The Sentarii looked like large soldier ants, towering over humans. They had shiny black carapaces, narrow heads, glowing black eyes, powerful mandibles and sharp claws. Though peaceful by nature, they could fight and were capable of killing a Sontaran with their bare hands. (PROSE: Shakedown)
The Sentarii were the leaders of the inhabitants of Sentarion; even the Harrubtii would obey them to a degree. They worked in the universities and temples. They were the only ones allowed to read the sacred texts of the Shining Ones. (PROSE: Shakedown)
The Sentarii evolved from soldier ants and were the dominant species on Sentarion. They would war endlessly with each other, until the Rutan Host arrived on the planet. The Sentarii were modified by the Rutans, becoming the peaceful caretakers of the wormhole above Sentarion.
At some point in the 26th century, Bernice Summerfield came to Sentarion, looking for information on the Rutans. The Lord Chancellor of the University, a Sentarii, agreed to let her research on the basis of his friendship with the Seventh Doctor. When she was caught trespassing in the sacred Temple of the Shining Ones, he was able to save her from the Harrubtii, though she would be unable to leave the temple. He later witnessed the arrival of Karne and was killed while defending him from the Sontarans. (PROSE: Shakedown)