True. But I have seen cooperative ant efforts take a whole cheese doodle away without biting it off in pieces. Some of the lazy ones rode on top.
Naw, the ones on top are there for counter balance and navigation.
Mmmm…can ants be trained and harnessed the way fleas can in a flea circus?
Oh, and welcome to the SDMB, sealerdave. Enjoy your stay here and remember that play is one of the most fun, and therefore effective, ways to train mental skills.
You’re in mangement aren’t you? 
“Alright guys, get ready; on the count of three…”
True, but if we’re assuming that all ants can carry a set fraction of their body weight,[sup]1[/sup] then the extra space taken up by the larger ants will be more than compensated by the extra weight they can carry. If the length scale of a single ant is L, the number of ants you’ll be able to fit under the slab is proportional to 1/L[sup]2[/sup], while the amount of weight they’ll be able to lift would be proportional to their weight, which would be proportional to L[sup]3[/sup]. So overall, the total weight liftable by ants which can fit under a given surface area would be proportional to their size.
[sup]1[/sup] Of course, biomechanics probably doesn’t allow for this assumption, so who knows?
Clearly the solution is to just find one 15 lb ant! 
Where is E.O. Wilson when you need him?
I for one welcome our 15 lb. human moving ant overlords
well, someone had to post it
My thought was the same as Burrido’s. After watching The Naked Jungle, I’d bet ants could cart off a person piecemeal, if theyu wanted.
My next thought was the Gary Larson cartoon that shows the ants carrying a baby with a big stupid grin on its faxce. The lead ant yells “You idiots! We’ll never get that thing down the hole!”
Okay, first we need a handling mechanism, because humans are too soft to pick up this way. You get the same problem when you try to squash ants on open ground. If you don’t have hard shoes, you just piss the ants off, with a very low kill ratio.
So, we put on some light metal or plastic pads on the downward side of the human to be moved. We engineer grooves, and indentations throughout the pads. That allows the ants to get under the human and in position to do some serious lifting. If we do this right, we can increase the number of ants up to a significant fraction of the total number that can fit in the shadow of a supine human form. Since we don’t want the articulation of the limbs to defeat our total lift, I suggest a carefully shaped single sheet of magnesium alloy, thin, but curved for strength, and conformation to the shape of the body. We choose a human of less than average weight by the amount of the weight of the platform.
Now we got possibilities.
Tris
And harnesses - tiny little ant harnesses - yeah, that’s the ticket!
What if they have a pointed stick?
How many ants would it take to carry a coconut?
Are they allowed to tie it between them?
Naw, just get yourself one of these!
Once, when I was about 10 years old, I found a mass of ants gathered at the edge of the sidewalk. The group was roughly 8 inches across, and apparently several ants deep. Maybe they were:
performing cheerleader routines,
singing “The Messiah”,
tramping down the underprivileged,
having a soccer riot,
giving a shiatsu massage to the bottom layer,
improvising a musical version of “Yertle The Turtle”,
eating a Moon Pie,
amassing a large enough group to kick my ass,
signing a petition to protest the cruelty of human children,
trying to stomp a hole in the sidewalk,
waiting for an aardvark, forgetting that aardvarks don’t live around here,
having misspelled themselves, were seeking uncles,
looking for work as antacids, or…
Oh, dude! I got a little too involved in that.
Anyway, I saw it as an opportunity to vanquish a horde of ants. Hahahahahahaha! It didn’t work, though. I stomped as hard as I could, and when I lifted my foot, there was not a foot-shaped group of flat ants. There was still a thriving, wiggling political metaphor, seemingly unharmed. It taught me a valuable lesson about the limits of what one man can do (No, strike that, I just thought it was strange. It didn’t teach me a damned thing.)
In other words, multiple layers of ants were impervious to my mighty foot. Why? I dunno. What do you take me for, a fizzy cyst?
No, that won’t work–Union Regulations and all. Fascist ants might be able to work in such close quarters, but it would be totally inhumane.
I hear that a single ant can move a rubber tree plant.
You don’t want to mess with the Intenational Brotherhhod of Formacids. They’ll rip you up into little pieces.
The question as yet unanswered here is, if every ant in the Southern Hemisphere jumped up in the air at the same time…