Wool-sucking and chewing is considered by animal behaviorists to be a type of obsessive-compulsive disorder in cats. Cats that engage in the behavior usually lack socialization early in life. Premature separation from their mother is also identified as an important predisposing factor.
Even after they have been weaned, kittens may continue to suck on wool, or another cat to seek comfort. They are even known to suck human ear or finger. Some cats even suck on a part of their body. Cats associate suckling their mother’s teat as a gratifying experience, and when they’re anxious or when exposed to stressors, they find comfort in sucking substitutes.
In many cats that display the behavior, wool sucking is an emotional outlet. However, there are rare occasions when it is associated with pica, wherein a cat eats stuff that is not considered food. They usually do this to try to satisfy specific dietary deficiency that they may be experiencing. To know more, visit your vet.