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Isodontia mexicana, the grass-carrying wasp, is one of the thread-waisted wasps belonging to the family Sphecidae. It is native to North America, found east of the Rockies and through Central America, but has recently been introduced into France, where its population is slowly spreading through Europe. It also has been introduced into the pacific, where it is found in Oahu, Hawaii and Midway atoll. These are not aggressive wasps, nor do they actively defend their nests. They are named for their habit of bringing grass blades to line their nests, which they build in natural cavities such as old carpenter bee holes, hollow tree branches and around storm window tracks. The nests of grass-carrying wasps are divided into individual cells, one for each egg that they lay. After laying, the female wasp provisions the cell with an incapacitated but live grasshopper, usually a katydid (Tettigoniidae) or tree cricket (Gryllidae), which she stings to paralyze. She then plugs the hole with grass, which can often be seen protruding from the nest, to prevent parasites, especially dipteran (e.g. families Chrysididae, Pompilidae, Crabronidae) and hymenopteran (e.g. Bombyliidae, Phoridae, Sarcophagidae) brood parasites, from laying eggs with her larva and competing with it for the provided food. As the legless, grub-like larva develops, it generally consumes the whole grasshopper, then pupates and emerges as a 20mm long black adult wasp with dark brown wings.

Grass carrying wasps are sometimes seen as a nuisance when they build their nests around houses. Pesticides are generally not needed to rid a home of these insects, disrupting the nest is usually enough.

(Jacobs 2009; O'Neill et al. 2007; Wikipedia 2011)


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