Nobody knows where they came from ... or even exactly what they are.

But, like the plot of a low-budget horror film, trillions of tiny 'crazy' ants are invading Texas.

They have a liking for computers, other electronics and most of the modern machinery that makes the world go round.

Not because they see them, or the associated wiring, as food. In a phenomenon baffling scientists, they simply seem to be attracted to the heat, magnetic fields or the hum and vibrations from machines.

But they then go on to destroy them by sheer weight of numbers, shorting out electrical circuits, clogging filters and pipes and bringing moving parts grinding to a halt.

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Fire alarms have been set off by them, domestic gas meters have seized up and pumping stations at sewage works put out of action.

Even Nasa is worried as the unstoppable reddish-brown ants less than an eighth of an inch long head for the Houston space centre. The Russians were so concerned they telephoned to make sure that the orbiting International Space Station is safe.

The insects have been called 'crazy' because, unlike other ants which move purposefully in single file, they swarm in random directions.

Tom Rasberry, a pest exterminator, first came across a few hundred of the ants in 2002. There are now millions of colonies, spreading out at about half a mile a year.

Full article here.