Wallowing is a comfort behaviour in which an animal rolls about or lies in mud, water, or snow. In ethology, the term is generally distinguished from rolling in dust, which is usually classified separately as dust bathing. The behaviour is widespread among mammals, with documented examples in domestic pigs, rhinoceroses, warthogs, elephants, bison, elk, deer, hippopotamuses, and tapirs.
Etymology
The verb derives from Middle English walwen (mid-13th century), meaning "to roll the body in mud, sand, etc.," also "to toss and turn in bed, flounder about weakly." This descends from Old English wealwian, "to roll, turn oneself over and over," from West Germanic *walwon, ultimately from the Proto-Indo-European root *wel-, "to turn, revolve." A figurative sense, "to plunge or remain in some state or condition," is attested from the early 13th century. The noun form is recorded from the 1590s as "act of rolling," and from 1841 as "a place where an animal wallows."
Functions
Many functions of wallowing have been proposed, although not all have been tested by rigorous scientific investigation. Proposed functions include:
- Thermoregulation — documented in domestic pigs, the great Indian rhinoceros, warthogs, and elephants. Domestic pigs lack functional sweat glands and are nearly incapable of panting, so they rely on wallowing in water or mud to cool the body.
- Sunscreen — suggested for pigs, warthogs, and elephants, where a dried coating of mud may protect the skin from solar radiation.
- Removal of ectoparasites — documented in the white rhinoceros, American bison, and warthog. Pigs may allow mud to dry and then rub against a tree or rock to dislodge parasites trapped in the dried mud.
- Social behaviour — in elk, European bison, and red deer, wallowing has been associated with male-male conflict and with reinforcing hierarchy and group cohesion.
- Scent-marking — some animals urinate in a wallow before entering and rolling in it, presumably as a form of scent-marking.
- Relief from moulting and biting insects, skin maintenance (preventing dehydration), camouflage, and play in young animals have also been proposed.
Wallowing is often combined with other behaviours: elephants frequently blow dirt over themselves after wallowing to create a thicker coating, and pigs commonly rub against trees or stones after leaving a wallow.
Documented species
In intensive pig farming, pigs are generally kept indoors on slatted concrete floors, which largely denies them the ability to wallow; animal welfare concerns have been raised on this basis, as wallowing appears to be strongly motivated behaviour in pigs.
The Sumatran rhinoceros spends a large part of its day wallowing; one 20-month study recorded 80 to 300 minutes per day spent in wallows by wild individuals. Captive individuals deprived of adequate wallowing have developed broken and inflamed skin, suppurations, eye problems, inflamed nails, and hair loss, and have eventually died.
Among deer, red deer and Père David's deer wallow frequently and create wallow sites in wet depressions that can reach 2 to 3 metres across and up to 1 metre deep, while fallow deer do not wallow; variation also exists between subspecies and breeds of red deer.
Figurative and psychological usage
In general English usage, the term carries figurative senses: to devote oneself entirely to something, to take unrestrained pleasure, to indulge oneself immoderately, or to become or remain helpless — as in the common expression "wallowing in self-pity." In psychology, the related but distinct concept of rumination refers to sustained, repetitive focus on negative thoughts and emotions.
Status
Wallowing is an established concept in ethology, with coverage in encyclopedic and scientific sources. Some proposed functions remain hypotheses that have not all been subjected to rigorous experimental testing.
