Acari

The Acari were a sentient arachnid species encountered by the Tenth Doctor, Emily Winter and Matthew Finnegan.

Biology
The Acari look like red spiders with large eyes. They sit inside little space suits. They are related to half a dozen sentient arachnid species encountered by the Doctor. They are not very clever, and once thought a clockwork mouse was a companion of the Doctor. They have a weakness of bug spray, found in the TARDIS garden.

Technology
The Acarai use ships that look like big, rusty spiders. The Acari do not have the ability to travel in fifth dimension space, but they can breach the walls of the TARDIS. They have large rifle like weapons, and space suits comfortable for their bodies.

History
The Acari were used as a disguise for a Gizou agent in plot to kill the Tenth Doctor. An Acari spaceship crashed into the TARDIS, playing havoc with the systems, and with the Doctor, because of his psychic link. The Acari invaded the TARDIS, attacking the Doctor, Emily and Matthew. The Acari ship was taken away when a TARDIS crank got entered in a console, resetting the TARDIS.