The grass wasp is more commonly called the grass-carrying wasp, and it earns its name by carrying blades of grass and similar detritus to one place to create a nest. These nests are typically tucked into crevices or protected corners like windowsills or cracks in the foundations of houses, and this brings grass wasps into contact with people.
Grass-carrying wasps form the genus Isodontia, of which there are several species. Both Isodontia mexicana and Isodontia auripes are commonly found in the United States, and they both use preexisting cavities in which to build their nests. They are both thread-waisted wasps, with a bulging abdomen and thorax which are connected with a very thin threadlike segment.
During the early summer months, grass-carrying wasps emerge from their cocoons and mate. Throughout the summer and early fall, the female wasp collects small bits of grass and hay in order to build her nest. After the nest is lined, the female wasp paralyzes crickets by stinging them and then brings them to the nest. After this, the female wasp lays her eggs and when the eggs hatch, the larvae feed on the living, paralyzed insect before spinning cocoons and later emerging as adults. In areas with long summers, two generations of grass-carrying wasps can grow up in a single year.
Grass-carrying wasps are less than an inch long, with shiny black bodies and white hairs sprouting from their thorax. Their wings are translucent with a smokey reddish-brown color. The larvae resemble white grubs. Their cocoons are oval in shape and, unlike butterfly or moth cocoons, they have a papery texture.
The only risk that grass-carrying wasps pose is that they sting. Unlike bees, they can sting repeatedly, but they are usually only threatening to people who are allergic to their venom. They are solitary wasps, and so will not swarm. If you find a grass wasp nest, simply remove the grass and throw it away. If you wish to prevent grass wasps from nesting near your home, block up any crevices that might be attractive for their nests.