Dub a pronounced, round rear bump for the abdomen. Use enough dubbing to create a clearly ball-shaped profile. This is one of the few patterns where you actually want a plump dubbing ball rather than a smooth taper.
Advance thread forward to midshank, leaving a visible gap. The bare shank in between represents the ant's narrow waist.
Wrap 2-3 turns of hackle in the gap. The hackle supports the fly on the surface and suggests the ant's legs.
Dub a slightly smaller front bump for the head, about 2/3 the rear bump size.
Whip finish. The whole fly should show two clear bumps separated by hackle.