Grass-carrying Wasp, Vol. 8, No. 7
Isodontia mexicana
Order: Hymenoptera
Family: Spechidae
The windchimes just didn’t sound right. They made more of a dull clanking sound than the pleasant tune we were used to. While investigating, I noticed some long, dry grass stems sticking out the top of one tube. Upon turning the tubes on end, I could see that four of the six tubes were packed with dried grass. Then I noticed several dead crickets laying on the deck, underneath the chimes. These crickets were not black or brown, they were green—tree crickets, the kind whose chirp frequency can be used to estimate the temperature.
Of course, the next thing to do was to grab those straws sticking out of the top of the tube and pull. This produced a long plug of grass, with a hollow area filled with several dead tree crickets (see photo). It was a nest. Had to use a long slender stick to push similar nests out of the other three tubes. Now the chimes sounded much better.
Grass-carrying wasps are close relatives of mud daubers, with biology and behaviors that are similar, yet uniquely different. Mud daubers build their nests of mud; grass-carrying wasps use dried grass or similar fibrous materials. Mud daubers hunt spiders; grass-carrying wasps hunt tree crickets, katydids, and certain grasshoppers. Both wasps use their stings and special venom to paralyze their prey before carrying it back to their nests to fill brood cells. Those tree crickets weren’t dead; they were paralyzed. Each cell is stocked with several prey items and a single egg. The resulting larva feeds on the paralyzed prey within its cell, which contains just enough food for it to grow to maturity and pupation.
These wasps are more common than one might think but often go unnoticed because of their dull color and relatively small size. Mature wasps are about ¾ inches long with dark-colored bodies, brown wings, and a long, slender, “mud dauber waist.” These are not flashy wasps, and it is largely because of their nesting habits that most people encounter them, though even then the source of the nest often goes unrecognized.
Grass-carrying wasps build their nests in any suitably sized hole or elongated cavity, holes between around ¼ and ½ inch in diameter. They will use cavities that are oriented both horizontally and vertically. They rarely use holes in the ground, but have been reported to do so, and will sometimes use holes in the sides of dirt banks. In nature, they nest in hollow plant stems or appropriately sized holes left in trees by wood-boring insects. Around homes they nest in drill holes in wood, vacant carpenter bee galleries, bolt holes in machinery, and similar places.
They will also nest in the tracks and channels around aluminum windows and doors. This is one of the most common places where nests are noticed by homeowners, because the nests can jamb windows and sliding patio doors, causing them to be difficult to open or close. “How did that wad of grass get in there?” This is the only real problem these otherwise innocuous wasps cause. That and changing the tune of one’s wind chimes.
See Bug’s Eye View No. 20 of Volume 6 for a brief article on, the Organ Pipe Mud Dauber.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
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