There was a programme on about them a couple of weeks ago.
There was one in Florida (i think) last year where it was inside a house and the bloke was asleep. The body has never been found. Scientists put a probe in to check its state and by the time they had done that and walked back to the measuring equipment, the probe had been sucked down a couple of feet.
Very scary. Also very weird how many are appearing. One in the Dales, one in the middle of the M2 in Kent, more to follow i should imagine.