I made some changes to my crawlers. They still follow the same 6 rules as before, but I changed it so now turning and backtracking along a path no longer take up the crawlers "step", so now they all find alternate paths much faster. This was a design choice the first time, but I like it more now.
I also got rid of the hard coded step distance, so now crawlers can move any number of spaces in a step instead of just 2. I used 2 so the paths are spaced apart, but there is no reason they have to be. So now I could do a very inefficient flood fill with crawlers.
Crawlers can now change the color of the trails they leave behind.
The mouse can now spawn crawlers too. Which lets you do cool stuff.
You can play with Crawlers yourself here.