Lagidium is a genus of rodent in the family Chinchillidae. It contains the following species:
- Northern Viscacha (Lagidium peruanum)
- Southern Viscacha (Lagidium viscacia)
- Wolffsohn's Viscacha (Lagidium wolffsohni)
- Lagidium ahuacaense - a new species from Ecuador described in June 2009.
Members of this species are medium to large-sized rodents which also looks remarkably like a long-tailed rabbit. Soft dense fur covers its body, from the tips of its elongate fur covered ears, edged with a fringe of white fur to the end of its long, curled tail. Their tails are bushy and can range up to about 1/3 of the length of its body. The forelimbs are relatively short, while the contrastingly long and muscular hind-limbs enable it to run and jump with ease. However, the number of digits on the hind feet is reduced to 4 (apparent in Chinchillas as well). The color of its fur varies seasonally and with age, but generally the upper parts are grey to brown, with tints of cream and black, while the under-parts are pale yellow or tan. However, contrary to the former statement, it has been stated elsewhere that they have pale yellow or grey upper parts, and a black tail tip. They weigh up to 6.6 lbs (3 kg) and have fairly delicate incisors in which the enamel of the incisors are not colored.
L. peruanum are diurnal species that are active throughout the year. They leap among rocks and performs a series of whistles and trills associated with warning. Colonial structures are composed of small family units of two to five individuals in a subdivided colony that can be as large as 75 animals.
L. viscacia are also diurnal and are most active near sunrise and sunset. They spend the day on perches, grooming and summing themselves. They are adept at moving over rocky surfaces and do not hibernate.
In northern viscacha (L. peruanum), males tend to be promiscuous. The gestation period for the female is 140 days, and the usual litter size is one. It is viviparous and lactation takes about eight weeks. In Peru, mating takes place from October through November. Both female and male sexual maturities are reached after one year and weaning has been found to occur after 59 days.
In southern viscacha (L. viscacia), mating occurs from October through December. After a gestation of 120–140 days, a female gives birth to a single, precocious (having developed certain abilities or proclivities at an earlier age than usual) young. The young are born fully furred, with their eyes open, and are able to eat solid food on their first day of life.