Bug of the Month May 2017: Grass Carrying Wasps found in Home

Subject: Is this an ichneumon wasp?
Location: Austin, TX
April 30, 2017 8:49 am
What is this bug? Finding them inside the house this spring trying to get out…hanging around the windows…do they sting/bite? Any house structure damage concerns?
Signature: Stephen

Grass Carrying Wasp

Dear Stephen,
Based on BugGuide images, we are pretty confident that this is a Grass Carrying Wasp,
Isodontia mexicana.  According to BugGuide:  “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.  Remarks These wasps commonly make their nest in the narrow track found above outer windows.”  We have many more images in our archives of the nests of Grass Carrying Wasps because they are so frequently found in window tracks.  Solitary wasps are generally not aggressive, and rarely sting humans, though that possibility does exist.  Since they are harmless, and since it appears one individual in the images you attached might be dead from unnatural causes, we are tagging this submission as Unnecessary Carnage.  Because Grass Carrying Wasps are emerging from nests formed in window tracks now that spring has arrived, and because we suspect other homemakers might be experiencing similar sightings, we are tagging this posting as the Bug of the Month for May 2017.

Grass Carrying Wasp

Update:  Grass Carrying Wasps reported from France
Subject: Grass carrying wasp
July 25, 2017 5:29 am
Looking at your excellent site, I think you may have resolved two mysteries for me.
We have noticed recently a number of ‘grass carrying wasps’ around our dining table on the terrace. They have been disappearing into the metal frame taking their blades of grass with them. However, without taking the table apart we have been unable to tack where they are going.
I assumed them to be carrying the grass for nesting material and your site confirms this.
What you may have also answered is the reason why over the past couple of weeks, we have been finding a number small, bright green crickets on the chairs and the terrace around the table. Anything from 1 to about a dozen or so at any one time.
We assumed them to be dead but your item on the  g.c.w. suggest that may not in fact be the case.
If I may ask a question – we live in the south-west of France which is a long way from you folks. Can you confirm if these wasps are the same i.mexicana as you have or another entirely different insect altogether.
Many thanks for creating and maintaining the website. I use it often.
Have a nice day y’all.
PS – If I can get a decent photograph I will send it to you.
Signature: Robin Nichols

Dear Robin,
We sometimes have a hard time with French sightings as there are not many comprehensive insect websites devoted to French species, however, folks in the UK seem to really like their bugs.  According to the Bee Keepers Garden:  ” A new to Britain wasp,
Isodontia mexicana (de Saussure), known as the Grass-carrying wasp, has been discovered at Greenwich Peninsula Ecology Park. …  Researcher David Notton of the Natural History Museum said the wasp is pretty docile and a solitary species, so does not form large nests. ‘It’s quite unlike the better known and aggressive yellow/black social wasps with which people may be familiar.  We don’t know how it got to the UK, and although it’s a non-native invasive species there’s no evidence to suggest it’s a threat to UK fauna.'”  Since the Grass Carrying Wasp has been reported in the UK, it might have also been introduced to France.  According to Encyclopedia of Life:  “Isodontia mexicana, the grass-carrying wasp, is one of the thread-waisted wasps belonging to the family Sphecidae. It is native to North America, found east of the Rockies and through Central America, but has recently been introduced into France, where its population is slowly spreading through Europe.” 

Good morning Daniel,
Many thanks for your reply regarding the grass carrying wasp. I have since looked on the internet for information regarding the existence of the insect in France.
According to a (French) Wikipedia entry the wasp arrived in southern France sometime during the 1960’s, since which time it has spread throughout the Midi region (effectively the southern half of France) and is now present in Italy, Spain and Switzerland.
Helped, it is believed, by the long, countrywide heatwave in 2003, it managed to traverse the Massif Central into more northerly parts of France and is gradually spreading further north – presumably as global temperatures rise. I
As you say, it has now also been found in the UK.
Kind regards

2 thoughts on “Bug of the Month May 2017: Grass Carrying Wasps found in Home”

  1. I live in Vancouver WA and for the first time in my 50 years of experience, I have this wasp making its grass nest inside my hanging pipe wind chimes. Are they supposed to live in my state? Is this an anomaly?
    Thanks 7/2018


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