A Steel Spider is a construct used by an inventive Magic-user to guard their possessions. It is made of steel with jeweled eyes (worth 100 gp each if removed). Its main body is one foot in diameter, with each leg two feet long. It is often painted black to blend in with its surroundings. It has Darkvision out to 120 feet.

A steel spider is often placed in ambush, and can only be detected on a 1 on 1d6 if it is hidden (even with Darkvision). It can leap 30 feet, and automatically gain surprise when making a leap attack if it has not already been detected. It attacks with sword-like forelegs.