Dementor question

[Eric Oppen]

No: HPFGUIDX 55378

How fast can a Dementor travel?  Or are there other Dementors than the ones
at Azkaban (and Hogwarts during PoA)?

Reason I ask is this:  When Cornelius Fudge came to Hogwarts to watch the
Third Task, I "hae me doots" that he brought along a Dementor---"no, you can
_not_ come watch the Triwizard Tournament's Third Task.  _And 'Bambi eyes'
won't help!_"  If only because of the creatures' reputation and effect on
others, I think they're probably not welcome most places.

So when "Moody" turned out to be Barty Crouch, Jr., which apparently
surprised even Professor Dumbledore, he'd have had to get one _fast_ to have
one ready to roll when he was called into the castle.

Can Dementors apparate?  Can they, if they can apparate, apparate onto the
Hogwarts grounds?  We know that _wizards and witches_ can't do this, at
least according to _Hogwarts: A History,_ but we've seen (in CoS) that
house-elves apparently can do something of the sort.

If Dementors can apparate, what's to prevent them apparating off Azkaban
Island every so often for a yummy snack on the mainland?

--peering around uneasily for Dementors,

Eric