“Nature has sent the rats to our homesteads by thousands, and farmers are being eaten off the face of the earth by them.”
This quote from H.C. Bartley (1911) appeared in his book Studies in. After a career in the art of catching rats and rabbits in England for a living, he wrote this book as a reference for teaching his profession at schools.
He dedicated his book to the headmasters of Eton, Harrow, Westminster, and Rugby. Alas, given the dearth of specialists in rodent management in Europe, it appears that the book did not become prescribed reading.
The human fascination with rats is highlighted by the recent republication of this book and a new bestseller published in 2005 simply called Rats.
The latter is the story of Robert Sullivan, a journalist who spent a year observing the secret lives of rats in Harlem in New York City. He punctuated his observations with historical accounts such as how rats catalyzed major changes in the living conditions of Harlem tenants after many other efforts, including tenant strikes, failed.
Rats and mice, animals that have played a central role in human life for thousands of years, are arguably the most important family of mammals. There are over 2,270 species of rodents (defined as animals that have continually growing incisor teeth and no canine teeth) and 42% of all mammal species are classified as rodents.
They are the ultimate mammalian weed, living in almost every habitat on Earth, and adapting well to environments significantly altered by humans.
Rodents have two major impacts. The first is the substantial pre- and postharvest losses they cause to agriculture. The second is as carriers of debilitating human diseases.
Rodents have an enormous economic impact on stored grain in developing countries. Rats need to eat 10–15% of their body weight each day and they contaminate much more rice than that with their droppings. In one year, 25 adult rats would eat and damage about half a ton of grain and produce about 375,000 droppings!
Good data on postharvest losses caused by rodents are sparse; however, reports of up to 20% postharvest losses of rice are not unusual. In 1991, a study in central Punjab in Pakistan found that for every person living in a village there were 1.1 house rats. Extrapolating to the national level, it was estimated that 0.33 billion metric tons of cereal (rice, maize, and wheat) were consumed annually by house rats in Pakistani villages.
This is a conservative figure because rodents damage more food than they consume and cause major damage to the structure of grain stores, which in turn leads to increased weather.