Grassbearer Wasp: A solitary wasp that builds an unusual nest

Grassbearer Wasp: A solitary wasp that builds an unusual nest

Grass-bearing wasps build their distinctive nests in storm window tracks as well as abandoned insect galleries and hollow plant stems.

As interest in pollinator conservation continues to grow, it’s helpful to learn more about the diverse array of native wasps and bees that can be found in our backyards. You may encounter a wasp carrying grass in a bee hotel if you create a wasp that has a variety of tubes of different sizes. In pipes occupied by grass wasps, you will likely find blades of grass sticking out of the pipe.

Bee hotel with grass-carrying wasp nests. Photo by Nate Walton, Michigan State University Extension.

Unlike some other solitary wasps, grass-bearing wasps prefer to lay their eggs in nests made in cavities above the ground. In nature, females of these solitary wasps occupy hollow plant stems or galleries abandoned by other species. In built environments, grass-bearing wasps choose a variety of artificial cavities, as long as the size and shape are appropriate. For example, storm window frame tracks and other cracks and crevices on the exterior of structures are well-suited locations for grass-bearing wasps’ nests.

To build these nests, female wasps carry leaves of grass to their chosen cavity. There, the brood cells are lined with grass and stocked with paralyzed tree crickets for the wasp larvae to feed on. The female wasp searches for tree crickets (subfamily Oecanthinae) in hidden places and uses her stinger to paralyze them before returning them to the nest. The paralytic agent in wasp venom keeps the cockroaches alive and preserves them until the wasp eggs hatch and the larvae begin feeding. Once the larvae are fully developed, they make paper cocoons and pupate where they wait out the winter before emerging as adults the following spring.

Cricket tree on pink flower.
The tree cockroach (subfamily Oecanthinae), the primary prey item chosen by some species of grass-borne wasps to feed its developing young. Photo by Nate Walton, Michigan State University Extension.
Grass wasp cocoons.
Dried grass and cocoons from a grass-bearing wasp nest were found in the window track. Photo by Diane Brown, Michigan State University Extension.

Grass-bearing wasps are native to North America. They belong to the family of thread-waisted wasps (Sphecidae) and are in the genus Equality of teeth. Adults are about 3/4 inch long and shiny black. They do not sting anyone other than their prey and are not aggressive unless you try to handle them. They spend most of their adult lives visiting flowers and sipping nectar, except when females are busy building and providing nests.

Native plants are attracted to include goldenrod (Solidago spp.), master rattlesnake (Eringium eucalyptus), mountain mint (picanthemum spp.) and the bone group (Eupatorium perfoliatum), among others.

For more information about these and other beneficial insects from Michigan State University Extension, visit the Michigan Pollinator and Michigan Gardening Initiative websites.

Wasp carries grass on Goldenrod.
Wasp carrying grass on Goldenrod (Solidago sp.) Photo by Nate Walton, Michigan State University Extension.

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