Psychopathically violent and religiously fanatical spider-like aliens. They worship their twin dark gods, Dogar and Kazon, who supposedly speak through the HyperWave Channel 44, which coincidentally is the channel the Umgah love to send their prank messages on, one of these which almost led to the extinction of the Pkunk.
Humans have many horror stories of the Ilwrath and the sick things they do to their prisoners of war. After the war Ilwrath planned to sacrifice Human beings to their dark gods in a bloody ceremony, but were fortunately forced to back off by the Ur-quan Kzer-Za.
In the end of SC2, the Ilwrath met their doom fighting the Thraddash in a war which led to both race´s annihilation. Good Riddance.