Canoptek Spyder
Canoptek Spyders (formerly known as Tomb Spyders) are Necron constructs used to watch over and tend the sleeping Necron Tomb Worlds like a glorified house maid. These Spyders despite being glorified house maids are pretty formidable defenders and are great at driving those pesky kids off their masters lawn yard.
Overview
Canoptek Spyders are by function, the Necron's Enginseer, in which they are often low level engineers who look after the sleeping Crons against decay and external threats. They are often armed with hives of Scarabs (Usually housed inside the Spyder's back) in addition to self-repair backup systems. They are also capable of directing Wraiths against any who are brave/stupid enough to venture into a Necron Tomb.
Whilst Canoptek Spyders are not sentient by any strict definition, their complex and layered sub-routines are incredibly resilient and can adapt to most situations like that of an animal. If a triad of Canoptek Spyders are operating in concert, one takes overall command, harnessing the processing capacity of the others to create a gestalt artificial intelligence far greater than the sum of its parts. This hyper-efficiency is passed onto all Canoptek Wraiths and Canoptek Scarabs in the immediate vicinity, allowing the Canoptek Spyders to lead an extremely well-coordinated and precise response to any threat, be it a failed stasis-matrix or an enemy incursion.
However the most dreaded annoying aspect of Tomb Spyders is their ability to quickly repair other Necron Warriors on the field of battle. This means that if your Necron lord for some reason, doesn't have the re-animation protocol, then you can use the Spyders as a back up just in case. Spyders also possess the ability to rapidly manufacture swarms of diminutive drone-like constructs in vast, shimmering clouds if they want to annoy the enemy.
While Canoptek and Tomb Spyders are different varieties of the same construct. Let's not kid ourselves when we know that the Canoptek is a revamped Tomb Spyder and that Games Workshop is too lazy to be bothered to make two different rules for two types of Spyders.