Rats are so abundant that measures need to be taken to control their numbers, especially around human settlement, to avoid the spread of disease. Ratting is an effective form of pest control that can involve the laying of traps or the deployment of dogs. The dogs most commonly used for rat-catching are specially bred terriers.
The terrier group of dogs evolved in Great Britain through an objective to produce a dog that would instinctively dig the ground in search of burrowing animals such as rats, rabbits, foxes and badgers. The need for these tough, hard-working dogs ran parallel with the increase in industrialisation from the 18th century onwards in Europe and North America. Various breeds were created in accordance with specific skills required in different areas.
The 10- to 12-inch-tall cairn terrier was originally intended to control vermin numbers, being small enough to wriggle its way through rocks and crannies. It is nowadays superseded in popularity by the slightly larger Jack Russell terrier, which was originally bred to hunt foxes. They were small enough to enter drains, but big enough to run with hounds. Nowadays, Jack Russells are less commonly used in fox hunting, but are still adept rat catchers. Another ratter is the rat terrier, although it is not recognised as an official breed by the American Kennel Club.
Terriers are bold, tenacious and energetic dogs with an innate urge to tunnel for vermin. These attributes are especially embodied in the Jack Russell terrier. They are also extremely quick and agile and will bark incessantly to disturb their prey and frighten it from its burrow. Jack Russells have teeth as large as those of a German shepherd--a dog at least 27.2kg. heavier--which enable them to kill rats by simply grabbing and shaking them.
Terriers relish the opportunity to hunt rats and mice. They are so effective that their owners can offer professional rat-catching services. There are no laws against hunting rats, because their numbers make them an urban pest, and the dogs can actually help local governments save money on pest control. Moreover, the use of dogs as an alternative to rat poison has been noted as a preferred option for farmers worried about their livestock swallowing poison and alleviates the same risk to wildlife.
A city overrun with rats is a problem for a number of reasons, some often unrecognized. Apart from the obvious threat to humans of disease spread onto food, another potential risk is rat-bite fever. This can be life-threatening if not treated with antibiotics and can be caught from a bite or scratch or just handling an infected rat. It is fortunately rare, but it can also be passed onto a dog that has been in contact with an infected rodent.
Terriers are skilled enough to be rarely bitten by rats. Nor do they eat their prey; one bite with vigorous shaking usually suffices to kill the rodent. Not digesting the animal reduces the risk of poisoning. Furthermore, a dog will normally have received its shots to minimise any concern of contracting a disease while rat hunting.