Desert bats, from the order Chiroptera, descended from species native to Old Terra and remarkably adapted to thrive in the hateful cradle that is Arrakis. My interests lie solely with cielago, Chiroptera modified to carry distrans messages. Distrans technology allows information to be implanted in an animal, to be retrieved later.
These subliminally stored messages can be retrieved by uttering the correct word or phrase. The Fremen, as well as certain assassins on Arrakis, use distrans animals for covert communication. Fremen sietches included nesting holes teeming with bats. Vermin squatting and hiding amidst their own filth in deep caves… the fellowship between Fremen and bat becomes easy to perceive.
One must wonder, with the extermination of the Fremen, how many delicious secrets are fluttering about out there in the nighttime sky?