Grub

Grubs or “worms” are common alien Annelids encountered aboard the Von Braun and UNN Rickenbacker in System Shock 2.

Overview
Grubs are among the simplest annelid life forms bred by the Many. They are small, wormlike creatures that crawl along the ground, pursuing any humans they can detect. Forming the first stage of the Annelid life cycle, Grubs are biologically female. They lack a digestive tract, relying on an energy reserve stored during their incubation inside the Grub Eggs. When this reserve is depleted, the creature enters a dormant state until a psionic trigger revives it.

Grubs are parasites, latching onto a human host and burrowing into them, hijacking the host’s nervous system. Via psychic telepathy, the worms connect the victim’s mind to the Many’s consciousness, which overpowers the victim’s reasoning and will. This process transforms the host and Grub collectively into a Hybrid. Grubs are not capable of turning the player into a Hybrid. However, they will still attack the player on sight by leaping at them, dealing a small amount of damage. They are also difficult to strike with the Wrench due to their small size, though they die in a single hit.

Grubs can be identified by the distinct chittering sound they make upon hatching or sighting the player.

Strategy
Annelid Grubs are a very common sight aboard the Von Braun and the UNN Rickenbacker. They appear as early as the Engineering Deck, and will be seen intermittently for the rest of the game. As large worms, they're incapable of doing serious harm to the soldier, and are at worst an annoyance. All weapons, except for the Laser Pistol, can kill a Grub in one hit.

Later in the game, they will tend to appear in greater numbers, often feasting upon human corpses. In large numbers they become significantly more difficult to deal with, as they're capable of leaping at and swarming the player. Do not bother wasting ammo on the Grubs unless you need an explosive blast to kill a large number of them in a hurry; instead, use melee weapons to dispose of them one-by-one. While it is possible to 'swat' a Grub flying toward you in midair, doing so is very difficult and it will likely hit you for minor damage. Wait until they're on the ground, then deal with them appropriately.

Some eggs are hidden in difficult-to-see spots on the ceiling, so watch out for Grubs falling from above!

Trivia

 * A large portion of the worm is still seen on the Hybrid when attached to it.