Twice a century, India is attacked by huge rat armies that devour crops in massive destructive waves and leave people without any food. Scientists long dismissed it as an urban myth...until they discovered that it really happens, and why.


A massive bamboo forest covers about 26,000 square kilometers in a region encompassing northeastern India and parts of Bangladesh and Myanmar. For forty-nine out of every fifty years, bamboo is a godsend for farmers, who can use the plant as building material, clothing, and even food. But in the fiftieth year, the bamboo inadvertently creates a rat army of almost mythical proportions that wreaks havoc on the entire ecosystem.

Bamboo is a very aggressive plant, and it tends to muscle out any other surrounding plants. This creates a huge bamboo carpet throughout the forest. Bamboo has a life expectancy of about fifty years, and when the plant nears the end of its life cycle, it releases all its seeds in one fell swoop. The problem is that the bamboo that makes up the carpet is all on roughly the same schedule, meaning all the bamboo plants release their seeds more or less simultaneously once every fifty years.


Greenwich University Steve Belmain explains this process, and why it sets the stage for disaster:

"It's a way for the bamboo to ensure that the seeds survive. But when the bamboo seed falls - you end up with 80 tonnes of seed per hectare on the ground. That's 80 tonnes of food just lying there waiting to be eaten."

Local rats start eating that 160,000 pounds of bamboo seeds, which causes their population to skyrocket. Though the bamboo can provide a lot of sustenance for all these new rats, eventually they have to spread out and look for additional food sources to survive. Farmers' rice crops are perfect for the rats, but just about anything they can possibly eat gets eating by the rampaging rodent horde, turning the entire forest ecosystem on its head.

The current bamboo flowering started in 2004 and is expected to last into next year. This is the first time scientists have actually been on the scene to study the outbreak of these plagues of rats, which had previously been dismissed as folklore and myth. Complicating the matter was that, because of rural India's relatively shorter life expectancy, there were few living witnesses to the last attack fifty years ago. But now researchers know the truth, and they're certain the bamboo is the cause of it.


There are also concerns that global warming could make these rat armies even more destructive. Destructive cyclones become more common as climate change worses, and ecologist Grant Singleton explains how the recent cyclone Nargis helped make this current batch of rat armies even worse:

"Because the cyclone was so intense and so much life was lost, there were a lot of areas abandoned that would normally be cropped. And these areas became overgrown with grasses and weeds that were a major breeding ground for the rodents. Also smallholder farmers recovered from the cyclone at different stages, leading to the crops being planted at markedly different times. Therefore the rice crops matured at different times and provided food on the table of the rat for much longer than usual."


The good news is that the rat armies aren't invincible, and relatively straightforward pest control techniques like simple fences lined with rat traps could make a huge difference in keeping them under control. But farmers don't deal with this problem regularly enough to develop effective strategies to solve it, and the researchers have found a great deal of apathy and defeatism among farmers who routinely lose crops to the plague of pests.

Still, Dr. Belmain remains optimistic:

"They're either engrained in apathy because they've tried and failed to control it or they don't appreciate how much they're losing to rats. So you really have to hold their hands and show them their lives can be better. People can do a lot more if they're organised."


[BBC News]