The horse guard wasp, Stictia carolina, is a type of sand wasp from the eastern United States which preys primarily upon horse flies. It is a large, colorful, fast-flying wasp, one of 28 species in the genus Stictia (which occur throughout North and South America), all of which have similar biology. A female wasp of this species may take anywhere from 30 to 60 flies as food to provision each one of her nests; she makes a new nest for every egg she lays. Nests are simple burrows some 15 cm deep, with a single enlarged chamber at the bottom. An egg is laid in the empty chamber, and the female wasp brings back paralyzed flies until the chamber is full, at which point she closes the nest and begins another. It is common for numerous females to excavate nests within a small area where the soil is suitable, creating large and sometimes very dense nesting aggregations.
It is noteworthy that horses and cattle are not disturbed by the presence of these wasps, despite their rapid flight and loud buzzing, even though the same animals can be very skittish in the presence of horse flies or bot flies. Nonetheless, these beneficial wasps are intimidating to many horse owners, who, if not familiar with them, may take measures to eliminate the wasps, thus exacerbating their problems with horse flies.