Which ant species is characterized by smooth grooves on its head and thorax?

The Pavement ant is distinguished by the presence of smooth grooves on its head and thorax, which is a key identification feature. These grooves give the Pavement ant a unique texture and appearance that can help in differentiating it from other ant species. Typically, this species has a brown to black coloration and is often found in urban areas, contributing to its commonality and recognition.

The other ant species in the choices have distinct characteristics that set them apart. Fire ants are known for their aggressive behavior and reddish coloration, while Carpenter ants are recognized for their ability to excavate wood and have a more robust body structure. Leafcutter ants display a unique appearance due to their leaf-cutting behaviors and usually have large mandibles. Hence, the specific grooves on the head and thorax are a defining trait of the Pavement ant, making it the correct answer.