Horse guard wasp

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 and sometimes silver-spotted skipper larvae until the chamber is full (mass provisioning), at which point she closes the nest and begins another.[2] Numerous females often excavate nests within a small area where the soil is suitable, creating large and sometimes very dense nesting aggregations. Nearly all the prey are biting female horse-flies; exceptionally, other flies such as Odontomyia and the screw-worm fly Cochliomyia are taken.[3]

Horses and cattle are not disturbed by the presence of the horse guard wasp, despite its rapid flight and loud buzzing; the same animals may however respond strongly to horse-flies or bot flies.[1] Nonetheless, these beneficial wasps are sometimes eliminated by horse owners unfamiliar with them, thus exacerbating their problems with horse-flies.

The horse guard wasp acts as a natural biological control, helping to keep horse fly populations down. This makes it important to the economies of those areas where horses are reared; in the words of Bohart and Menke, it "fully lives up to its name".[1]

The generic name "Stictia" may be related to Ancient Greek "stictis" which means "spotted"; the specific name "carolina" is a reference to the eastern American state to which this species is native. It occurs from the 100th meridian eastwards, and as far north as Pennsylvania.[1]