Forum Moderators: open
A search on "Deep Crawl" on this site will tell you a lot about it, as well as "FreshBot" or "everflux"
In a few words, the so-called "Deep Crawlers" are the robots doing the full indexing of your site. You may find those in your log files as their IPs are always starting with 216.238 This happens monthly and last for a few days. We are all waiting for them to show up really soon now ;)
The fresh crawlers are the robots visiting some sites at regular intervals, sometimes many times a day, that will update the index with "fresh entries".
Their IP always start with 64.68...
Dan
<edit>corrected typo</edit>