Red imported fire ant workers range in size from small to medium, making them polymorphic. Workers measure between . The head measures and is wide. In the larger workers (as in the major workers), their heads measure and wide. The antenna scapes measure and the thoracic length is . The head becomes wider behind the eyes with rounded occipital lobes present, and unlike the similar-looking "S. richteri", the lobes peak further than the midline, but the occipital excision is not as crease-like. The scapes in major workers do not extend beyond occipital peak by one or two scape diameters; this feature is more noticeable in "S. richteri". In medium-sized workers, the scapes reach the occipital peaks and exceed the rear border in the smallest workers. In small and medium workers, the head tends to have more elliptical sides. The head of small workers is wider out front than it is behind. In the major workers, the pronotum does not have any angular shoulders, nor does it have any sunken posteromedian area. The promesonotum is convex and the propodeum base is rounded and also convex. The base and declivity are of equal length. The suture of the promesonotum is either strong or weak in larger workers. The petiole has a thick and blunt scale; if observed from behind, it is not as rounded above in contrast to "S. richteri", and sometimes it may be subtruncate. The postpetiole is large and broad, and in the larger workers, it is broader than its length. The postpetiole tends to be less broad in front and broader behind. On the rear side of the dorsal surface, a transverse impression is present. In "S. richteri", this feature is also present but much weaker.