Glens were originally used for eradicating other animals such as rat, fox, badger, and otter, and also as a general-purpose farm dog for herding and family companionship. Unlike many other terriers, they are 'strong dogs' rather than 'sounders'—they were bred to work mute to ground, going silently into dens after their quarry rather than barking at it to alert their handlers. In hunting trials, which used to be required by many kennel clubs for championships, Glens were disqualified if they sounded at the quarry. For this reason, today they are among the quietest terriers.