What function were Yorkshire Terriers originally bred for by working-class mill workers?

Catching rats in the clothing mills and mines

The initial development of the Yorkshire Terrier breed in Yorkshire, England, during the mid-19th century was directly tied to necessity within industrial settings. Working-class mill workers were responsible for breeding these dogs specifically to control vermin populations. Their small size was not merely an aesthetic trait but a functional advantage, allowing them to efficiently access and clear small crevices and tight spaces within the clothing mills and mines where rats were abundant. This historical purpose firmly grounds the breed within the working traditions often associated with the Terrier Group, highlighting a significant divergence from their current status as primarily companion animals.