Ok folks - I have same problem on one of my sites. I have been trying to track this thing down for about a week.
Here's what I am currently trying. Since this thing does execute java - I downloaded and installed the AXS tracking script from Matt's.
I have four webpages getting pounded by this thing and I'm tracking all the data that AXS gives for these webpages. I'll be looking for a pattern.
Also, I setup an ip ban script not identified within the robots.txt and htaccessed out all know good robots. I'll see what I catch.
I'll share what I learn