Men who had died in storms of the Great Desert had been known to linger on in Middle-earth as tortured spirits known as Sand Devils. They maintained a semi-material form with the appearance of miniature, sand-choked whirlwinds, and traveled across the open wastes of the desert searching aimlessly for lives which they could end. Their form also made for perfect camouflage in their environment, since ordinary whirlwinds were not at all uncommon in the region.
A Sand Devil attacked by enveloping its prey inside its cloud-like body, clogging the foes eyes, ears, mouth, and nose with a mass of swirling sand. The sand also tore at the victim's flesh.
Sand Devils were susceptible to magical attacks, but they were most vulnerable to water. For this reason, many experienced Haradan travelers journeying across the Mirror of Fire or the Dune Sea carried their water bottles open and ready, figuring that the loss of water was worth the insurance.