throttling bandwidth

[Insurance Squared Inc.]

My ISP called and said my nutch crawler is chewing up 20mbits on a line 
he's only supposed to be using 10.   Is there an easy way to tinker with 
how much bandwidth we're using at once?  I know we can change the number 
of open threads the crawler has, but it seems to me this won't make a 
huge difference.  If I chop the number of open threads in half, it'll 
just download half the pages, twice as fast?  I stand to be corrected on 
this.

Any other thoughts? doesn't have to be correct or elegant as long as it 
works. 

Failing a reasonable solution in nutch, is there some sort of linux 
level tool that will easily allow me to throttle how much bandwidth the 
crawl is using at once?

Thanks.