Bee

Bees were "insects [...] with stings on their tails" according to the Fourth Doctor, and a non-sentient species found on Earth. They were domesticated by humans for the production of honey, and even an average human like Donna Noble knew that they were experiencing a profound global downturn in their population during the early 21st century. (TV: Delta and the Bannermen, Partners in Crime, Planet of the Ood)

Lifecycle: hives and honey
Many bees lived in colonies, collecting pollen to be created into honey. Bees were domesticated by humans for their honey. They were a hive society with a fertile queen, male drones, and infertile female workers. Bees could make a new Queen to make new eggs. (TV: Delta and the Bannermen, AUDIO: Survival of the Fittest) According to the Eighth Doctor, worker bees gave female bees special jelly, what Goronwy called royal jelly, when they needed new Queens to form a hive. (AUDIO: The Creed of the Kromon, TV: Delta and the Bannermen)

In 1959, Goronwy kept bees. He gave the Seventh Doctor a jar of his rare 1928 hibiscus blossom. The Bannermen invaded his honey store and were covered in the substance; this caused the bees to attack them. (TV: Delta and the Bannermen)

According to the Seventh Doctor, the Vrill had a similar lifecycle to bees. The Vrill Authority had a role quite similar to that of the Queen bee. (AUDIO: Survival of the Fittest)

Disappearance
For some time, Earth's bees lived alongside — and humans never knew that they were different from — visiting, sapient Migrant Bees of the planet Melissa Majoria. When the Migrant Bees suddenly left Earth in the early 21st century, scientists were flummoxed as to the cause of the sudden drop in the bee population, unaware that they were studying the wrong type of bee for an answer. (TV: Partners in Crime, Planet of the Ood, The Unicorn and the Wasp, Turn Left, The Stolen Earth)

Eventually, the Earth's native bee population dwindled to near-extinction levels. However, bees were being reintroduced to the United Kingdom in June 2027, and, according to Ace, the bee problem would be solved by 2040. (AUDIO: A Death in the Family)

Bees and the Doctor
The First Doctor, Barbara Wright and Susan Foreman were startled by a bee that almost fell on them after it was killed by ingesting the illegal insecticide, DN6. Because they were miniaturised at the time, the bee's mass posed a grave risk of injury to them. (TV: Planet of Giants)

The Fourth Doctor professed to be rather fond of bees. (TV: The Robots of Death) Romana I compared K9's greeting to the computer, Mentalis, to the identification dance used by bees. When asked what bees were, the Doctor replied, "Insects! With stings in their tails". (TV: The Armageddon Factor)

Donna Noble repeatedly mentioned the disappearance of the bees to the Tenth Doctor who eventually realised that they were Migrant Bees returning home. He was able to use their Tandocca Scale to help track the missing Earth. (TV: The Stolen Earth)