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 are pretty formidable defenders and are great at driving those pesky kids off their masters lawn.
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 nominally different varieties of the same construct, let's not kid ourselves here. We know that the Canoptek is a revamped Tomb Spyder.
Hard Crunch
As of 9th Edition, Canoptek Spyders have pretty much the same grab bag of diverse tricks as ever, with finally a good enough base statline to be worth putting in a list. In the transition from 8th, Spyders gained a whole two wounds, one attack and a good buff to both their weapons and abilities.
The baseline Spyder does lack most of these options : the two that you get for free are Scarab Hive, a neat if list-dependant ability to reanimate a Scarab for one unit within 6" as well as, oh yeah, 5x S8 AP-3 damage 2 attacks, allowing even the most barebones 60pt Spyder to maul both vehicles and elite infantry.
Everything beyond that costs extra points, but is mostly worth shilling for. Its ranged weapon, the Particle Peashooter peppers the enemy with blunt dice, having lost one strength since 8th and still having no AP. On the upside, the Spyder mounts two of them and they are each Assault 6 (doubled !), meaning 3 Spyders will make you throw an overwhelming 36 shots. With that volume of fire, raw statistics dictate that you're bound to make one of them stick at the enemy. And your opponent will likely try to remove them just so you stop having to borrow his dice with your greasy hands.
The next most useful tool is the 5pt Gloom Prism, a welcome psychic deny (something Necrons often struggle to find). It didn't use to mean much for the Spyder considering it was largely trash but it is now a welcome addition.
Finally and most situationally, Fabrication Claw Arrays provide the Spyder the ability to repair Vehicles within 3", D3 wounds at a time. Of debatable use - if your list contains a decent number of them it could come in handy, but do make that calculation ahead of time.
The absolute least you can do for your Spyders is give them a Technomancer that can enchance their rolls and maybe throw them buffs. The Spyder naturally feels most at home in a Canoptek-themed list where it can provide support to screening Scarab swarms and shower the mid-field with particles, but it can be worth considering if you take Arks of any kind, Triarch Stalker or for that matter the Silent King.