Rodents are members of the order Rodentia, which is the largest order of mammals.
There are about 2,280 rodent species which is about 40% of all mammal species.
Rodents are extraordinarily diverse in their body shapes, diets, and lifestyles.
They are found in vast numbers on all continents except Antarctica.
Ecologically, they are incredibly diverse. Some species spend their entire lives above the ground in the canopy of rainforests; others seldom emerge from beneath the ground. Some species are highly aquatic, while others are equally specialized for life in deserts.
Many rodents have an average life span of 1 to 4 years, but some larger rodents such as beavers and porcupines can live over 20 years. The oldest recorded rodent was a Sumatran crested porcupine that lived 27 years and three months.
Well-known rodents include mice, rats, squirrels, prairie dogs, chipmunks, chinchillas, porcupines, beavers, guinea pigs, hamsters, gerbils and capybaras. Rabbits, hares, and pikas, whose incisors also grow continually, were once included with them, but are now considered to be in a separate order, the Lagomorpha.
Most rodents are small animals with robust bodies, short limbs, and long tails.
Rodents range in size. The largest species is the capybara, which grow up to 134 cm (4.4 ft) in length, and weigh up to 66 kg (146 lb). The smallest rodent is the Baluchistan pygmy jerboa, which averages only 4.4 cm (1.7 in) in head and body length, with adult females weighing only 3.75 g (0.132 oz).
Rodents are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. They use their sharp incisors to gnaw food, excavate burrows, and defend themselves.
Rodents generally have well-developed senses of smell, hearing, and vision. Nocturnal species often have enlarged eyes and some are sensitive to ultraviolet light.
Many species have long, sensitive whiskers or vibrissae for touch or “whisking”.
Some rodents have cheek pouches – a specific morphological feature used for storing food and is evident in particular subgroups of rodents like kangaroo rats, hamsters, chipmunks and gophers which have two bags that may range from the mouth to the front of the shoulders.
Rodents may be diurnal, nocturnal, or sometimes active part of the day and night.
A wide variety of shelters are used or constructed; these range from tree holes, rock crevices, or simple burrows to hidden nests on the forest floor, leaf and stick structures in tree crowns, mounds of cut vegetation built in aquatic environments, or complex networks of tunnels and galleries.
Most rodents are herbivorous, feeding exclusively on plant material such as seeds, stems, leaves, flowers, and roots. Some are omnivorous and a few are predators.
Many rodents are food hoarders. That means they’ll take more food than they can eat so they can hold on to it for later. Many will eat some of what they find, then bring the rest along so they can hide it near where they live.
They tend to be social animals and many species live in societies with complex ways of communicating with each other.
Rodents may be active all year or enter periods of dormancy or deep hibernation.
Breeding time and frequency, length of gestation, and litter size vary widely, but two of the most prolific are both associated with humans. The brown rat can give birth to litters of up to 22 offspring, and the house mouse can produce up to 14 litters annually. Population size may remain stable or fluctuate, and some species, most notably lemmings, migrate when populations become excessively large.
The word “rodent” comes from the Latin word rodere, meaning “to gnaw.”
The fur of some rodents is an important product. The trapping of beavers for their fur played an important part in the history of North America. Some other rodents are also trapped for fur in the wild, while the chinchilla of South America is raised for its fur.
Chinchilla has very valuable fur. In fact, when its size and weight are considered, the fur is the most valuable in the world. Coats made of wild chinchilla pelts have sold for up to $100,000. It may take up to 400 pelts to make such a coat.
After humans, mice are the best-studied mammalian species in terms of their biology and genetics.
Squirrels help maintain and spread forests – they don’t dig up all of their buried nuts, which results in more trees!
Some rodent species have very high metabolisms, so they need to eat around 20 times a day!
An adult mouse has a heart rate of 632 beats per minute (plus or minus 51 bpm). A human heart only beats 60 to 100 beats per minute.
Few strictly arboreal species glide from tree to tree supported by fur-covered membranes between appendages.
Flying squirrels can glide up to 90 meters (300 feet), steering with their tail, and landing on tree trunks, gripping it with all four feet. They can make 180-degree turns while gliding.
Some species of rodents are expert at navigating the world in the dark using their sense of touch. They rhythmically brush and tap vibrissae (whiskers) against objects to determine object size, shape, orientation, and texture. This behavior is called “whisking.”
The prairie dog are named for their habitat and warning call, which sounds similar to a dog‘s bark. The name was in use at least as early as 1774.
As documented by fossils, the evolutionary history of rodents extends back 56 million years to the Late Paleocene Epoch in North America.
The largest rodent ever recorded, Josephoartigasia monesi, lived some two to four million years ago, during the Pleistocene and Pliocene epochs; by some estimates it grew to a length of about 3 metres (10 feet) and weighed nearly 1,000 kg (2,200 pounds).
From earliest times, rodents have been eaten by humans. Although the flesh of all species is edible, rodents are not an important food source in the world today.