Spider Holes were typically only used by Japan during WWII, but they were sometimes used by the Americans. Spider Holes originated from the American Civil War and had since evolved into well hidden foxholes.
They had varied success, but were still used throughout the latter years of WWII. Japanese Spider Holes were never really used for observation, but instead for suicide attacks. Soldiers would wait for the main Allied force to pass and then attack the Allied units in the rear.
Some Japanese would even blow themselves up if a tank passed over their hole. Among the places where spider holes were used includes Iwo Jima and the Philippines. Later in the Vietnam War, Spider Holes were used by the Vietcong and US forces alike.