Isodontia
Isodontia mexicana (Grass wasp)
Taxonomy
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.
Description
Isodontia mexicana are large black wasps, up to one inch long, with long legs. Their abdomens are narrowly connected to the thorax and appear to be on a thin stalk. They do not fold their wings at rest. Don’t be intimidated by their size, Isodontia mexicana are solitary wasps and are not aggressive.
A grass plug of a grass wasp in a Bee Atlas block (Photo courtesy of C.Satyshur)
A grass wasp in a hole of a Bee Atlas block (Photo courtesy of C.Satyshur)
Nest Structure
Each female builds her own nests. You may see females carrying dead grass to their nest tunnels and re-arranging it. If you are lucky you will see a mother wasp carrying back prey to provision her nest. Grass 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 larvae 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 you may also see a papery outer layer.
Hole Sizes
Isodontia mexicana nest in the larger holes in Bee Atlas blocks, in column 1 and lower column 2 (5/16-7/16").
Voltinism
Grass wasps are multivoltine, meaning they have multiple generations in one season. Grass wasps can have 2 generations per year in Minnesota. You may see completed grass plugs in early to mid summer which are later removed entirely or appear to have a gap in the center. Later in the summer, you may see new complete grass plugs in the same hole.
Activity Period
Summer into early fall.
References
No information at this time.