Spider Bombs are rarely encountered in-game, but they are very dangerous. These are tripiod suicide robots and will explode once they are close to the player. Spider bombs are mostly found in the underground areas such like sewers or abandoned places, where they are the most likely to seek out and eliminate any hiding Red Faction fighter. They are usually found in packs, and once they spot the player they will start charging at him/her. When they get close, they jump on the player and explode. Spider Bombs deal fairly high damage and they can kill the player rather quickly, so do not underestimate them. Because they are weak, but come in large numbers, the rapid-fire weapons are the best answer to them. In particular, the Slienced SMG works the best. Other good options are the Shotgun or the Machine Pistol(s), If grenade launcher running out of ammunition.
Spider Bombs are first encountered in the underground chapter, mainly in the abandoned subway station. Later they will resurface in the Hanging in the Hood chapter and the Nano Labs inside Sopot's Statue.