Depends on the bot in question.
Some like Google and Yahoo you can actually limit how often they visit your
website hosting. I know Google can be done through the webmaster tools, not sure on Yahoo but I am sure it was mentioned in the blog link above.
You can also limit where the bot can access using robots.txt if you don't want it to index a particular portion of your
website hosting. Or you can use robots.txt to create a sitemap if you find it's not index particular parts of your
website hosting. I have used the latter method and it has improved the pages indexed on the search engines, especially dynamic content from my CMS.
Google robots.txt there are a loads of
website hostings regarding it's use and if you have a google account they give you ways to test your file live.
Tim