I have seen snails, primarily on cotton, many times is my career.  My standard line has been that “snails do not cause economic damage”.  However, I’ve seen one cotton field this year (Bolivar area) and had a similar report of another in Lauderdale County where I think snails have actually contributed to reducing stands.  This is NOT slugs, which commonly can cause obvious feeding injury and sometimes reduce stands below acceptable levels.  Remember, snails have shells and slugs do not.

In the example above, there were huge populations of snails on seedling plants, in some cases the plant was entirely covered with hundreds of snails.  There really was little evidence of feeding, but it appeared some plants were literally suffocated and died from lack of sun and/or CO2 (pictured below).  Unfortunately, the treatment options are similar to slugs.  Baits such as Deadline-MPs may provide some control of snails, but unlike with slugs, I have no experience with this.  Frankly, usually by the time you can get and apply these baits, it is either too late or you realize you can live with what you got.  Insecticides will not work!