Subject: Why do spiders have varied leg lengths

I am seeking to take biological inspiration to construct legged robots.  One of 
the questions that bugs (excuse the pun) me is why spiders have different leg 
lengths with respect to body size.  Different leg lengths will result in varied 
abilities to traverse uneven terrain, and yet the spiders live in very similar 
environments.  You would expect an evolved fixed ratio between the body size 
and leg length?.  On a more technical level, does a spider use its legs 
to 'prod' and touch its environment to form a mental map of its surroundings 
without vision? - Thanks     

Re: Why do spiders have varied leg lengths