I never knew how many legs an ant was suppose to have, so this is news to me. 
Robert: LOL 
I used to wonder the exact same thing. K9Girl pointed out the four-legged thing, and I actually had to look it up on the Internet whether they had four legs or six! Boy, was I dumb. xD
Welcome to Pixar Planet, Robert! 
i think its mainly because the extra legs would need movements, they cant just be all limp, and that would take a lot more time and money. the simplest of things can cost thousands of dollars.
I wouldn’t say that the simplest things cost thousands of pounds, as it is time and research that cost money.
But why do Tuck and Roll have extra limbs?
When I first noticed, I made up a crazy theory that the grasshoppers tortured the ants enough to make them lose some limbs.
Crazy idea, I know. But this shouldn’t be taken too seriously. 
Hey, that reminds me of a quote from Monsters, Inc: “Did you lose weight or a limb?”
Well, they’re woodlice, right? I thought woodlice were meant to have six or seven pairs of limbs, something like that. How many do Tuck and Roll have? I really can’t remember. 
I thought they were pill bugs.
EDIT: Thanks, LG! You’re so educated.
…Which are woodlice. 
As far as “realism” is concerned, the ants in ABL are less realistic than those of Antz. Number of legs and colour of “skin” are ok in the Dreamworks version.
But when you look at the panic crowd scenes in ABL, all the ants running when they’re scared by the grasshopers, you really have the feeling they are real. They move exactly like real frightened ants. Much more than the human-like military parades in Antz.
I definitely prefer the Pixarian “realism”.
Antz has a more real “look”
ABL has more real…um, reactions/emotions.
I don’t think the Lighting and shading in Antz was nearly as good as that in A Bu’s Life. Also even though the Ants in Antz where more realistic looking, the characters in A Bug’s Life feel much more alive.
I guess they were more realistic looking becuase the actual color? The ants in Antz were redish. But you get blue, purple, and pink ants for ABL.
Well, you have to admit that real ants are
[size=167]ugly[/size]
Well, I’m not going to say that. BUt I will admit the bugs from ABL are more beautiful and better looking
Oh, yes, much!
Oh, and I believe the bugs in ABL are more funnier than the ones in Antz.
Here’s what i think, you can definitely relate more to the Ants in A Bug’s Life, they are beautiful designs, and have great color choices, not to mention the variation in legs, to differntiate the more beastly bugs from the more human ones. The “realism” in Antz is just, disgusting. I really can’t stand the ants in Antz, and the ants/bugs in A Bug’s Life move more realistically, and don’t look like androids. Last but not least, A Bug’s Life is way more enjoyable to watch.
The two legged ant just looks better, and makes it easier for audience members to identify with them because they look more human and less alien, even though ants do have a total of 6 limbs in reality.
Another reason for giving the ants 4 limbs besides time and money, as stated above, could be technical difficulties. I recall reading somewhere that the most amount of ants they were able to fit in one shot was 800. Now, that’s all ready a lot of models, which means a LOT of polygons, and thus more rendering time. Add on two extra limbs for each ant, and that’s even MORE polygons and even LONGER rendering time. Sometimes computers crash when they’re processing to much information. I watched a video on the Cars website where they had that problem durng rendering time for Cars.
Either way, the ants in ABL are just cuter and better looking all around in every single way than the characters in Antz.
What’s so realistic about ants standing on two feet? Even with the added limbs, Dreamworks phailed.
Exactly what In was thinking . I was wondering the same thing a little while ago. But, yeah, it was probably to make them more human like so as to make them easy to relate to. Also, they probably kept the six legs on the grasshoppers to make them less human and more evil.