Humans settle on a planet and use alien beasts instead of machinery. The beasts are in fact sentient and a contract is negotiated to allow the humans to use the aliens. I vaguely remember that there was some conflict around this, as there was an alien faction that refused entering the contract.

Part of the adaptation that the aliens need to undergo involved "sewing" a sap/feed bag onto them (this left quite an impression on my young mind, so I am quite sure of this plot point). Another vivid impression is that the "contracted" aliens that served as vehicles could be put into "idle" mode with an ignition key, similar to an automobile.

I probably read the story in the late 70's, but it had a 50's vibe to it -- can't really define it, possibly a cold-war human-chauvinistic feel). It was kind of a Blish ("Surface Tension") or Campbell ("Who Goes There") style, if that makes sense.

  • Are the aliens just used as vehicles, or are there other uses they are put to?
    – DavidW
    Commented May 26, 2022 at 17:22
  • Don't remember, sorry.
    – user108131
    Commented May 26, 2022 at 17:28

1 Answer 1


This is "The Last Castle" by Jack Vance.

It features the engineered species utilized by the humans, which are fed on syrup in sacs.

Some features you have mis-remembered, not all of the engineered species are sentient.

For example, the transport vehicles are called "power wagons" but are "...great rectangular slabs of muscle, slung into a rectangular frame...Syrup sacs communicated with their digestive apparatus, wires led to motor nodes in the rudimentary brain..." When the protagonist drives one, he "...twisted the awake key, tapped the go button, and pulled a lever..."

The reference to sewing a sac occurs when the protagonist visits a group of humans who do not use the engineered species and rather disdain those who do.

From the side, another Nomad called in an offensively jeering voice, "You will sew a sac on our backs where you can pour your syrup, hey?"

There is a full summary at wikipedia here.

It's a great story from a great author, I envy you the pleasure of re-encountering it.

The story is mentioned on this stack in a question here, but it is not a story-id question.

It can be read at the internet archive here.

  • 1
    Excellent answer, given all the misdirections I managed to heap on the question. Thanks, I will read it asap
    – user108131
    Commented May 26, 2022 at 17:48
  • @user108131 thanks! I will edit your link into the answer. Commented May 26, 2022 at 17:50

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