I don't know where she learned this, but our daughter steps on ants if she sees them?! The only explanation I can come up with is that she used to love to play Bugs and Buttons:

http://www.littlebitstudio.com/bugsandbuttons.html

Or maybe kids just love to step on ants... I remember sending some ants to Valhalla when I was a kid.

Does your LO like to step on ants?