The word fox comes from Old English, which derived from Proto-Germanic *fuhsaz. This in turn derives from Proto-Indo-European *puḱ-, meaning ’thick-haired; tail’. Male foxes are known as dogs, tods or reynards, females as vixens, and young as cubs, pups, or kits, though the latter name is not to be confused with a distinct species called kit foxes. A group of foxes is referred to as a skulk, leash, or earth.
Foxes are generally smaller than other members of the family Canidae such as wolves, jackals, and domestic dogs. For example, in the largest species, the red fox, males weigh on average between 4.1 and 8.7 kg (9.0 and 19.2 lb), while the smallest species, the fennec fox, weighs just 0.7 to 1.6 kg (1.5 to 3.5 lb). Fox-like features typically include a triangular face, pointed ears, an elongated rostrum, and a bushy tail. Foxes are digitigrade, and thus, walk on their toes. Unlike their dog relatives, foxes have partially retractable claws. Fox vibrissae, or whiskers, are black. The whiskers on the muzzle, mystaciae vibrissae, average 100-110mm long, while the whiskers everywhere else on the head average to be shorter in length. Whiskers (carpal vibrissae) are also on the forelimbs and average 40mm long, pointing downward and backward. Other physical characteristics vary according to habitat and adaptive significance.
Fox species differ in fur color, length, and density. Coat colors range from pearly white to black and white to black flecked with white or grey on the underside. Fennec foxes (and other species of fox adapted to life in the desert, such as kit foxes), for example, have large ears and short fur to aid in keeping the body cool. Arctic foxes, on the other hand, have tiny ears and short limbs as well as thick, insulating fur, which aid in keeping the body warm. Red foxes, by contrast, have a typical auburn pelt, the tail normally ending with white marking. A fox's coat color and texture may vary due to the change in seasons; fox pelts are richer and denser in the colder months and lighter in the warmer months. To get rid of the dense winter coat, foxes moult once a year around April; the process begins from the feet, up the legs, and then along the back. Coat color may also change as the individual ages.
A fox's dentition, like all other canids, is I 3/3, C 1/1, PM 4/4, M 3/2 = 42. (Bat-eared foxes have six extra molars, totaling in 48 teeth.) Foxes have pronounced carnassial pairs, which is characteristic of a carnivore. These pairs consist of the upper premolar and the lower first molar, and work together to shear tough material like flesh. Foxes' canines are pronounced, also characteristic of a carnivore, and are excellent in gripping prey.
In the wild, the typical lifespan of a fox is one to three years, although individuals may live up to ten years. Unlike many canids, foxes are not always pack animals. Typically, they live in small family groups, but some (Arctic foxes) are known to be solitary.
Foxes are omnivores. The diet of foxes is largely made up of invertebrates such as insects, and small vertebrates such as reptiles and birds, and can include eggs and plants. Many species are generalist predators, but some (such as the crab-eating fox) have more specialized diets. Most species of fox consume around 1 kg (2.2 lb) of food every day. Foxes cache excess food, burying it for later consumption, usually under leaves, snow, or soil. Foxes tend to use a pouncing technique where they crouch down to camouflage themselves in the terrain, then using their hind legs, leap up with great force to land on top of their targeted prey. Using their pronounced canine teeth, foxes grip on to their prey's neck and either shake until the prey is dead, or until the animal can be disemboweled.
The gray fox is one of only two canine species known to climb trees; the other is the raccoon dog.
The male fox's scrotum is held close to the body with the testes inside even after they descend. Like other canines, the male fox has a baculum, or penile bone. The testes of red foxes are smaller than those of Arctic foxes. Sperm formation in red foxes begins in August–September, with the testicles attaining their greatest weight in December–February.
Vixens are in heat for one to six days, making their reproductive cycle twelve months long. As with other canines, the ova are shed during estrus without the need for the stimulation of copulating. Once the egg is fertilized, the vixen enters a period of gestation that can last from 52 to 53 days. Foxes tend to have an average litter size of four to five with an 80 percent success rate in becoming pregnant. Litter sizes can vary greatly according to species and environment – the Arctic fox, for example, can have up to eleven kits.
The vixen has four pairs of teats. Each teat has 8 to 20 lactiferous ducts, which connect the mammary gland to the nipple, allowing for milk to be carried to the nipple.
The fox's vocal repertoire is vast:
Whine - Made shortly after birth. Occurs at a high rate when kits are hungry and when their body temperatures are low. Whining stimulates the mother to care for her young; it also has been known to stimulate the male fox into caring for his mate and kits.
Yelp - Made about 19 days later. The kits' whining turns into infantile barks, yelps, which occur heavily during play.
Explosive call - At the age of about one month, the kits can emit an explosive call which is intended to be threatening to intruders or other cubs; a high pitch howl.
Combative call - In adults, the explosive call becomes an open-mouthed combative call during any conflict; a sharper bark.
Growl - An adult fox's indication to their kits to feed or head to the adult's location.
Bark - Adult foxes warn against intruders and in defense by barking.
In the case of domesticated foxes, the whining seems to remain in adult individuals as a sign of excitement and submission in the presence of their owners.
Canids commonly known as foxes include the following genera and species:
Several fox species are endangered in their native environments. Pressures placed on foxes include habitat loss and being hunted for pelts, other trade, or control. Due in part to their opportunistic hunting style and industriousness, foxes are commonly resented as nuisance animals. On the other hand, foxes, while often considered pests themselves, have been successfully employed to control pests on fruit farms while leaving the fruit intact.
The island fox, though considered a near-threatened species throughout the world, is becoming increasingly endangered in its endemic environment of the California Channel Islands. A population on an island is smaller than those on the mainland because of limited resources like space, food and shelter. Island populations, therefore, are highly susceptible to external threats ranging from introduced predatory species and humans to extreme weather. On the California Channel Islands, it was found that the population of the island fox was so low due to an outbreak of canine distemper virus from 1999 to 2000 as well as predation by non-native golden eagles. Since 1993, the eagles have caused the population to decline by as much as 95%. Because of the low number of foxes, the population went through an Allee effect; this is where at low enough densities, an individual's fitness decreases. Conservationists, therefore, had to take healthy breeding pairs out of the wild population to breed them in captivity until they had enough foxes to release back into the wild. Nonnative grazers were also removed so that native plants would be able to grow back to their natural height, thereby providing adequate cover and protection for the foxes against golden eagles.
Darwin's fox is considered critically endangered because of their small known population of 250 mature individuals as well as their restricted distribution. On the Chilean mainland, the population is limited to Nahuelbuta National Park and the surrounding Valdivian rainforest. Similarly on Chiloé Island, their population is limited to the forests that extend from the southernmost to the northwestern most part of the island. Though the Nahuelbuta National Park is protected, 90% of the species live on Chiloé Island. A major problem the species faces, therefore, is their dwindling, limited habitat due to the cutting and burning of the unprotected forests. Because of deforestation, the Darwin's fox habitat is shrinking, allowing for their competitor's (chilla fox) preferred habitat of open space, to increase; the Darwin's fox, subsequently, is being outcompeted. Another problem they face is their inability to fight off diseases transmitted by the increasing number of pet dogs. To conserve these animals, researchers suggest the need for the forests that link the Nahuelbuta National Park to the coast of Chile and in turn Chiloé Island and its forests, to be protected. They also suggest that other forests around Chile be examined to determine whether Darwin's foxes have previously existed there or can live there in the future, should the need to reintroduce the species to those areas arise. And finally, the researchers advise for the creation of a captive breeding program, in Chile, because of the limited number of mature individuals in the wild.
Foxes are often considered pests or nuisance creatures for their opportunistic attacks on poultry and other small livestock. Fox attacks on humans are not common. Many foxes adapt well to human environments, with several species classified as "resident urban carnivores" for their ability to sustain populations entirely within urban boundaries. Foxes in urban areas can live longer and can have smaller litter sizes than foxes in non-urban areas. Urban foxes are ubiquitous in Europe, where they show altered behaviors compared to non-urban foxes, including increased population density, smaller territory, and pack foraging.
Foxes have been introduced in numerous locations, with varying effects on indigenous flora and fauna.
Fox hunting originated in the United Kingdom in the 16th century. Hunting with dogs is now banned in the United Kingdom, though hunting without dogs is still permitted. Red foxes were introduced into Australia in the early 19th century for sport, and have since become widespread through much of the country. They've caused population decline among many native species and prey on livestock, especially new lambs. Fox hunting is practiced as recreation in several other countries including Canada, France, Ireland, Italy, Russia and the United States.
There are many records of domesticated red foxes and others, but rarely of sustained domestication. A recent and notable case is the Russian silver fox, which resulted in visible and behavioral changes, and is a case study of an animal population modeling according to human domestication needs. The current group of domesticated silver foxes are the result of nearly fifty years of experiments in the Soviet Union and Russia to domesticate the silver morph of the red fox. This selective breeding resulted in physical and behavioral traits appearing that are frequently seen in domestic cats, dogs, and other animals, such as pigmentation changes, floppy ears, and curly tails. Notably, the new foxes became more tame, allowing themselves to be petted, whimpering to get attention and sniffing and licking their caretakers.
Foxes, particularly red foxes, have been inhabiting and breeding in human-populated areas since the twentieth century. They have adapted well to these environments, taking advantage of man-made features such as houses and gardens to create dens. For sustenance, they take advantage of food thrown away by humans. In some cases, human residents will feed foxes that frequent their local area. In this sense, a benign relationship has been established in which foxes have become comfortable and amiable toward the humans who, while becoming their providers, do not much mind the presence of the foxes. However, for some, urban foxes have proven to be a nuisance due to their intrusion and destruction of private property. Urban fox control methods and laws vary regionally.
The fox appears in many cultures, usually in folklore. However, there are slight variations in their depictions in folklore. In Western folklore and also in Persian folklore, foxes are depicted as a symbol of cunning and trickery – a reputation derived especially from their reputed ability to evade hunters. This is usually represented as a character possessing these traits. These traits are used on a wide variety of characters, either making them a nuisance to the story, a misunderstood hero, or a devious villain.
In Asian folklore, foxes are depicted as a familiar spirit possessed of magic powers. Similar to Western folklore, foxes are depicted as mischievous, usually tricking other people, with the ability to disguise as an attractive female human. However, there are other depictions of foxes as a mystical, sacred creature, that can either bring wonder or ruin.
Nine-tailed foxes appear in Chinese folklore, literature, and mythology, in which, depending on the tale can be a good or a bad omen. The motif was eventually introduced from Chinese to Japanese and Korean cultures.
The constellation Vulpecula represents a fox.
In some countries, foxes are major predators of rabbits and hens. Population oscillations of these two species were the first nonlinear oscillation studied, and led to the now-famous Lotka-Volterra equation.