Lemmings are species of small rodents that belong to several genera within the subfamily Arvicolinae. They inhabit various locations within the Arctic Circle, although some of them venture as far south as the United States. The lemming's characteristics are well suited for their frigid habitat; they have thick, long fur, with small features to retain heat and sharp nails for digging through the firm tundra. Another distinct trait is the lemming's ever growing teeth, a characteristic of rodents. These creatures hold a key role in their ecosystems, as they fall prey to numerous predators; thus they control the ecological balance of the tundra. Despite their short life span, lemmings reproduce at a rapid rate, periodically having 'high peaks' in population--something that their predators depend on. Lemmings are well known for these fluctuations in population; however, several misconceptions have been drawn from them. One of the main myths about lemmings is that they commit mass suicide, but this is nothing more than a misunderstanding of the lemmings' behavior in response to their environment.
All members of the taxonomic tribe Lemmini share several key characteristics. The most easily recognized features are the lemming's long, soft fur, short legs and tails, and dark beady eyes.  Lemmings also possess sharp nails, attached to four tiny furry feet. The front feet are strong, with the nails providing traction to allow the animal to dig for food or build a nest. A lemming's ears are rather small in comparison to the rest of their head; they are almost covered by the lemming's long fur.  Like other members of the suborder Myomorpha, a lemming's keenest senses are its hearing and smell.   Another key characteristic of lemmings are their ever growing incisors. Like all rodents, a lemming's teeth continue to develop throughout its lifetime. This trait enables the lemming to consume tougher grass and other forage, a food source that is only available because of the lemming's unique teeth. As a mammal, a lemming is endothermic (warm blooded), meaning it generates its own body heat.  Since all lemmings live in the northern regions of the world, this is a necessary characteristic for survival. However, the design of the lemming's body also helps it stay warm in its cold environment. Along with its thick fur, a lemming's appendages, such as its ears and feet, are small; this results in a lesser amount of surface area for the cold temperature to come into contact with its body. In addition to this characteristic, the lemming's rounded shape lets the blood to flow easier and faster to the other parts of its body, allowing for more efficient heating. 
Each species in tribe Lemmini has unique characteristics that distinguish one type of lemming from another. One clear example of this is size. A lemming's weight ranges from 30 to 112 grams (1.1 to 4.0 ounces), and its length can be between 7 to 15 cm ( 2.8 to 5.9 in).  Members of the genus Lemmus, also known as "true lemmings", are the largest of the tribe, measuring 10 to 13.5 cm (4 to 5 ½ in), including a 12 to 26 mm tail. They possess a heavy coat of fur and are rather stout, weighing an average 78 grams.  One member of the genus Lemmus, the Norway lemming (Lemmus lemmus) is noticeably different from other rodents because of its distinctly colored fur. The yellow, brown and black are contradictory to the usually plain colors of other rodents, who try to hide themselves from predators by blending in with their environment. It has been suggested that this trait adds to the lemmings defense of aposematism (warning display against predators).  Another species, the North American Brown lemming (Lemmus trimucronatus), uses the seasonal changes of its fur colors to conceal itself in its surroundings; their usually reddish-brown fur sometimes changes to gray in the summer.  A more obvious example of camouflage is exhibited by the Collared lemming (Dicrostonyx gruenlandicus), as it is the only true rodent to turn white during the winter. During this season, the Collared lemming's front third and fourth claws grow longer, acting like shovels to dig through the compacted snow and ice.  The Northern Bog lemming, (Synaptomys borealis) is the smallest lemming species, weighing just over an ounce.  This type of lemming has grooved teeth--a characteristic which excludes it from the group of "true lemmings." 
The life of a wild lemming is fairly short, only lasting one to three years. This brief lifespan is a result of various factors, including the harsh living conditions and natural predators to whom lemmings easily fall prey.  The lemming's breeding season is also short; however, within this period numerous lemmings can be produced.  The population density of lemmings influences length of the summer breeding season. When population numbers are low, breeding continues into September; when numbers are high, the breeding season may end as early as July. Lemming species seem to only breed during the summer and occasionally the winter--which is an amazing feat if accomplished considering all the risks of producing offspring in such cold temperatures. 
Despite their short lifespan, lemmings have the capability to produce a significant amount of offspring. Although specific conditions may vary between different species, there are basic characteristics they all share. A female reaches sexual maturity at a very young age--around 30 days old.  Some are able to breed even sooner at two to three weeks. Female lemmings have the ability to breed merely one day after giving birth; this fact aids in increasing the lemming population.  The female gestation (pregnancy) period lasts about three weeks. Baby lemmings are typically born in burrows dug under the snow, in order to keep them warm. The babies feed on milk until they have enough strength to find food on their own, which is usually after about 21 days.   Newborn lemmings weigh only a little over one tenth of an ounce (3 g). After eleven days, they open their eyes; after fifteen days they can walk.  Young lemmings experience their most rapid growth period between their fifth and twenty-second day. After this, their growth rate declines and evens out around 40 days old.  One female can have up to seven litters in a year, with an average litter size of seven young. In general, there are more females in one litter than males.   All of these factors contribute to the fluctuating population of lemmings.
Although all lemmings live in the arctic and northern regions, they are found in various locations across the globe, with each genus having slight differences between their ecological niches (an organism's relationship to and effect on its habitat).  There are almost 30 species of lemming on or in the Arctic Circle, stretching from Alaska to Siberia.  For example, the Norway lemming, true to its name, inhabits Scandinavia. Other members of the Lemmus genus, such as the Brown lemming, live in northern Europe and North America, including most of Alaska. Collared lemming species belonging to the genus Dicrostonyx also live in parts of Alaska, as well as Canada, Greenland, Europe, and Asia.   Species of the Synaptomys genus, known as Bog lemmings, inhabit the marshy regions of North America, going as far south as the northern United States--even Washington. The Myopus genus contains wood lemmings, which live in the swampy coniferous forests of northern Eurasia, as well as parts of Mongolia.   Most of these habitat ranges are locations of permafrost (soil that is always frozen). Because of this, lemmings are unable to dig deep burrows, even in the summertime. However, in the places where there's plenty of water in the soil, the freezing and thawing creates ridges and depressions that are used for burrows and tunnels. During the winter, lemmings construct rounded nests, lining them with shredded grasses, sedges, feathers, and even musk ox wool.   Instead of hibernating throughout the harsh arctic winter, lemmings search for food in the space between the soil and the snow, known as the subnivean space.  Lemmings eat a variety of food, including grass, seeds, bark, sedges, bulbs, and insects.  Because the food lemmings obtain does not have much nutrition, they must acquire large amounts. A lemming can spend up to six hours a day foraging for food; they take breaks in their burrows under the snow.  These burrows consist of many tunnels and pathways to and from the nest.  Lemmings can have different types of "rooms" in their burrow system, such as for resting, nesting, and even one for the bathroom. 
Lemmings play a large and significant role in their ecosystems. Because they are a major source of prey for arctic predators, lemmings "control the rhythm of life on the tundra".   Lemmings have several predators, including snowy owls, hawks, wolves, arctic foxes, weasels, ermines, gyrfalcons, and jaegers.    These predators depend heavily on lemmings. It has been observed that arctic foxes and snowy owls rarely have surviving young, except during a "lemming year"--a year at which the lemming population reaches a peak of high density.  Lemmings are famous for having these cycles of extremely high and low populations every three to five years, known as "cycles." When conditions are favorable, the lemming population rises drastically; this abundance of lemmings usually lasts no longer than a year. However, this increase in number attracts predators, and the population suffers death. Along with the now increased predator population, the lemmings are not able to sustain themselves because of their vast numbers. After some time, the population plummets to extremely low levels. During this low density population period, generally one to two years, the predators who only eat lemmings either move elsewhere or die. The severe scarcity of lemmings in the "low peak" of the cycle sometimes calls up the question of extinction; other rodents are known for having population booms, but none of them can compare to the remarkable shortage of lemmings during these times. However, recovery has continued to occur, with the eventual successful breeding of the lemmings. Since lemmings burrow under the insulating snow, the weather plays a part in the recovery process by keeping the young lemmings warm and alive. The vegetation of the tundra is also affected by the lemming population cycles, as the animals often overgraze. The size of lemming gatherings for grazing during population peaks are so enormous they can be seen from satellites. The vegetation is given a chance to grow back, however, during the low peaks in the cycle--thus starting the process all over again. Scientists have not been able to determine the exact cause for these dramatic population fluctuations. They are probably a result of predation, food quality and quantity, weather, or genetic changes in lemmings. Humans are generally not considered a threat towards the species, except when the creatures are around villages or industrial sites. Also, even though lemmings are known to carry parasites and experience several infectious diseases, few lemmings die of these causes.  So while the reason for these drastic cycles remains unclear, scientists do know that investigation is needed, because the smallest mammals of the high arctic are the key to understanding and predicting the arctic food web dynamics.  
Misconceptions of Lemmings
Lemmings have been a subject of misconception for several centuries. Nearly 500 years ago, in the 1530s, a geographer named Zeigler of Strasburg proposed a theory that lemmings fell out of the sky during stormy weather. This idea resembled the folklore of the Inupiat of western Alaska, as well as legends from the eastern Canadian Arctic and Scandinavia. In fact, one of the native names for lemming is "kilangmiutak"--meaning 'one who fell from the sky.' This legend may have come from the sudden appearance of lemmings during the spring of a population peak. However, this theory was opposed by the findings of a natural historian named Ole Worm, whose published dissections showed that lemmings were anatomically similar to most rodents.
Another popular misconception of lemmings is that they commit mass suicide during migration. This idea has been advertised by a combination of comics, staged documentary films, video games, and commercials. One of the main statements is that lemmings will sometimes reach the ocean on their migration route, and simply jump off into the water, either dying immediately or eventually exhaustion. Thus, lemmings are often used as a metaphor for people who follow the crowd without question, into situations with dangerous or fatal consequences. Another myth states that older lemmings leap off the edge to allow the younger generation full access to food and shelter.  However, there is a different explanation for this behavior than just saying lemmings are senseless and foolish. The truth is that lemming death does occur, but not as a result of mass suicide. During population peaks, lemmings become restless, and scatter in all directions to look for food. These large groups, driven by strong biological urges, push through several obstacles in their way--including rivers, lakes, and even seas or the ocean. Despite being good swimmers, many lemmings end up drowning as they reach their physical limits, and in some cases are even eaten by trout.  Individual lemmings are also often seen on lake or sea ice up to 55 kilometers from land because of their drive to search for food or new homes. Although it may seem that this 'migration' is a structured and regular behavior, lemming 'migrations' are actually not oriented in nature; the lemmings simply move to fit their needs--with the unfortunate but accidental casualties.  In fact, the lemming population crash every few years is mostly the result of predator increase. Another supporting factor to this reasoning is that there is no authentic account of mass lemming migration and deaths from the North American Arctic. It would be strange that the natives had never witnessed this act if the myths were true. In conclusion, all though the idea of suicidal lemmings has been popularized by the media, they are merely misconceptions of their behavior. Although scientists do not fully understand why lemmings would go to such extremes like running onto sea ice, they believe that the social upheaval of spring and the effect of the breeding season contribute to their actions.
A video showing that despite their small size, lemmings are not afraid to show aggressive behavior and even attack a human. This is also an example of aposematism.
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