Laying them directly on the ground should be avoided. Laying them down on a wet towel prevents much of the slime coat from being removed. Removal of the slime coating does make them more susceptible to diseases until the slime coat is replenished. Luckily they start to replenish the slime coat as soon as it is lost. They also are continually replenishing, refreshing this slime coat for the duration of their lives.