Habitat modifiers are various Fungi, Mould, Flora, or Biofilm growths spread by aliens as a means of Terraforming. Often they convert atmosphere, soil, and water into substances beneficial to the invading species, while making them hostile to indigenous life forms. Often, they also provide invaders with a ready foodstuff. In extremely rare cases, they can infect native organisms and subvert their biology to match the invaders, often adding a mind-controlling parasite or tumor.
Expect someone to touch it, and examine closely the residue on their hand.