Droon

The Droon were a species of parasitic insects, known for living in people's noses.

Biology
When adults, Droon were small, black insects the size of a cockroach, with sharp, barbed limbs. (TWN: Border Princes)

Life Cycle
When arriving on Earth, the Droon found somewhere warm and moist to hide in, generally people's noses. As many as six could be found in one person. They were generally harmless at this stage, causing a cold-like state. Most Droon would leave or die in a few months, but 10% pupated and advanced to their next stage.

At this point, alpha-wave patterns would be emitted. If they weren't removed before finished developing, they would cause harm to the host. They were vulnerable to infrasonic wave at this stage, leading to the creation of the anti-Droon audio paddle. (TWN: Border Princes)

History
The Droon were a migratory species, occasionally coming to Earth via the Cardiff Rift. They frequently hosted inside Humans, and one of Torchwood Three's jobs was removing them. There were 4 removals after 2000 and another 3 after Gwen Cooper joined Torchwood.

When James Mayer was working with Torchwood, Droons were removed from Mr and Mrs Peeters. (TWN: Border Princes)