Diggers

Nobody has ever gotten a clear look at a Digger. What people know about them comes entirely from the evidence they leave behind, and that evidence is always the same: a companion vanishes without a sound, and where they stood, blood rises from the sand.
  Diggers inhabit the shifting dunes of the Dune Sea in northwest Lone Star, lurking beneath the surface in a landscape that already swallows footprints within minutes. They are ambush predators of the purest kind. There is no warning growl, no telltale ripple in the sand, no territorial marking to indicate you have entered their hunting ground. A member of a traveling party simply ceases to exist. The others turn around to find a dark stain spreading across the sand where their friend was walking moments before.
  The speed of the attack is what makes Diggers so feared. They drag a victim below the surface so quickly that there is no time to scream, no time to fight, no chance for nearby companions to intervene. The sand closes over the spot as though nothing happened. Unprepared caravans crossing the Dune Sea sometimes lose members without realizing it until the next headcount, finding themselves one person short with nothing but a fading bloodstain to mark the loss.
  Whether Diggers are animals, insects, or something else entirely remains a matter of speculation among the few survivors who have crossed the Dune Sea more than once. The Nezrengal tribe seems unbothered by them, but the Nezrengal are unbothered by most things that would terrify a sane person.