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Comment by nazar | Hacker News Reader

They should import cats. Thats how they got rid from enormous rat population after Leningrad (current St.Petersburg, Russia) blockade during the WW2. That would be a natural way of annihilating rat population(passive killing).

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This reminds me of an old Simpsons episode:

----

KENT Our top story, the population of parasitic tree lizards has exploded, and local citizens couldn't be happier! It seems the rapacious reptiles have developed a taste for the common pigeon, also known as the 'feathered rat', or the 'gutter bird'. For the first time, citizens need not fear harassment by flocks of chattering disease-bags.

Later, Bart receives an award from Mayor Quimby outside the town hall. Several lizards slink past.

QUIMBY For decimating our pigeon population, and making Springfield a less oppressive place to while away our worthless lives, I present you with this scented candle.

Skinner talks to Lisa.

SKINNER Well, I was wrong. The lizards are a godsend.

LISA But isn't that a bit short-sighted? What happens when we're overrun by lizards?

SKINNER No problem. We simply unleash wave after wave of Chinese needle snakes. They'll wipe out the lizards.

LISA But aren't the snakes even worse?

SKINNER Yes, but we're prepared for that. We've lined up a fabulous type of gorilla that thrives on snake meat.

LISA But then we're stuck with gorillas!

SKINNER No, that's the beautiful part. When wintertime rolls around, the gorillas simply freeze to death.

Cats come with their own problems. They were introduced on Kerguelen Island to eradicate introduced rats. The rats are left, and the cats eat endangered bird eggs.

http://www.btinternet.com/~sa_sa/kerguelen/kerguelen_species...

http://en.wikipedia.org/wiki/Kerguelen

          'Look, I can explain,' he said.
          Lord Vetinari lifted an eyebrow with the care of one who, having found

a piece of caterpillar in his salad, raises the rest of the lettuce. 'Pray do,' he said, leaning back. 'We got a bit carried away,' said Moist. 'We were a bit too creative in our thinking. We encouraged mongooses to breed in the posting boxes to keep down the snakes...' Lord Vetinari said nothing. 'Er... which, admittedly, we introduced into the posting boxes to reduce the numbers of toads...' Lord Vetinari repeated himself. 'Er... which, it's true, staff put in the posting boxes to keep down the snails...' Lord Vetinari remained unvocal. 'Er... These, I must in fairness point out, got into the boxes of their own accord, in order to eat the glue on the stamps,' said Moist, aware that he was beginning to burble. 'Well, at least you were saved the trouble of having to introduce them yourselves,' said Lord Vetinari cheerfully. 'As you indicate, this may well have been a case where chilly logic should have been replaced by the common sense of, perhaps, the average chicken. But that is not the reason I asked you to come here today.'

--Terry Pratchett, _Making Money_

So long as there's something there to eat cats. Introducing one invasive species to cure another can lead to unpredictable ordeals.

There are always big predators at top of the biological food-energy chain. They are few in numbers. Anyways, I believe populations of cats and rats will fluctuate. Increase in cats will cause decrease in rats and then subsequent decrease in cats. Like phase difference between sine and cosine wave graphs.

I believe introducing some small wild cat population would be a right thing to do, tho I would like to hear opinions of experts.

Edit: I don't think cats are invasive in the way rats are

> There are always big predators at top of the biological food-energy chain.

Not on islands. That's why islands have such unique animals found nowhere else.

Wouldn't the cats eat the insects?

Not exactly their niche. They might hunt for insects, but it won't be enough in terms of energy acquired. So probably they will reduce in population until rats' population will restore back.

And its good to keep rats busy. They won't wander as freely as they do now and hence eat less insects.

Those particular insects look big and juicy though. I know for sure my cat would love a snack like that.

A reasonable model if you assumed that cats exclusively ate rats - and wouldn't wreak havoc on any other native rodent populations (if they still exist).

Don't cats eat insects, too? I'm all in favor of getting rid of the rats, but I don't think cats are a solution.

Trouble with cats is they often destroy bird populations as well, not sure how much of a problem this is in Australia, but in New Zealand feral cats are up there with pests that need to wiped off any island that is to be rehabilitated.

The Stephens Island Wren is an excellent example of this http://en.wikipedia.org/wiki/Stephens_Island_Wren

Feral cats are a massive problem in rural Australia. They decimate small native mammals. The idea of introducing them to control rats and save native animals is insane - the cats would wipe out everything smaller than them.

Introducing a foreign species into an ecosystem has failed spectacularly so many times I cannot believe people still propose it.

Unfortunately cats don't eat only rats, they also like birds for instance. Look at the dodo extension mentioned in another thread, domestic animals played an important role there. Then the birds usually keep (nasty) insects population in control, etc and keeping a balance is tricky.

Snakes or other crawling rat predators would probably be a better idea, but then trying to convince the island people to share their space with snakes and weird looking insects at the same time would probably not go well :)

Snakes have bad impact on birds as well. Maybe not adults, but the eggs. I believe there is always a bigger fish in the ocean, everything is just a matter of equilibrium and its rules of self-control. Humans and rats probably are the only species that ignore those rules.

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