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The Acari were a sentient arachnid species encountered by the Tenth Doctor, Emily Winter and Matthew Finnegan.
Biology
The Acari looked like red spiders with large eyes. They sat inside little space suits. They were related to half a dozen sentient arachnid species encountered by the Doctor. They were not very clever, and once thought a clockwork mouse was a companion of the Doctor. They had a weakness to bug spray, found in the TARDIS garden. (IDW: Tesseract)
Technology
The Acari used ships that looked like big, rusty spiders. The Acari did not have the ability to travel in fifth dimension space, but they could breach the walls of the TARDIS. They had large, rifle-like weapons and space suits comfortable for their bodies. (IDW: Tesseract)
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. (IDW: Tesseract)