The Carlisle Mosquito Online

Friday, September 29, 2006


The female wasp prepares her nest. (Photo courtesy of Tom Murray)

Grass-carrier wasp, or the wasp that clogs storm-window tracks

For the past several years, when I try to remove my triple-track storm windows for a rare washing, I find the tracks clogged with packed grass nests. Sometimes these wads of grass have nearly colorless crickets in them and some kind of cocoon. I have also found wasp bodies trapped between the windows, and now I have finally linked these all together.

The culprit of this nest-building is a Grass-carrier Wasp of the genus Isodontia, probably species philadelphica (there are a number of Isodontia species in the eastern U.S.). This wasp gathers pieces of grass often longer than its one-inch body and tucks these pieces firmly into some crevice — into grooves of bark, old hives and commonly into window tracks.

The wasp carries grass clippings to a chosen crack or cavity. (Photo by Susan Emmons)
Like all wasps, these Grass-carriers undergo complete metamorphosis, with egg, larva, pupa and adult stages. Adult wasps emerge from their cocoons in early summer, mate and then the female wasp carries grass clippings to a chosen crack or cavity. She adds to the nest some green tree crickets which she has paralyzed with her sting and leaves them mixed in with the grass as food for the larvae which will hatch from the eggs she lays nearby. When the larvae are about four to six days old they spin papery cocoons and pupate. The adult wasps emerge in two to three weeks.

A solitary wasp

The Grass-carrier Wasps are "solitary wasps" and do not have workers to help build nests and raise larvae. They are usually not aggressive in protecting their nests and sting only when harassed or handled.

The Grass-carrier Wasp belongs to the family of digger wasps, the Sphecidae. These are known as thread-waisted, have shiny black bodies and smoky wings. Unlike the spectacular ichneumon wasps written about recently in this column [Mosquito, August 4, 2006], these wasps are small, ant-like creatures. The cocoons are elongated and a yellow-cream color. Inside, the larvae are grub-like with no legs.

A minor nuisance

She adds some tasty green tree crickets as food for her larvae. (Photo by Susan Emmons)
These Grass-carrier Wasps can be a minor nuisance, but there is no need to spray the nests. The nests can safely be removed with a pencil or flat screwdriver so you can use the window tracks for your windows. No matter what you do — unless you fill the cracks — a new set of wasps will be back next year to take advantage of their favorite site: the window tracks. I enjoyed finding out about this industrious wasp, and it is always good to know who is sharing our homes.

As I have read up on this wasp I find that many people have enjoyed watching wasps as they carry out their wide variety of interesting behaviors — building spectacular nests, killing large insects and carrying them around and observing how through the years they can move from building nests in hollow twigs to using our window tracks. Howard Ensign Evans, a former head of Harvard's Museum of Comparative Zoology (MCZ), wrote a delightful book on his observations, The Wasp Farm.

Another local expert on birds and insects, videographer Dick Walton, has recorded wasps, and you can watch some of these fascinating creatures in action online at

References: The Wasp Farm by Howard Ensign Evans,;;

2006 The Carlisle Mosquito