A Scavenger is a drone or Skimmer-like entity found at Thargoid Surface Sites. They are presumably Thargoid devices that perform some sort of function related to the Sites. They've been observed to nourish or fertilize the alien eggs on the surface.
Considerably smaller than Unknown Ships, Scavengers are non-hostile until fired upon, and their only apparent weapon is the ability to spray a lightly-damaging corrosive liquid at attackers. They can be easily destroyed using conventional Scarab weaponry and drop various Materials: Unknown Fragments, Unknown Carapaces, Unknown Energy Cells, Unknown Organic Circuitry, Unknown Technology Components, Unknown Ship Signatures, and Unknown Wake Data.