Common name: Grass-carrying wasps
Nest type: dried grass blades
Size: 18-20 mm
Nest tunnels used: 1/2” to 5/16” tunnels
Looks like: Large rusty orange or shiny black waspsIf you’ve ever opened a window and found the tracks bizarrely filled with dead grass and bugs, it’s not the result of a strangely precise wind: you’ve happened upon the nest of an Isodontia wasp, commonly known as the grass-carrying wasps. It might be a shock to see your windows infested with insects (especially wasps!) but if you find them, don’t be alarmed. These wasps are rather un-wasplike, males completely lack a stinger and females only sting if you threaten them. Isodontia females separate their cells and plug nests with grass. They provision their cells with paralyzed, but living tree crickets or immature katydids. The wasp larvae are carnivores, while the adults feed on nectar. The calendar may say October, but it has been warm enough, so you have a few more chances to go bug spotting. Isodontia are active fro mid to late summer, so you still have a chance to see them! If your windows are wasp-free, look in hollowed out tree branches, other naturally formed cavities, or your bee block. We have two species here in Colorado: I. elegans, a lovely rusty orange color, and I. mexicana, a shiny black species. Both have remarkably narrow “waist”, even for a wasp. DID YOU KNOW: Isodontia can produce two generations per year in Colorado. The offspring from the first generation will reuse or use nesting tunnels near their natal nests. You may have only one or two nests in July, but these can quickly multiply to five or ten nests by the first freeze. Isn’t nature great!