They are in low C and D potencies, thereby acting at the physical level for their common indication, to reduce the frequency and severity of insect bites.

Has it been studied?
In the 60s a homeopath by the name of HR. Trexler studied Staphysagria for its effectiveness at preventing mosquito bites. In a study of 421 subjects over a 4 year period, he found this remedy to be 90% effective.