The doodlebugs

Charismatic prospectors did not consistently succeed at finding oil, but they proved adaptable and devised new methods when their authority waned. When clairvoyance and dreams failed to produce oil or convince investors to part with their money, some prospectors began to employ a variety of oil-finding devices such as divining rods. The divining rod and other devices with a more sophisticated appearance acquired the name of doodlebug, which applied to either the apparatus itself or the person using it…

Like a blind man surveying the terrain with a cane, the most successful doodlebug prospectors also surveyed the landscape, and this activity cultivated within them an instinct for recognizing changes in topography and vegetation that indicated the presence of oil…Successful prospectors cultivated an intuition or knack for finding oil by surveying the environment and the doodlebug device may have facilitated that process.

—Brian Frehner, Finding Oil: The Nature of Petroleum Geology 1859-1920