The Jack Russell Terrier is a type of small, principally white-bodied, terrier that has its origins in fox hunting. The name "Jack Russell" has been used to describe a wide array of small white terriers, but is now most commonly used to describe a working terrier.
A Jack Russell Terrier is not the same as a Parson Russell Terrier, which is a breed recently created by narrowing the Jack Russell standard. The Parson Russell Terrier is principly a show dog, and is rarely found in the hunt field.
Appearance
A Jack Russell Terrier is a working terrier, and the most important physical attribute of a working terrier is not coat color, gait or expression, but chest size. If a terrier is too large to get to ground it is virtually worthless as a working dog.
The red fox is the traditional quarry of the Jack Russell Terrier, and the quarry pursued by the Reverend John Russell himself. Red fox may den in a wide variety of locations from old badger settes and drain pipes to building crawl spaces, old rabbit holes and groundhog dens, but in all cases the working Jack Russell must be small enough to get up to its quarry, which is to say a Jack Russell's chest should be no larger than that of the animal it is pursuing.Jack Russell Terriers are predominantly white (more than 51%) with black, tan, or tricolour markings commonly found on the face and at the base of the tail. Jack Russell Terriers have small V-shaped ears that should fold downward, and strong teeth with a scissor bite. The body shape is approximately square.
Jack Russell Terriers come in three coat types: smooth, broken, and rough. In all cases, the coat should be dense and not soft, feathery or linty. A smooth coated dog should be smooth coated all over, with a dense topcoat that is approximately 1cm long. A rough-coated dog should have a double coat with fur as much as 10cm long, and should be rough-coated over its entire body. A broken-coated dog is any dog with a topcoat of intermediate length, or a dog that is largely or partially smooth with longer hair on some parts of its body.
Jack Russell Terrier tails are straight, held high and upright. Traditionally, tails are docked to around five inches -- the length of a hand grip. It is not a serious fault to leave a tail a little long, but too short a tail creates a less useful dog in the field and a dog that looks poorly balanced.
Temperament
The Jack Russell is a working terrier. Terrier work requires a dog that will bark at prey so that the dog can be located underground and be dug out if necessary. As a result, Jack Russell Terriers are most definitely vocal dogs.
Jack Russell Terriers are also very intelligent, high-energy dogs – requirements of a working dog which must problem-solve in the field and work tirelessy against often formidable quarry.
Due to their compact size, friendly and inquisitive nature, and intelligence, Jack Russells are popular as pets. Prospective buyers should be aware, however, that while these dogs may enjoy sitting in a lap, they are not “lap dogs†– they are dogs that require training and regular and consistent exercise to maintain their temperament and to occupy their minds.
Jack Russells that are not trained on a consistent basis, or are not exercised regularly, may exhibit unmanageable behaviour, including excessive barking, escaping from the yard, or digging in unwanted places inside and outside the house. In America, several Jack Russell rescue networks have to work constantly to find temporary and permanent homes for Jack Russell Terriers whose owners could not meet these requirements for keeping these dogs as house pets. Prospective Jack Russell Terrier owners are advised to do their homework.
Most Jack Russell Terriers easily mingle with children, though they do not tolerate even unintentional abuse. Most are outgoing, and very friendly towards other dogs, but a good number show same-sex aggression issues. Some JRT's exhibit a Napoleon complex regarding larger canines that can get them into dangerous situations. Their fearlessness can scare off a larger animal, but their apparent unawareness of their small size can lead to a lopsided fight with larger dogs if not kept in check.
It is not uncommon for a Jack Russell terrier to be cat-aggressive, and homes with other small fur-bearing animals in them (pet hamsters, rabbits, guinea pigs, etc.) would do well to think through the ramifications of bringing a working terrier into the house.