The weasel is a species of mustelid distributed from southern Canada throughout all the United States and Mexico, southward through all of Central America and into northern South America. The long-tailed weasel is the product of a process begun 5–7 million years ago, when northern forests were replaced by open grassland, thus prompting an explosive evolution of small, burrowing rodents.

The long-tailed weasel's ancestors were larger than the current form, and underwent a reduction in size to exploit the new food source. The long-tailed weasel arose in North America 2 million years ago, shortly before the stoat evolved as its mirror image in Eurasia. The species thrived during the Ice Age, as its small size and long body allowed it to easily operate beneath snow, as well as hunt in burrows. The long-tailed weasel's growth rate is rapid, as by the age of three weeks, the kits are well furred, can crawl outside the nest and eat meat. At this time, the kits weigh 21–27 grams. At five weeks of age, the kit's eyes open, and the young become physically active and vocal. Weaning begins at this stage, with the kits emerging from the nest and accompanying the mother in hunting trips a week later.

Facts About Weasels: Weasels are adaptable and live all over the world. For example, the long-tailed weasel lives in North America, while the tropical weasel lives in South America. Japanese weasels are found in habitats grasslands, forests, villages and suburbs across Japan. Mountain weasels are found in in central and east Asia and the African striped weasel is found, predictably, in Africa. The most common weasel is the short-tailed weasel. It can be found in North America, Europe and Asia, in regions as far north as the Arctic. Their homes include marshes, scrubs, hedgerows, alpine meadows, riparian woodlands and riverbank habitats, according to the International Union for Conservation of Nature and Natural Resources (IUCN).

As nocturnal animals, weasels sleep during the day and are active at night. Most of a weasel's time awake consists of hunting, storing excess food and eating. Their bodies don't store fat, so they need a constant supply of food to provide enough energy. In fact, the least weasel eats 40 to 60 percent of its body weight every day, according to the Nature Conservancy. Though weasels can dig their own burrows quite quickly, they sometimes take over other animals' burrows and make them their own. They have even been known to take over termite hills.

Weasels' diets usually consist of rats, mice, voles and rabbits. Frogs, birds and bird eggs are also on the menu, from time to time. Their small, thin bodies allow them to squeeze into tight spots to reach small prey. Females typically have one or two litters per year. They give birth to litters of up to 15 offspring, called kits, according to ADW. Gestation lasts about a month. However, the number of kits, the length of the gestation period, weaning age and sexual maturity varies with the species. For example, long-tailed weasels mate in mid-summer, but implantation is delayed and the egg does not begin to develop until March, making the gestation period about 280 days, according to ADW. Some species of weasel live up to 10 years, though many live three to five years.

Winter weasel being wiped out by predators because global warming has melted snow. Most weasels are listed as least concern by the IUCN's Red List of Threatened Species. There are a few exceptions. The mountain weasel and Japanese weasel are listed as near threatened because their population has had a significant decline. The Colombian weasel is listed as vulnerable because of "a continuing decline in population due to ongoing deforestation" and has estimated population of around 1,300 mature adults. In New Zealand, the weasel is considered an invasive species and a threat to native wildlife. The country plans to eradicate them by 2050, according to a 2016 Live Science article.