CBC Radio 1 “Quirks and Quarks” has a Question/Answer show, where 10 questions sent in by listeners are picked, and 10 experts answer them. One question was, “Is it true that cat’s whiskers only grow as long as their bodies are wide?”
It was answered by a research veterinarian at U of Saskatchewan’s Vet College. The answer was, in general, yes, although there is some plasticity to the length that they will grow. They have receptors that can detect how wide an opening is, as well as some information as to the make-up of the object’s sides (smooth/rough, etc.). A cat with it’s whiskers cut off can negotiate a maze of openings just as well as a cat with whiskers in daylight, but will take significantly longer in darkness. Whiskers are shed and replaced over time just like other hair on the body. Whiskers on congenitally blind cats are a little longer (on average) than those of a sighted cat. Whiskers can grow a little longer on a cat that grows larger (wider) and heavier over its lifetime but not by very much.