The number of googles spiders

The number of googles spiders what does it stands for

[Ove]

On my site i have a lot of the google spiders but mostley there is just these numbers of them is there any more of them. How does that works with the diffrent numbers of the spiders, Are they doing diffrent things.

crawler11.googlebot.com
crawler10.googlebot.com
crawler12.googlebot.com

/Ove

[SmallTime]

I suspect that they each have an assigned neighborhood, but once they get excited about following links they stray out of it, and start running into each other. Perhaps they are teams of Googlers racing. It seems at least, that they come in via different pages.