Rats are part of a larger mammalian family (called a superfamily) of rodents termed “Muridae” (taken from the Latin words for mouse: “mus” and “muris”). This superfamily includes a vast number of different rodent species including hamsters, gerbils, muskrats, lemmings, voles and many others. The Muridae superfamily is, in fact, the largest mammalian family, boasting over 700 species.
There are many species of rodents termed “rats” or containing “rat” in their name, which are not true rats. When applied to rodents, “true” refers to two species, the brown rat (also known as Norwegian rats (rattus norvegicus) and the black rat (rattus rattus). They are furred, four footed animals with elongated bodies and naked tails.
Rats and mice are taxonomically closely related; in practical terms, the differentiation between the two is size, rats are larger than mice. The ancient Romans acknowledged this in their naming of the two species, a mouse was “mus minimus”, a rat “mus maximus”. Rats in the wild tend to grow no larger than about 500 grams or 1.1 lbs.
Wild rats tend to live, on average, no more than a year due mostly to predation. This is in contrast to the lifespan of a pet or laboratory rats, which can live up to three years, given good care.
Male rats are referred to as “bucks”; females which have not mated are “does”; breeding females are named “dams” and baby rats are called either kittens, pups or pinkies. Collectively rats may be said to live in colonies, packs or a “mischief”.
Intelligence of Rats?
Rats are fully capable of “prosocial” or altruistic behavior; in an environment with a caged fellow rat and a food source, rats will invariably free their caged counterpart and then all share in the food.Rats are opportunistic and survive by scavenging. They have highly developed senses of smell and taste. They also have an undisputed ability to learn as evidenced in the wild by their ability to recognize and avoid new objects or devices in their environment; shun foods based on trial and error tasting; or to sidestep anything that has resulted in the death of another rat in the environment.
In terms of general intelligence (the “g factor”), or how acquired knowledge in one area is used in different circumstances and situations; the jury is still out. Some studies have shown rats do exhibit a high degree of “g factor”, while other experiments cast doubt on the hypothesis. In any event, rats may be considered highly adaptable, clever animals which are known for their ingenuity and boldness.
Relationship to Humans
Rats are considered commensal animals, that is, they exist in a relationship with another species in which they benefit and there is no effect on the other species. This other species just so happens to be us humans!
While a majority of human beings on the planet would vehemently reject the idea that rats are not harmful in their interactions with people, this classification of the relationship refers to overall impact on the species as a whole. Given all things being equal and under ideal situations, humans and rats can live in close proximity without humans being any the wiser or being harmed, while the rat benefits greatly from living in the vicinity with humans.
But what about The Great Plague?
Bubonic plague is caused by the bacterium “Yersinia pestis” which is thought to have spread beyond its starting point in Central Asia via the guts of rat fleas that infested the black rats that had always been unauthorized fellow travelers on human ships of commerce.Bubonic plague is often pointed out as a refutation of the rat-human dynamic being commensal. The Black Death did kill up to 50 percent of human life in Europe during the 14th Century; rats have long been blamed for this biologic catastrophe.
Disease and epidemic experts in the modern day feel that while this may well have been an important disease vector, it was not the only one. The massive spread of the plague cannot be explained away by rats and their fleas alone.
Filthy living conditions including sewage running in streets, overcrowding and the virtual lack of personal hygiene in the areas where the plague hit hardest facilitated the spread of all disease. Rat populations were not large enough to account for all the widespread diffusion of the disease; cold climates where fleas of any type could not survive were as heavily infected as those that were more congenial to flea infestation. These facts have influenced theories that have been put forth to explain the causes of the historic pandemic in recent years. In all likelihood, a “perfect storm” of several factors led to the disastrous epidemic, a unique combination that hopefully will not be repeated in the future.
Rats are responsible for humans contracting about a dozen diseases and illnesses; but statistically the problem populations are vastly outnumbered by those who present no risk to humans. Any sins of the rat in the spread of disease must be militated against the fact that laboratory rats (starting with a group of albino brown rats domesticated in 1895 at Massachusetts’s Clark University for the study of diet) have contributed greater understanding of human disease, genetics and drug effects.
There is little doubt that rats pose problems for humans in other ways. Millions of dollars’ worth of food crops is lost to rat infestations in the U.S. alone—in the world the losses may well be in the billions. Rats can cause damage to property, by gnawing through electrical wiring and thereby causing fires; by their characteristic gnawing and chewing on structures.
Overpopulation of rats in India has resulted in rampaging swarms of the animals devouring everything in sight, not unlike the proverbial plague of locusts. When rats are intentionally or accidentally introduced to isolated habitats such as islands, they pose definite dangers to native species and the environment in general; eradication of rat populations from islands is often the only solution to saving both.
Rats actively seek out human populations as easy sources of food and water, they like the same foods we do and are eager to next in the warmth and relative safety of our homes, business and farms.
Humans have had an undeniably long and troubled history with rats; their status as a pest species is not likely to change.