Of Climate, Mice, and Men

Michael H. Glantz
25 August

The United States has an estimated
1.25 billion rats and they cause at least
$19 billion in damage a year. Worldwide,
3.5 million rats are born every day.


Of Climate, Mice and Men

Writing about mice, rats and other rodents --- what they are and what they do --- is a difficult thing to do for a non-expert on rodents. There are billions of them on the face of the Earth and many of them interact with settlements in negative ways. They are disease bearers as are their fleas and other parasites. They are linked to hantavirus, lassa fever, the plague, among other diseases. People in developing countries and poor people in industrialized and agricultural societies are most at risk to negative interactions with rodents. They are most likely to contract diseases from them in various ways. They are the ones whose food supplies are likely to be most accessible to rats and mice.

The focus here is on mice, rats and other rodents and their impacts on grain production. It is widely known that rodents eat large amounts of grain (wheat and maize for example) while much of that grain is in storage facilities. The lion's share of attention and research funds goes to improving crop yields and crop production. Considerably less (though I do not have the numbers) goes to research on ways to reduce grain losses once they have been harvested and stored. If the estimates of experts are anywhere near correct (up to 25% per year's harvest), then the large percentages of post-harvest grains lost to such pests can be sharply reduced. The issue deserves a lot of attention in Africa as well as on other continents.

Of climate and man

Climate variability, extremes and change have direct and indirect costly impacts on society. Innumerable case studies throughout the history of humankind show that societies, nomadic as well as sedentary, industrialized as well as agrarian, recent as well as past, have been in constant conflict with atmospheric processes. Ingenuity has enabled many societies to deal with the extremes, anomalies and changes as best they could. Societies have developed all kinds of ways to cope with the climate characteristics in their region. For example, they have developed air conditioning, refrigeration, irrigation techniques, fertilizers to enhance food production, transportation and even storage facilities as ways to "beat" the natural constraints imposed on them by their regional climate conditions.

Humans have not been the only ones to develop coping mechanisms in the face of a variable if not hostile climate. Rodents and other organisms too have identified pathways to ensure their survival in the natural environment. Rats and mice have learned how to benefit from the agricultural production efforts of humans. Drought-plagued food production as well as abundant harvests are conditions to which rat populations have learned to adapt. Where rodent and human populations come together, it is often the rodents that win: they take a hefty share of the harvest in the post-harvest period. They are the bearers of diseases feared by humans. Under a relatively stable climate regime, we have come to some sort of an awareness of rodent populations, their behavior, their habitats, and their infestations in the built and rural environments. However, global warming of the atmosphere and its regional implications will likely impact the validity of that current understanding. An article in Frontiers in Ecology and the Environment (2003, Vol. 1(7), www.frontiersinecology.org), states

Climate change is likely to change the length of the breeding season and increase the variance and/or change the mean precipitation. ... In fact, climatic change combined with changes in agriculture technique might put us at a competitive disadvantage to mice and rats.

Rising human populations, especially in urban settings, and the demand for increases in food production capability, in addition to increases in rodent populations in a warmer environment, demands increased attention to the various threats that rats and mice pose, for example, for food availability and human health in the future decades.

Of climate and mice

It is well-known by people who cultivate the land that climate has an influence on the population and behavior of grain-eating mice and other rodents. When crops in the field are abundant, a major increase in the rodent population takes place. Under such conditions, mice and rats become fat and happy. There is a significant loss of grain to rodents in time of plenty, but it is of little concern because there is still plenty of grain to sell at affordable prices in the markets and bazaars.

Under drought conditions, when crops in the field become sharply reduced, the rodent populations tend to become more aggressive in their search for food, not only in homes and grain storage facilities but also in the open fields. The drought of the early 1970s in the West African Sahel generated a lot of concern about rats that were eating the grain right off the crops in open fields, having been driven like local inhabitants to the edge of extreme hunger.

Thus, rodents pose a major problem for people. "Rodents are of major economic importance, primarily as consumers of the grains that are the basic foodstuff for humankind. It has been estimated that rats and mice destroy up to one-third of grain crops under conditions of heavy infestation. Burrowing rodents may damage root crops." (www.the-piedpiper.co.uk/th1.htm)

There are many examples of rodents consuming various types of grain around the globe. In Southeast Asia, for example, the Vietnam government considers the rat one of its major foes. They banned the killing of cats and snakes because they kill rats. The estimate in Vietnam is that "rats destroy hundreds of thousands of hectares of rice and grain fields" (www.terrierman.com/vietnam.htm).

The IRRI (International Rice Research Institute) has a website that focuses on non-chemical methods for the control of rodents that consume rice. "Many rodents cause problems in rice. The main pests are the "rice field rat," the black rat, and the lesser bandicoot rat. Various mice can also cause problems." The site also notes that the black rat is a major post-harvest pest, referring to the invasion by rodents and mice of grain storage facilities. Depending on a country's specific grain storage structures, as much as 25 percent of the post-harvest storage can be lost to them. Humidity, microorganisms, insects and birds, along with rodents, add to the estimated losses in stored grains.

The Rat Trap:

The following six paragraphs and images are taken directly from an interesting website (journeytoforever.org/at_rats.html):

1. It has been estimated that total crop losses caused by rodents, mostly rats, each year would be enough to feed 200 million people, nearly as many as the population of Indonesia. That's probably a low estimate, and post-harvest damage is about the same again.

2. In Southeast Asia rice crop losses due to rats are at least 15%: it's not unusual for farmers to report 15-30% losses, and losses can be as high as 50% or even 100% in a bad year.

Bandicoot Rat

3. In Indonesia, rats are the number one pre-harvest pest of rice, with about 17% of the harvest lost each year -- enough rice for 20 million Indonesians. In Laos, rodents are the second most important agricultural pest in mountainous regions, and the one over which farmers feel they have the least control. Rodents are one of Vietnam's top three agricultural problems.

4. Southeast Asian farmers now consider rodents (not insects, weeds or lack of soil fertility) to be the main factor limiting rice production.

5. Africa also suffers. In Tanzania, rats can eat more than 80% of the planted maize seeds in an area. During bad years, rats have wiped out hundreds of square kilometers of maize, the country's staple crop, destroying 50% of the crop or more. All the African countries suffer. It is the same everywhere, on all continents. Losses of stored rice and maize are reported to be even more severe in Latin America.

Black Rat

6. In Pakistan, rats consume several million tons of stored wheat grain annually; in Bangladesh losses of grain stored inside houses are estimated at US$620 million a year, in houses only. In India, rats outnumber humans ten-fold.


Of mice and men

Rodents are also known to be the carrier of plague-bearing fleas. Their urine and feces are linked to hantavirus outbreaks in the USA and in Thailand. "A number of rodents serve as reservoirs for human diseases, such as bubonic plague, tularemia, scrub typhus, and others. The plague that ravaged Europe during the mid-14th century was transmitted by fleas from rats to humans." (www.the-piedpiper.co.uk/th1.htm).

Buff-breasted rat (bamboo rat)

"Plague is still a problem throughout the world today, with annual outbreaks in parts of Africa that kill hundreds of people. Rats are closely associated with other diseases such as Leptospirosis and can rapidly spread other gastroenteric diseases such as cholera and salmonella. Recent research in Mozambique found that 18% of villagers tested positive for leptospira." (journeytoforever.org/at_rats.html)

"In parts of Africa up to 10% of people are regularly bitten by rats while they're asleep, leading to secondary infections and rat bite fevers from bacteria entering the wounds. And rats contaminate stored grains with their urine and feces, increasing the chance of disease." (journeytoforever.org/at_rats.html).

There are known techniques to reduce the various influences of rodents on human health. They should be strictly adhered to. There are also known techniques to reduce the amount of grain that is either eaten or contaminated by rodents. They should be made available and their implementation fostered. A grain of wheat saved is a grain of wheat earned: it is the same as if a newer higher yielding grain had been developed. The food security issue has to be attacked throughout the year, in the pre-harvest and in the post-harvest periods. Increased attention must be given to more effective techniques for grain storage, especially in rural areas. The Internet makes it possible for farmers around the globe to share their grain storage experiences, technology, and techniques.


Rodents and Food Security

Development of methodology for assessing the impact of rodents on rural household food security in Mozambique

This project will contribute to the purpose of developing and promoting effective and sustainable grain management systems. Specifically, the project will develop a methodology for assessing the impact of rodents on household food security, and their potential impact on health and nutrition of rural families. Control strategies will be based upon assessment and monitoring data for application on a village-wide basis.

Villages that have identified rodents as a serious constraint to their food security and/or health will be assessed and monitored for rodent activity. These assessments will be used to develop a rodent control programme on a village-wide basis that will aim to reduce the impact of rodents upon rural communities in consultation with the community. The assessment and monitoring strategy that is developed will be able to demonstrate that control strategies are having an impact upon the rodent population within the time-scale of the project.

             Source: http://www.nri.org/research/foodstorage-projects.htm



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