Bacteria that produce thick walls around themselves are called endospores.

Here's why:

* Endospores are dormant, tough, and non-reproductive structures produced by some bacteria. They are formed within the bacterial cell and are essentially a survival mechanism.

* The thick wall surrounding the endospore is made of peptidoglycan, a tough, protective material that helps the bacteria survive harsh conditions like heat, radiation, chemicals, and lack of nutrients.

* This thick wall makes endospores highly resistant to destruction, which is why they are difficult to kill.

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