The Shalka are underground dwellers who need volcanic gases to live and can easily survive immersed in lava. They use sound waves to navigate (as their eyes are practically useless), as well as to stun and hypnotize their prey. They are described as "bioplasmic" creatures; therefore slaying or blasting their bodies doesn't kill them, and they are also capable of fusing their bodies together to form a new gestalt organism. Their bodies are generally worm-like, but can vary in size and form according to the individual's function within the hive: from the massive semi-humanoid Shalka Prime which leads them, to minuscule parasitic Shalka which can be implanted in humanoid hosts.