Cybermats are minor antagonists that resemble bugs and are servants to the Cybermen in Doctor Who.
Tomb of the Cybermen
In their first appearance the Cybermats they were in the tombs of the Cybermen, lying dormant like there masters. A smaller one was found by Victoria (the doctors companion). When they Cybermen were reawoken, this one did to. It attacked Katriana who was holding Victoria at gunpoint, accidentally saving her, Victoria destroyed it with Katrina's own gun. Full sized one's were used by the Cyber Controller to attack the humans, after he and the other cybermen were trapped underground by the doctor. They attacked by homing on brain waves. The doctor was able to disable them with an electic cable.
The Wheel in Space
The Cybermats (with a slightly different look) were used for sabotage on a space station, draing the power. These ones were also armed with special lazer guns in there eyes, which caused a painful stinging sensation when fired, and enough of them could kill. As was the fate of a poor engineer who found them. The Second Doctor defeated them by jamming their audio frequency causing them to disintegrate.
Revenge of the Cybermen
Now looking like snakes, these Cybermats were remotely controlled by the Cybermen. They inject poison into their victims with fangs, and have no eyes. Like there masters they are defeated by gold dust, meaning that they share the Cybermen's weakness. The doctor later remodified one full of gold dust, and used it to kill several remaining cybermen. This is their last appearance in the original show.
This is Cybermats first appearence in the revived series. This version have very sharp teeth and have seemingly organic mouths. They are used by the Cybermen to supply power to a crashed Cybermen ship in a shopping mall. The Doctor managed to stop it, and revert it to use against the Cybermen, but it was destroyed when a Cyberman crushed underneath its foot.
Nightmare in Silver
A new type of Cybermat appears and has new abilities. The are microscopic in size and are great in numbers. They can also partially upgrade people and can reactivate inactive Cybermen. Because of their actions thousands of Cybermen are able to return from Cyber tombs who also are more advanced. In the end the Cybermen and Cybermats are only stopped by the destruction of the planet that they are all on. However in the end it is shown that one Cybermat survived on a rock floating in space. It is likely that it is responsible for the return of Cybermen since more Cybermen are shown in later episodes.