I had a different take on the film than what was covered in the article or in the alternate links. Let me know if this makes sense to anyone else.

(/s
“The Thief is a drug dealer/con-man who is being manipulated by the worms into spreading their offspring to new hosts. This is subconscious so that he doesn’t panic and try to remove the symbiote. Making a street drug from the chemical that allows recreational telepathic communication might be enough to get by if he just happened on to it by chance while he was pouring coke over meal worms, but good old fashioned greed and a mind-worm that needs to propagate made him step up to kidnapping and brain washing to be able to get more funds/hosts.
The Sampler is a previous victim of the worms who figured out a way to remove the parasite himself, and is trying to help other victims out so that they don’t end up like the Thief, thinking they are in control of their lives/bodies, when in actuality they are not. He records clues on how to find him/connect mentally with him so they can be with the lost pieces of themselves that are now living on the farm. He is the hero of the story, and is tragically killed because Kris thought he was the Thief. He drowns the pigs out of fear that their offspring might be able to reproduce in a non-controlled environment like he has on the farm, and would spread more of the mind-controlling worms that have caused so much suffering already. Ironically, this causes the exact thing he is trying to prevent.
The worms don’t only connect to the pig/human. They connect to every living being that they have been in symbiosis with. Kris hears the current running past the tree, The Sampler listens in to various parts of other peoples lives and records re-creations of the noises, Jeff and Kris seem inexplicably familiar with each other at their first meeting, etc. I think the worms are only one part of the cycle. It is the blue liquid that does the mental connections between plant/worm/human/pig/etc. There could be many more involved in the food chain and if the blue liquid had it’s way I am sure every organism on earth would be connected with it.
Quinoa Records, and the farm there, were supposed to be a safe haven where people dealing with the mental anguish of telepathy could find some sort of peace with people who have experienced the same trauma that they have. E.G. Kidnapping, brainwashing, cancer symptoms, unwanted surgery, loss of children, loss of self, death, and rebirth. More than enough to cause a psychotic break in anyone.”)

I loved the thematic elements that Carruth used with color. (/s “Kris’ skin appearing yellowed/jaundiced when she’s trying to find comfort in Jeff’s embrace, the yellow flower in the pool when she has a mental breakthrough, & painting quinoa farms yellow after other victims have come there to find some peace. They are all mentally part flower, and what could be more comforting than the rays of the sun to provide warmth & nourishment?”)