Why ants are small?

Tom, I got a couple of my engineering buddies to read Michaels book,one of their first comments 'ants as big as cows couldn't move'. I have no background in this area and wonder if you could comment?

Chuck F

Ants are the strongest creatures known to man. They can lift items 1000 times heavier than their body weight. Their muscles are hundreds of times more efficient than the best electric motor that exists on Earth.

Experts in biology say that the main thing that limits the size of ants is the lack of lungs. Ants don't have lungs.

Tom