Predator Profile ~ Grass Carrying Wasps, Isodontia spp.

Grass-Carrying Wasps ~ Isodontia spp. 

There are a number of ways to attract beneficial insects to your landscape. Planting a diversity of native plants is an easy, win-win solution. Not only do the plants attract many types of beneficial insects including solitary wasps, but they help support a functioning, complex ecosystem.

One of the most interesting solitary wasps in my landscape is the grass carrying wasp. Several years ago I purchased a bell-shaped wire frame. I filled the openings with hollow stems from native perennials in my yard to see what types of solitary bees would use the cavities. I was surprised to find that the primary insect that uses these cavities is the grass carrying wasp, a welcome resident.

Grass-carrying wasps are predators of crickets and katydids. Females sting their prey in the head or thorax which causes paralysis. The immobile prey is carried back to the nest located in cavities in hollow stems, holes bored in wood or openings in rocks. Prey, alive but immobile is stocked in the nest. When enough prey is cached the female wasp lays an egg in the cavity near the prey. Prey becomes food for the developing wasp larvae to feed upon. Females collect grass pieces carrying strands clasped in their mandibles. In my landscape, I have observed them picking up pieces of little bluestem, Schizachyrium scoparium grass blades.

Little bluestem on my 'prairie' slope.
Grass-carrying wasps use the grass blades in their nests.

They use these pieces of grass to divide their nesting cavity into sections as well as close the cavity. Look for pieces of grass stuffed into the ends of the board holes.

Grass carrying wasps are medium-sized thread-waisted wasps with a black head, thorax and abdomen. Their wings are medium to light brown. Similar to the majority of solitary wasps they are very docile and not aggressive towards humans - even near their nest.

These wasps visit a number of native perennials to feed on nectar. They perennials include common boneset, Eupatorium perfoliatum, pale Indian plantain, Arnoglossum atriplicifolium, rattlesnake master, Eryngium yuccifolium, stiff goldenrod, Solidago rigida and mountain mint, Pycnanthemum virginianum.

Remember to leave plant stems and grass blades standing throughout the winter and into late spring. Insects are using the stems as overwintering sites and inside the cavities could be pupae of solitary bees and beneficial insects. Carefully cut the stems in large pieces and lay them on the ground to allow insects to emerge. Grass blades left on the ground once cut will be used by birds as nesting materials or by these grass carrying wasps.

Grass-carrying Wasps ~ Isodontia spp.

Grass-carrying Wasps ~ Isodontia spp. 

Grass-carrying wasps are a flower-visiting solitary wasp, common in late summer and early fall. Because they are solitary-nesting, and not colonial like yellowjackets or hornets, they do not sting humans to defend their nests. It's an important distinction to make with wasps in our landscapes, so many are solitary and not aggressive.

They perform important ecosystem services, pollinating the plants in our landscape, and preying on foliage eating insects, crickets and katydids in particular.

Females look for prey, stinging them several times to paralyze and immobilize them. They carry their prey back to their nests, which are preexisting cavities such as hollow stems or holes bored in wood.

The paralyzed prey are stocked for their developing larvae to feed upon. Using nearby grasses, nests are divided into sections with pieces of grass, they also close the end of nest with grass.

If you erect a mason bee nest board (board with nesting holes drilled in it), grass-carrying wasps will sometimes build nests in the cavities. Look for pieces of grass sticking out the ends of the board holes or plant stems.

I have several different variations of stem nests hung in the yard for solitary bees (and wasps), this one in particular has been utilized almost exclusively by grass-carrying wasps. Cup plant and pale Indian plantain stems work extremely well, both are hollow.

Here's a cross-section of one of those stems with the wasp larvae and stocked prey. In my yard, the grass-carrying wasps like to use little bluestem to seal off the cavities.

Look for grass-carrying wasps in late summer. In my yard, they like to visit stiff goldenrod, common boneset and pale Indian plantain flowers for nectar.