Bee

Bees are a species of insect some of which are native to Earth.

In 2009, while researching strange occurrences, Donna Noble noticed that the bees were disappearing. When she told the Doctor about this (on two separate occasions), he agreed that this was odd. (DW: Partners in Crime, Planet of the Ood)

Bees were also disappearing in the alternate reality where Donna had turned right instead of left. (DW: Turn Left)

The disappearing bees were actually a sign that Earth was about to be stolen via Transmat by the New Dalek Empire. The bees were disappearing because they were returning to their homeworld, though the Doctor claimed that not all bees were aliens. (DW): The Stolen Earth)