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University of Minnesota Extension

Species guide - species detail

Isodontia? mexicana? (Grass wasp)



Isodontia are solitary wasps in the family Sphecidae. There are several species of Isodontia in North America, but in the MN Bee Atlas we have recorded only one species so far; Isodontia mexicana. If you receive this taxon name it is because your specimen looks like I. mexicana, but is likely in poor shape or lacks features to definitely identify it as Isodontia mexicana.


Isodontia mexicana are large black wasps, almost an inch long, with long legs and their abdomens are on a thin stalk. They do not fold their wings at rest. Don’t be intimidated by their size; like the bees that use our blocks, these wasps are solitary nesters and are not aggressive..

Nest Structure

Each female builds her own nests. You may see females carrying dead grass to their nest tunnel and re-arranging it. If you are lucky you will see a mother wasp carrying back a tree cricket. Grass-carrying wasps stock their nests with paralyzed tree crickets and katydids as food for their larvae. The nests are a little more flexible then bee nests in that cells are not always well defined and more than one larva may share a cell. The nest plugs are made of the same dried grass, either swirled around in the hole or sticking out a bit. Plugs are generally unmistakable and not easily confused with other types. When mature, the larvae spin a large oblong dark brown cocoon, sometimes with a papery outer layer.

Hole Sizes

Larger holes, Column 1 and bottom of column 2 on Bee Atlas blocks.


Multivoltine. Grass wasps can have 2 generations per year in Minnesota. I noticed this in my own block in 2016. You may see completed grass plugs, which then are entirely removed or appear to have a gap in their center. Then later in the summer you may see new complete grass plugs as the second generation begins to build their nests.

Activity Period

Summer into early fall.


No information at this time.

Minnesota Record Map

These data are from the Minnesota Bee Atlas project.

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