Working terrier
[6] Working terriers can be no wider than the animals they hunt (chest circumference or "span" less than 35cm) in order to fit into the burrows and still have room to maneuver.
The most critical physical attribute for a working terrier is a small chest size which facilitates navigation through narrow underground tunnels.
The optimal chest size varies depending on the dimensions of the tunnel system; generally, smaller dogs are more effective as they can reach their quarry without the need for extensive digging and without significant fatigue.
This can lead to a condition where the dog is trapped by the accumulated soil, making it extremely challenging to escape the tunnel without assistance, particularly if it is unable to turn around.
Other important requirements of a working terrier are essential gameness, a good nose, and the ability to problem-solve to avoid coming to harm underground.
A wide variety of game is hunted below ground with terriers, including red foxes, groundhogs (also known as woodchucks), raccoons, opossums, nutria (also known as coypu), and European and American badgers.
[10] Terrier work is not a very efficient way of hunting vermin, though in 2006, some 258 members of the Royal College of Veterinary Surgeons argued that it is a comparatively humane way to reduce fox numbers and is quite selective.
The inefficiency of terrier work means that, unlike poisons and traps, there is no danger that a species can be wiped out over a large area and little chance that an adult will be terminated with an unseen young still in the den.
Though inefficient, a team of terriers, when coupled with an enthusiastic digger, can control red foxes, raccoons, and groundhogs on small farms where their presence might be a problem for chickens, geese, wild bird populations, and crop production.
Because terrier work is selective, animals can be dispatched, or else they can be moved and relocated to nearby farms, forests, or waste areas where they will do no harm.
Vast expanses of enclosed open spaces proved perfect for mounted fox hunting, a sport that had arrived in the UK from France in the late 17th century.
Both Darwin's book and the first dog show drew much of their inspiration from the rapid "speciation" of new livestock breeds that had first begun with Robert Bakewell's efforts to control sire selection.
From these two roots spring a variety of Kennel Club dogs and every type of working terrier commonly found in the field today.
The tools used for terrier work have essentially remained unchanged for more than 400 years: a small-chested and game-working terrier, a good round point shovel, a digging bar, a brush hook to clear away hedges and brambles, fox nets, water for the dog and digger, a snare to remove the quarry, or a gun or blunt instrument to dispatch it.
The League Against Cruel Sports states that distressing and prolonged deaths occur during the digging out or flushing out of foxes, and serious injuries can be sustained by dogs.
