Scarab
Scarabs (Scarabaeus sacer) are a species of Dung Beetles native to the Mediterranean region. Said beetles are notable for making spherical masses of dung which they lay their eggs in and roll into protected burrows as well as having significance in ancient Egyptian mythology.
Necron Scarabs
Necron Scarabs AKA Canoptek Scarabs are beetle like robots about 30cm long capable of limited flight and able to disassemble and reassemble matter at a molecular level. Scarabs have a variety of functions, ranging from maintenance of Necron bases and machinery to combat. While an individual scarab can be put down with a good lasgun shot, they generally travel in groups. A swarm of Scarabs can eat a Leman Russ Battle Tank and its crew and crap out a pile of slightly damp metallic dust with some carbon and calcium impurities in seconds. Give them some more time and they can also crap out the tank's mass in new Scarabs. Scarabs are not sapient, they are generally slaved to either Necron overseers or Spyders. If neither is present, Scarabs tend to become mindless von Neumann Machines eating everything and making more Scarabs until you have a planet with its entire surface covered with the little bastards.
Flensing Scarabs
Flensing Scarabs are a special type of Scarab meant to strip flesh from bone. They are much smaller than the common garden variety, being the size of a beetle. However their small size doesn't stop them from OMNOMNOMing your largest Tyranid or Squiggoth in mere minutes.
Mindshackle Scarab
Mindshackle Scarabs are a even more specialized type of Scarab. As their name implies, they are very small Scarabs used to burrow into the victim's skull and ASSUMING DIRECT CONTROL on the poor sod, turning them into a mindless slave to the 'crons.
Oldcron Scarab
The initial tomb awakenings produced larger, more specialized Scarabs. These creatures were little more than bombs with legs that crawled over the target, seeking weak spots to exploit. Against infantry, this typically involved clamping onto the target's face before exploding their head in a shower of gore.