Are ants two-dimensional animals?

No, they are not.. Just because they are constrained to move in 2D surfaces always doesn't make them 2 dimensional. You should not ignore their height , however small it might me, its still measurable, thus giving it the 3rd dimension. However such fancy words are seldom being used to describe Riemannian Geometry. read more

As small as they are, ants, like every single object in our 3D world, have dimensions of width (distance between opposite legs), length (distance from the ant’s head to the ant’s back), and height (distance from the ground to the highest point of the ant). read more

I seem to recall reading somewhere that very small creatures such as insects in general experience a two-dimensional world; they don't "see" a third dimension because they're too small for it, or something along those lines. read more