider’s web the like of which I have never seen before. It is fully round in shape (I.e. globe / ball shaped) and abot 2 ½” – 3” diameter, with what I presume to be the owner sitting quietly in the centre awaiting the arrival of its latest prey. It is on the outside of a window, placed in the angle of the frame and the stone wall. Any ideas on what sort of arachnid this may be? Kind regards, Robin Dear Robin, Because your original submission did not include an image, we posted it as an update to our Bug of the Month for May 2017 posting on Grass Carrying Wasps, but the addition of this image warrants its own unique posting.