"The Roof Rat" (Rattus rattus)

There is apparently disagreement among pest control historians as to just when the rat arrived in Europe. Zinsser (1935) states: "De L'Isle believes that the black rat, Rattus rattus rattus, originated from Rattus rattus alexandrinus and that it did not become parasitic on human beings until the seventh century, and that prior to this time, it lived a wild existence, possibly in the Arabian deserts. Moreover, De L'Isle was of the opinion that the brown rat became domesticated at the time of the crusades, when it accompanied man everywhere by ship, and thus spread through the Mediterranean ports.

Another writer, Sambon (1924), heartily disagrees with some statements made by others and his criticisms are herewith shown: "From recent publications I noticed that naturalists and archaeologists continue to perpetuate the erroneous notion that the black rat (Rattus rattus) was unknown to the ancient Greeks and Romans, and that it came to Europe during the 12th century in the ships of returning Crusaders. On several occasions, during the last 20 years, I have endeavored to show that the black rat has inhabited Europe from time immemorial. To the ancients the rat was merely a mouse, and indeed, even the early medieval Bestiaries describe a Mus major (rat) and a Mus minor (mouse). I have drawn attention to the innumerable and excellent representations of rats in ancient Greek, Etruscan and Roman works of art, and especially to works portraying them in actions more appropriate to rat than mouse, such as gnawing ship cordage, etc.

The roof rat is a native of Southeast Asia. It followed the caravan routes across India into the eastern Mediterranean region and entered Europe about the time of the Crusades. During medieval times it was the common house rat in Europe during the outbreak of plague known as the Black Death. In the European area the roof rat has two distinct color phases: the black rat of Western Europe and the brown alexandrine rat common around the Mediterranean. When this species was carried to the Americas, however, this situation changed. These introductions into North America began well before 1750, and roof rats were well known throughout the French, English and Spanish colonies. Here the color phases from all parts of Europe were dumped together in the same ports, where they interbred freely. As a result, today in North America all the color phases can crop up in one population. Often a single litter of young roof rats will contain both black and brown animals. Roof rats may be wholly black or brown-backed with the belly varying from gray to cream-colored or white.

The roof rat is found comonly in seaports and in the Gulf states, and Dykstra (1950) notes this rat outnumbers the Norway rat nine to one in some parts of Texas. The roof rat also is a house rat. It may live in trees, shrubs and in vines on the outside walls of houses. As a rule, it does not live too close to man, although occasionally, especially during the winter, it will enter barns and the upper stories of houses. Brooks (1964) notes roof rats occur in sanitary sewers in California, and this occurs in Arizona as well. He also states (1966) dense growth of trees, shrubs and vines, woodpiles, sheds and accumulated yard rubbish all contribute to infestation by this rat.

Hamilton (1947) observes that if rats were not largely nocturnal animals, we would soon be apprised of their tremendous numbers. They usually become active "one-half hour after dusk, after the premises have become quiet." Williams (1948) adds, "Rats are not truly nocturnal, their apparent nocturnalism being an expression of their mode of self-defense, that is immediate retirement in the face of danger, into inaccessible and hidden retreats. When unmolested, rats roam about, seeking food, during any part of the day or night. That they are more frequently abroad at night is because their principal enemies are relatively inactive during the night hours." Chitty and Shorten (1946) observed well-fed rats are predominantly nocturnal, and hungry rats may feed during the day. Often it is the subordinate individuals in high density populations that are forced into the daytime foraging routine.