Rat Attack

Rat Attack

PBS Airdate: February 24, 2009

NARRATOR: It is 1959: in this remote corner of India, freshly dug graves, too numerous to count, speak of an unfathomable horror. In the forests, men desperately search for food, as famine stalks the countryside. Mothers dig up roots to fill bellies. Some hike hundreds of miles to find rice for their starving children.

But it is the cause of this calamity that totally defies explanation. It is a natural disaster unlike any other, one that comes, not on the wind, like a cyclone or drought, but on four legs and by the millions. It is a plague of rats.

RICE FARMER 1: The rats just kept coming and coming, until they completely destroyed my entire rice field.

NARRATOR: Now, exactly 48 years later, an almost identical plague is sweeping the country again. Across the region, colossal armies of rats rampage through the countryside, obliterating rice crops, leaving nothing.

Local tradition says the rats pour out of the bamboo trees, that the forest gives rise to the plague. But what is the real cause?

Scientists know little more about this onslaught than they did almost half a century ago. That's about to change.

Biologists are racing to the scene of an event so steeped in myth, they don't know what they'll find.

KEN APLIN (Australian National Wildlife Collection): Rats everywhere, watching us.

NARRATOR: And they don't have much time to figure it out.

KEN APLIN: Everything we've seen suggests that come August, at harvest time, there's going to be huge numbers of rats in the forest and that their crops are going to be destroyed.

NARRATOR: Is there any way to avoid it?

It's a Rat Attack, right now, on this NOVA/National Geographic Special.

NARRATOR: On a September night, in the fields near a remote village in northeast India, the rice hangs ripe on the stem. Farmers, asleep in their bamboo huts, plan to begin the harvest in the morning. They've planted enough to survive and feed their children another year.

But under the cover of darkness, a force of nature is at work in their fields that will thwart all their plans. Like plagues of the past, this one is wrought by a creature called the black rat, one of the most common and most devastating pests known to man.

Over the course of three nights, as the villagers sleep, rats erupt out of the ground by the thousands, overrun the fields and eat everything in sight.

This year, there won't be a harvest.

KEN APLIN: James, we might have to spend the night here, I think.

JAMES LALSIAMLIANA (Biologist): I think so.

NARRATOR: Biologist Ken Aplin, a National Geographic grantee, has come here, all the way from Australia, to investigate, along with local biologist, James Lalsiamliana. They can hardly believe their eyes.

KEN APLIN: And I thought this field had been harvested, from a distance, but it's just been completely destroyed. It's not been harvested by people but by rats. And the corn is...also, it looks as though every corn is completely destroyed. No corn to re-sow and not even enough rice to re-sow.

I've never seen destruction on this scale in...anywhere that I've worked in Asia.

A very tragic tale, I think.

NARRATOR: The farmers expected to harvest 4,000 pounds of rice; they got 50. For the 40 families of the village of Thlangkang, it's going to be a desperate year.

They are not the only ones suffering. These catastrophic rat attacks seem to hit in a way that defies understanding.

KEN APLIN: I've heard about these things for, now for 10 years or more, all over Southeast Asia...desperately wanted to see it.

What exactly does happen? What is the connection of the rat outbreaks? No one knows. We've got no hard data, just myth and fiction. We need facts.

NARRATOR: Aplin's quest to figure it out how it happens began months ago when he first came to the northeastern Indian state called Mizoram.

It is a world apart, separated from the rest of India by Bangladesh. The people here are distinct, ethnically descended from the Chinese and religiously Christian, not Hindu as in most of India.

In the Mizo language, they even refer to India as the "mainland."

JAMES LALSIAMLIANA: Rats, they are coming from all over Mizoram.

KEN APLIN: All over the state?

JAMES LALSIAMLIANA: Yeah.

NARRATOR: Along with James Lalsiamliana, Aplin has been trying to track a wave of rat outbreaks as they sweep across the state. The scale of the onslaught appears to be astonishing. It's estimated that the rats have consumed over 50,000 metric tons of rice so far.

It would take a lot of rats to do that kind of damage. Aplin is about to get a hint of just how many.

KEN APLIN: And how many do we have here? What's this?

JAMES LALSIAMLIANA: Thirty thousand.

KEN APLIN: Thirty thousand tails? Thirty thousand tails?

NARRATOR: Ken's never seen, or smelled, data like this.

KEN APLIN: Tip them all out. Let's make a big heap.

Look at that. I've never seen such a sight!

JAMES LALSIAMLIANA: We'll start counting, one by one?

KEN APLIN: You can count them, and I'll start at the other end and identify them.

That's a fat one. What's that?

NARRATOR: As a way to fend off the tidal wave of rats, the government has offered a bounty of two rupees for every rat killed and its tail turned in.

KEN APLIN: These are almost all black rats.

NARRATOR: These 30,000 rat tails are just a fraction of the over one and a half million that have been collected. But so far, the government program has had little effect at stopping the wave of rats.

KEN APLIN: This is a great snapshot, James, of what breeds up—black rats, huge numbers of black rat.

NARRATOR: The black rat is a formidable foe and one of the most destructive species on Earth. Sneaking onto ships and carts, it spread from Southeast Asia around the world, carrying the plague to medieval Europe. They eat what people eat and can thrive in both cities and the countryside. They operate mostly at night, so they're nearly invisible. They are successful opportunists, omnivores who take advantage of any ready food source and then unleash their ultimate survival weapon:

more rats.

The pile of tails gives Aplin his first clue about which rat is the culprit here: this sample is more than 90 percent black rats.

KEN APLIN: They're not that common, normally, in these bamboo forests. Maybe they...under normal conditions, they might make up 10 percent of all of the rats in that community. So they've increased dramatically here, and the key is their more rapid breeding.

NARRATOR: Rapid breeding gives black rats a dramatic advantage over other rat species. Their gestation is 21 days, five days shorter than almost any other type of rodent. Pups also wean more quickly, in a little more than two weeks. In the right conditions, their numbers will shoot up exponentially.

The result is a plague of rats.

In the state archives, Ken and James have unearthed evidence that rat outbreaks have happened here on a weirdly predictable schedule: in 1959, in 1911, and, before that, in 1863. Documents dating back to the early days of the British Raj verify that every 48 years there's been a massive rat plague and famine.

JAMES LALSIAMLIANA: ...in December, 1911.

KEN APLIN: December, 1911.

Here, I received a helio from assistant superintendent...,

(a helio is when a, when one man stands on a mountain top with a mirror and flashes the sunlight in Morse code,) enquiring as to whether any damage had been done by rats in this sub-division as swarms were crossing the...

NARRATOR: The records also reveal that something else happens on the exact same schedule as these rat outbreaks.

KEN APLIN: ...forty-nine years ago.

Oh, look how it begins. When the bamboos in this district started flowering two years ago, the Mizos were dead sure that famine was at their doorstep.

They believe that the flowering of bamboos, which takes place once every 50 years, is the forerunner of rats' depredations on jhums, with tragic consequences.

NARRATOR: Mizoram is blanketed by 2,400 square miles of bamboo. Like wicked clockwork, every 48 years, it blossoms, fruits and dies.

In an uncanny quirk of nature, that's exactly when the black rats seem to come out. This great flowering appears to spread across Mizoram in a wave, taking about two years to complete.

The people call it "mautam," and it fills them with dread.

KEN APLIN: The nature of havoc caused by rats on jhums is simply devastating. Not a single stalk of paddy is spared.

If, for any reason, this paddy is lost, the people know no other way to go for their livelihood but just brood on their misery.

Very poetic as well.

NARRATOR: The last time it happened was 1959.

Then two years ago, right on schedule, mautam began again, slowly sweeping across Mizoram from east to west. The bamboo first bloomed along the Burmese border; a surge of rats followed a few months later.

The same thing happened last year in the middle and southern parts of the state. If the pattern holds, it's going to happen one more time, in the area around a village called Zamuang, and Ken is determined to be there to see and to document it.

KEN APLIN: mautam only happens once every 48 years. This is my last chance to work out what really happens during mautam, to get that connection between the bamboo flowering and the rat outbreaks.

NARRATOR: The size of the bamboo forests in Mizoram makes this bamboo flowering the largest in the world, but it occurs in other places in Southeast Asia and South America, also triggering rat outbreaks, famine and suffering.

KEN APLIN: And I think what we learn here can be applied and help millions and millions of people, worldwide.

NARRATOR: But first, Ken has to convince his colleagues it's real. Right now, many scientists dismiss it as folklore because it's only based on anecdote.

Aplin plans to quantify it for the first time, but he doesn't have much time to do it.

KEN APLIN: This is our last chance then, James, to see this in our lives, because by the time it happens again, I think we might have passed on.

JAMES LALSIAMLIANA: Yeah, 48 years.

NARRATOR: As Ken and James head for Zamuang, the village that hasn't been hit yet, they move through areas that suffered through mautam last year.

In Mizoram, the farmers practice slash-and-burn agriculture. They call it jhum. Once the bamboo veil over this field has been lifted, there are rat burrows everywhere.

KEN APLIN: Well, James, look at the number of burrows in this field. This pale soil dug up from below ground. Another one...

NARRATOR: It's evidence of how the rat onslaught unfolded here.

KEN APLIN: ...rat burrows going down here. There's a big one down this side. This one's got nest...old nest material in there; underneath the surface here, I think.

This field blows me away.

We've got a rat burrow on the surface, maybe one every yard, and that's what? Two, three thousand rats per acre?

And we add to that all rats that would have been living up in their leaf nests, up in the trees, in the bushes, in the bamboo, we may be looking at something like 10,000 rats per acre or more.

Now that's a number that is off the scale. I've never heard of that sort of rat density in forests, in rice fields, any kind of habitat anywhere in the world.

When was the main period of damage in the field?

NARRATOR: By interviewing the farmers who were hit last year, Ken is trying to establish a timeline, from when the bamboo fruit appeared to when the rats ravaged the fields.

It seems to take about six months until the rats attack.

KEN APLIN: February, March...rat population is visibly high in the forest by June.

NARRATOR: In normal times, the bamboo forest has very little food for rats to eat, so mother black rats reproduce infrequently. If food is especially short, they conveniently eat their young, further reducing the number of hungry mouths.

The bamboo fruit that appears every 48 years radically changes that equilibrium. Cannibalism disappears and rat reproduction kicks into overdrive. Over several months of bamboo fruiting, a single well-fed female can start a cycle resulting in nearly 200 offspring.

So take 50 females and they will produce a ravenous plague of over 10,000 rats. But it's only when the supply of fruit runs out that the rats, now in huge numbers, descend on the crops. At least that's Ken's theory. But he doesn't yet have proof.

Ken and James drive further west, determined to catch the mautam in action.

For sale, by the side of the road, they find a precious clue in the form of a tiny insect...

KEN APLIN: What is it, James?

NARRATOR: ...with an unflattering name.

JAMES LALSIAMLIANA: This is stink bug.

KEN APLIN: Stink bug?

JAMES LALSIAMLIANA: Yeah, stink bug.

KEN APLIN: They're still alive!

NARRATOR: According to local Mizos, these thangnang bugs only appear once every 48 years, just as mautam begins.

THANGNANG COLLECTOR: When there's no mautam, they don't come. We have no idea where they come from.

NARRATOR: Thangnang bugs are a type of aphid, but little is known about why they swarm during mautam.

What is known is you can eat them. The bugs are crushed into a paste and boiled to make a nutritious cooking oil.

This harbinger of famine is also a kind of manna from heaven.

After a day and a half of driving and looking for clues, Ken and James reach the village of Zamuang. It's bordered by a massive bamboo forest whose swaths of brown reveal that it's in full bloom, the first stage of mautam.

They have arranged to work together with a farmer named Moia, using his rice field as a kind of living laboratory.

Moia and his wife, Mami, are subsistence farmers. They live with their three children, working their small plot. Ken has seldom worked in fields where the stakes are so high.

MOIA (Rice Farmer): We are trying to have our own rice field. At the same time, we are very scared that the rats may eat up everything.

I think it's very frightening, this mautam.

MAMI (Rice Farmer):If the rats eat our rice, if they really eat it all up, it will break our hearts. One year's hard work will simply go all to waste.

NARRATOR: In the forest, at the base of Moia's field, Ken gets his first glimpse of what's to come.

KEN APLIN: Well, James, we're here: mautam.

JAMES LALSIAMLIANA: We're at the heart of the mautam.

KEN APLIN: An incredible amount of fruit.

JAMES LALSIAMLIANA: Yes, yes.

KEN APLIN: It's a perfect food for rats, James...

JAMES LALSIAMLIANA: Yes, yes.

KEN APLIN: ...the nutrition and the sheer quantity of it, vast quantity.

JAMES LALSIAMLIANA: Yeah.

NARRATOR: Ken is standing at ground zero, a place surrounded by trees laden with bamboo fruit. Over the next few months, he estimates that 10 tons of fruit per acre will ripen and drop.

The fuse has been lit.

NARRATOR: Though the bamboo fruit may trigger a plague of rats every 48 years, it also serves as seed for a new generation of bamboo, vital to life here.

Moia's neighbors use it to help him build a jhum hut, a kind of guard post in his field, so he can keep a careful lookout for rats right up to the harvest.

Without bamboo, life here would be remarkably different. Bamboo is woven into the very fabric of their days. Like an organic plastic, hundreds of items are made from bamboo, even food.

By weight, bamboo is 10 times stronger than steel, and a lot cheaper. It's even used as scaffolding in the construction of skyscrapers.

No other plant has the versatility of bamboo, though, surprisingly, its closest relative is your front lawn.

Bamboo is a grass, but there is nothing mundane about it. There are over 1,000 species, ranging from tiny ornamentals to 100-foot timber bamboo. In fact, it is a super-plant, an organism that has evolved an amazing array of adaptations. It can survive almost anything.

After the atomic explosions in Japan, bamboo was the first plant to reemerge. That's because nearly half the bamboo plant lives underground.

Moia's field is surrounded by thousands of bamboo stalks or poles, each of which is connected to the others by an elaborate underground stem structure called a "rhizome."

Rhizomes serve as the nutrient powerhouse for what is the fastest growing plant on Earth. In some species, rhizomes spread at a rate of a foot per month, frequently launching new poles above ground seeking light. In some instances, these poles can grow more than a meter in a 24-hour period.

I.V. RAMANUJA RAO (International Network for Bamboo and Rattan): So this was the original rhizome that came out and has formed the pole.

Now, what it has done now is to produce four rhizomes on one side and five rhizomes on the other, so you can see the multiplication ratio. For one pole you are having nine children, let us say.

Each of these would grow let's say, half a meter or a meter, and would again give rise to six, seven, eight, nine, ten new rhizomes.

NARRATOR: Ten rhizomes a year becomes 1,000 in three years and 10,000 in four.

This elaborate understructure acts as a natural retaining wall, keeping these wet, rugged hillsides from sliding into the Bay of Bengal. So for 47 years, bamboo literally holds this land and its people together. Then, in the 48th year, it turns on them.

The flowering and fruiting, and the rat onslaught it seems to trigger, may feel like a betrayal to the Mizos, but the mass fruiting is one of the bamboo's most astonishing survival strategies.

The bamboo common in Mizoram only lives for 48 years, but, before it dies, it pumps out so much seed, no predator, including the black rat, could possibly eat it all. That means at least some of the seed will survive to germinate and produce a new forest of bamboo.

No one understands the mechanism that allows all the bamboo plants to start flowering and fruiting at exactly the same time, but it seems to be driven by a remarkably accurate internal clock.

RAMANUJA RAO: The interesting thing is that if you were to take a part of one of these bamboos and you planted it far away, not connected with the parent plant, that would also flower. Even if you took it to, maybe, another continent, another country, it would still flower and die at the same time as the parent.

NARRATOR: Many species of bamboo share this internal clock, but the Melocanna bamboo, common in Mizoram, boasts one final asset for survival:

its fruit, with seed inside, is huge, 200-times larger than the average. This builtin food supply insures that the plant will survive.

Mass seeding events like these have had some unexpected benefits for species other than bamboo. For example, they may have led to the domestication of the chicken.

DANIEL JANZEN (University of Pennsylvania): If you look at chickens as a whole, they're just a pheasant.

And there are many, many species of pheasant in the Old World. One of them specialized on bamboo seeds, and that gave it a very different biology than all the other pheasant species have.

NARRATOR: Throughout Southeast Asia, wild chickens are called "bamboo fowl." And according to Janzen's theory, long before people began farming, these wild chickens learned to reproduce like crazy during mass seeding events.

That set the stage for domestication.

DANIEL JANZEN: And, of course, what happened was people then, sometime in the distant past, basically started feeding chickens scraps from the house, whatever it happens to be, and then the chickens turned on, at the house, like, sort of, a miniature bamboo seed crop. And suddenly you have a domestic animal who's just really doing the same thing that it always did in nature.

NARRATOR: But chickens and rats aren't the only species who eat bamboo seed. It holds a particular appeal for people.

In the capital of Mizoram, Thari, a police officer's wife, had the idea of using the fruit for pickles.

Knowing all the lore about the mautam—how rats eat the bamboo fruit and their populations explode—she holds a popular, but untested, view: that the fruit is an aphrodisiac.

THARI (Bamboo Pickle Maker): Ask my husband, he should know whether it works or not. Even our friends, after we ate the fruits, we told each other that it seemed to be very strong and really working.

NARRATOR: No one has ever studied if the fruit acts as a natural Viagra.

What is clear is that it is a tenacious survivor.

Even when the forest is burned down to the ground, the plant still produces fruit, popping the seed right out of the soil, ready to spawn new generations of bamboo and rats.

NARRATOR: With the chance to document the onslaught for the very first time...

KEN APLIN: Four different methods...

NARRATOR: ...Ken deploys some simple tools to do a census: a snare and a trap,...

KEN APLIN: Second method, also for catching rats.

NARRATOR: ...a candle, because rats nibble on wax like candy...

KEN APLIN: ...tie it on to a small tree, and the rats will come at night, and we'll be able to see that the rat has come to that place.

So we take the grease...

NARRATOR: ...and finally a tile, to measure the number of rats afoot in the forest.

KEN APLIN: And we can see their footprints, on here.

NARRATOR: He hopes these simple tools will give him some advance warning that the population is starting to explode.

In the meantime, Moia is scared. He knows what mautam has done in other villages as it has swept across Mizoram. He also knows what happened 48 years ago, during the last mautam, when famine engulfed Mizoram, reportedly killing thousands.

At the time, the Mizos, angry with the Indian government's response, rose up in armed rebellion, waging a 20-year guerilla insurgency. The rebels finally came to power and, today, along with aid organizations, they are providing desperately needed rice.

Still, in remote parts of the state, there are reports of widespread famine, though no one knows the true extent.

In the worst hit areas, child mortality is said to have increased threefold. The government and aid groups are trying to help by sending out desperately needed supplies of rice, but transportation is difficult, and it's hard to reach many of the villages that need it the most.

In the forests surrounding Zamuang, bamboo flowering and fruiting is in full swing. Ken is finding disturbing evidence that the rat population is on the rise.

KEN APLIN: ...bamboo fruit that's been taken in. There's one, one more...seven. The tunnels continue on.

This is just the chamber, in there, and the burrow goes off under the hill. But we've got seven, seven pups.

These are maybe just about a week old. But in only two weeks time, these animals will be big enough to leave the burrow and start fending for themselves. And about one month or maybe six weeks after that, the females among them will be sexually mature and able to start having a litter of their own.

NARRATOR: Based on early results from trapping and tracking, hundreds of female black rats are busily reproducing, confirming Ken's suspicions that a frenzy of hyper breeding is underway.

KEN APLIN: ...big, black rat.

NARRATOR: It's news that only a rat biologist would welcome.

KEN APLIN: A lot of people are disgusted by rats, but man, I love rats. I just can't get enough of them. They're kind of a speeded up version of a standard mammal, as though you've wound the clock up on them.

They run at an incredible pace. Their heart races along at about five, six times human rate.

I adore them. They're so successful.

NARRATOR: And they taste okay, too.

With a plague of rats on the horizon, there may be a certain satisfaction in eating them, as many Mizos do.

But Moia and his family fear it's the rats that will do the eating.

Right now, it's a race against time. Will the crops be ready before the rats are?

MOIA: This year, I've sowed the seeds, and I'm hoping for the best. I'm hoping the rats will have mercy on me. Then I will be able to harvest enough for my family, for the coming year.

KEN APLIN: I'm pretty concerned about the future of the people in this village. Everything we've seen suggests that come August, at harvest time, there's going to be huge numbers of rats in the forest and that their crops are going to be destroyed. It'll be a miracle if it doesn't happen, I think.

NARRATOR: In June, the monsoon comes. Three months of rain, in an otherwise dry climate, that nourishes the crops. Sometime in the next 12 to 14 weeks, Ken thinks that the black rats will finish eating the bamboo fruit and turn their attention to Moia's field.

After three months filled with rain, anxiety and dread, the villagers of Zamuang face a frightening future.

They hope they'll somehow escape the fate that has befallen so many others.

Ken and James return and immediately begin to look for signs of an impending attack.

KEN APLIN: I hope that we can get this harvested before the main rat attack comes on.

NARRATOR: With harvest about a month away, Ken is anxious to see who's winning the race between rats breeding in the forest and rice ripening in the field.

NARRATOR: Moia and the other villagers have been busy trapping and tracking...and the results are not what anyone wants to see.

KEN APLIN: We've got three months of trapping and tracking information from the forests and the fields. Through June and July, we got, pretty well, no footprint activity at all, consistently, night after night: nothing, nothing, nothing. Then we come through to the fourth of August and then, after that, consistently, we're getting footprints on multiple tiles.

And it's sustained. It's just, "bang," increase, and then it holds.

I'm just trying to work out what it means. All I can think is that the start of the breeding activity must have been incredibly synchronized. As soon as that bamboo fruit started to form, the females that were there in the population started to breed.

NARRATOR: Their pups weaned, mated and quickly produced a litter, but the original females didn't stop breeding. As their offspring were reproducing, they were at it again, multiple generations reproducing in synch, creating a multiplier effect.

It's worse than Ken expected.

KEN APLIN: I thought we'd probably see just a gradual increase in the population, but it looks like we're seeing these incredibly synchronized pulses of breeding activity and these young coming out in the population to run around on the tiles and to go into the traps.

NARRATOR: Ken estimates that six months ago, only about 100 black rats were living in the forest around Moia's field, but since then, massive quantities of bamboo fruit have fed three distinct birth pulses.

The first increased the population from 100 to about 600. A second pulse, in June, pushed the number up to 1,000 rats. Now, in early August, they are in a reproductive frenzy: almost quadrupling the horde to 4,000. A fourth pulse will create a ravenous army of close to 12,000 rats.

When that fourth pulse hits, the remaining fruit on the forest floor will have germinated and be inedible. Rice, in the field, will be the rats' only option.

But which will come first, the fourth pulse of rats or Moia's harvest?

KEN APLIN: Moia, just move around, so we can make a bigger circle. Watch out for the gully.

NARRATOR: To figure out where that fourth pulse is, Ken needs to find pregnant females.

KEN APLIN: All right, let's go.

NARRATOR: He stages a rat drive at the base of Moia's field to catch some.

KEN APLIN: There's one!

A great big pregnant female black rat, oh, full of babies, full of babies.

NARRATOR: Dissection reveals a breeding machine in overdrive.

KEN APLIN: These are the embryos and the placenta. She was already nursing a litter. Those young that she was nursing would have to be kicked out of the nest when this litter was born.

NARRATOR: There are usually a few weeks between litters; during mautam, there is no break at all.

This female was due in a week. Ken believes this litter could be the fourth pulse, the critical tipping point that would almost guarantee destruction of the crops in about one month's time.

And in a month, the heads of the rice will ripen from green to yellowish brown.

Moia is at his jhum field around the clock, watching his rice. It is almost ready.

Ken suspects that at the bottom of Moia's field, a fourth pulse of rats may be ready, too.

That night, Ken tries to determine how many rats are operating in this field.

KEN APLIN: Rats everywhere, watching us.

NARRATOR: In the dark, he faces an almost invisible enemy.

KEN APLIN: Listening out over the rice field, there's a whole mass of different sounds.

NARRATOR: He deploys an ultrasonic surveillance system to do a kind of audio census.

Black rats communicate through a series of high-frequency sounds.

KEN APLIN: And I'm hearing little clicking, random kind of clicking noises coming from up in these trees and nowhere else.

NARRATOR: The rats make this high-pitched click:

(Sound of rats)

KEN APLIN: And I suspect that's baby rats communicating with their mothers.

NARRATOR: Ken estimates that several thousand rats are spread between burrows and tree nests, chattering through the night.

It doesn't bode well for Moia's crop. Though it's not yet ripe, the rice at the bottom of the field has already been devastated. It's an ominous sign.

KEN APLIN: It's not surprising, given how many burrows we've got there, James.

The rice is just about all gone here. Look at all these cuts. They won't get any harvest, really, here...just completely trashed.

NARRATOR: Moia knows he's losing rice every night, but he thinks the crop needs one more day to ripen. It's a high-stakes bet, because his family's cupboard is almost bare.

MAMI: This is all the rice we have left. And I think it will only last for this week.

It's very important that we harvest whatever paddy we are growing.

KEN APLIN: Part of me, the scientist part, wants to see it. I've heard about these things for, now for 10 years or more, all over Southeast Asia. I've read about mautam. I want to see it. I want to see rats swarming through this field destroying it...desperately want to see it.

But, on the other hand, I've got to know Moia and his family and many of the other farmers in Zamuang, here, and the last thing I want is to see them lose their crop, because they're subsistence farmers. If they lose their crop, they're in for a really tough year.

NARRATOR: Moia has to make it through one more anxious night.

The gamble pays off. The next day, Moia and Mami finally harvest, with help from neighbors and from Ken.

KEN APLIN: It's really great to be seeing Moia and Mami here, harvesting their field and also to be able to help them in that process. It's quite a thrill.

NARRATOR: Although rats ate around a quarter of their crop, Moia and Mami believe they have enough to get through the next year.

They'll be okay, but according to everything Ken has learned, they dodged a bullet. The fourth pulse of rats should have hit here. What accident of timing saved Moia's field?

Ken has heard about another village that wasn't so lucky and sets out to see it. He knows this is the last chance in his life to solve this mystery.

KEN APLIN: ...there, James. We may have to spend the night here, I think.

JAMES LALSIAMLIANA: I think so.

NARRATOR: In the village of Thlangkang, the rats struck when the crops were still in the ground.

RICE FARMER 2: I went back to my field three days later, and all my rice was gone. And that's the way it was. The rats just destroyed the field.

NARRATOR: When Ken arrives in the village, he's searching for two things: proof of a fourth pulse of rats and details about when the mautam began here.

But first, he has to see what the rats did to the fields.

KEN APLIN: It's just been completely destroyed.

JAMES LALSIAMLIANA: See the grain scattered all over the place.

KEN APLIN: Yeah, everything destroyed.

Look at all the heads cut down here...all through the fields. Huge rat feast; nothing left for the people.

And the corn is also...it looks as though every corn is completely destroyed...never seen destruction on this scale anywhere in Asia.

Have you ever seen one, a hundred percent?

JAMES LALSIAMLIANA: No, no, no. This is my first.

KEN APLIN: Yeah. Very tragic tale, I think.

JAMES LALSIAMLIANA: ...from the corn.

KEN APLIN: No, it's been wrecked.

NARRATOR: Just as in Moia's field, there was a race between rats and rice, but here, somehow, the rats won.

To prove that a fourth pulse hit here, he has to find some rats, and that won't be hard.

KEN APLIN: This situation here is just on overload. There are just too many rats, not enough places to hide, and they're just all cramming in anywhere they can shelter. It's not really a sustainable situation at all.

This is the hallmark of a population in for a big crash.

NARRATOR: During the hunt, Ken bagged mostly young rats, a strong sign of a fourth pulse.

KEN APLIN: And that's exactly what we expect for that final phase of exponential growth of the population, where maybe 95 percent or more of the population is made up of juveniles—very, very young animals—and the adults are in the real minority. It's the young that are doing the damage to the fields.

NARRATOR: But dissection of one of the adult females they did catch delivers even more convincing proof that a fourth pulse caused the destruction.

KEN APLIN: If we have a look inside, we can read it like a medical record, if you know what you're looking for.

NARRATOR: Each embryo formed in a rat uterus leaves a scar.

KEN APLIN: Four from that side.

This grand old lady, I've just counted the incredible number of 42 little placental scars on her uterus. That's at least four litters. She's been pumping those out every month, month after month after month.

I think she was here right at the very beginning of mautam.

NARRATOR: Normally, a female black rat might produce only two litters in a lifetime. This one doubled that rate, effectively confirming a fourth pulse hit here.

So why didn't a fourth pulse hit when Moia's crop was still in the field?

KEN APLIN: When did the bamboo flower last year?

NARRATOR: In talking to the village head man, Ken finally finds the missing piece of the puzzle.

KEN APLIN: It seems that, although the flowering was about the same time here and Zamuang, the fruit production started about two months earlier here.

NARRATOR: The timing of the first fruit determines everything.

Here, fruit production started almost six weeks earlier, giving the black rats a fatal advantage.

KEN APLIN: That allowed the rats to start breeding earlier and for that final, massive fourth pulse to come erupting out of the ground.

A simple difference in the timing, huge difference in outcomes.

NARRATOR: mautam is a force of nature that can't be stopped, but, based on this research, it can be parried.

Ken's timeline reveals that approximately 30 weeks after the first fruit appears, a fourth pulse of rats will emerge. If there's a crop in the field, it's as good as gone.

But farmers can now plan with that deadline in mind, planting crops that mature sooner. And governments will be able to better predict where and when the rats will strike,

then plan their disaster relief accordingly.

Farmers in Zamuang reported the fourth pulse finally did arrive, 30 weeks after the first fruit appeared. But without rice to eat, an army of hungry rats simply starved in the forest.

The bamboo fruit now feeds a riot of growth, even as the plant's internal clock starts counting down again.

Moia and Mami's children and hundreds of thousands of others in Mizoram will be able to track it more closely next time.

They can't afford to forget. They have a date with the mautam, in 48 years.