Random movement with rotate

If you look at this site and enter site. You will see 2 litle things moving on you screen.
I need somthing like this aswell only then for like 50 bugs. I found lots of ways to make this with rondom movement scripts but i also need it to turn. So when its going to the bottom its pointing to the bottom and when its going up its turns pointing up.
Does anybody know a good tutorial for this or a tip or maybe even a source file ?

thanks in advance