Hornet

The Hornets, collectively sometimes known as the Swarm, were an insect species which resembled the hornets of Earth, capable of possessing lifeforms. They lived in the depths of space, but came to Earth by accident where they had multiple encounters with the Fourth Doctor. (AUDIO: Hornets' Nest)

Biology
The Hornets appeared visually similar to Earth's species of Hornet but could alter their size at will. This ability extended to other matter. (AUDIO: The Dead Shoes)

The Hornets fed on negative emotions, which the Doctor believed was because those emotions' psychic vibrations were tastier. (AUDIO: Hive of Horror) The Hornets were able to possess living beings, taking control of their mind. The Doctor described them moving from a body as a black smoke. From within a body they could verbally communicate, even that of an animal usually unable to speak such as a dog. (AUDIO: The Circus of Doom, A Sting in the Tale) The Hornets were also able to influence people by stinging them. (AUDIO: The Dead Shoes) The Hornets could also possess inanimate objects, such as the preserved bodies of dead creatures, (AUDIO: The Stuff of Nightmares) and a pair of ballet slippers, which were left imbued with the Hornets' power as a result. (AUDIO: The Dead Shoes)

The Hornets were a hive-mind, though the swarm was led by an individual Queen who the rest served. (AUDIO: A Sting in the Tale) Without the Queen, the swarm was left in anarchy. (AUDIO: Hive of Horror)

The Hornets were vulnerable to fire and smoke. (AUDIO: The Stuff of Nightmares, Hive of Horror) They could also be pacified via hypnosis. (AUDIO: The Stuff of Nightmares)

History
According to the Doctor's research, the Hornets once ruled a world, resulting in its destruction. (AUDIO: Hive of Horror)

The Hornets were "blown" to Earth in 1039. Struggling to survive they took possession of a pack of wild dogs and a pig near Tilling Abbey. Nuns belonging to the Abbey captured the pig, which contained the swarm's Queen, so the rest of the swarm used the dogs to lay siege to the Abbey. During this the Hornets encountered the Fourth Doctor for the first time, although for the Doctor this was his fourth encounter with them as he had encountered the Hornets in reverse order. Reaching the pig, the swarm reunited in a single dog. The Doctor lured them to his TARDIS, taking them away from Earth. They took possession of him and forced him to take them back to Earth, arriving in Venice in 1768. As he refused to leave the ship. they left the Doctor and outside possessed Antonio. (AUDIO: A Sting in the Tale) Antonio used their powers to pursue his own revenge.

The Hornets used Antonio to set up the Circus of Delights. With Antonio as the ringleader, and the Hornets travelled from town to town, enlisting people to join the circus where they could influence them. They encountered the Doctor again in Blandford in 1812 where he mesmerised Antonio for information. In response the Hornets abandoned Antonio, leaving him dead, and took full possession of tightrope walker Francesca. As the Doctor closed in they compelled her to jump off the high wire to her death. The Hornets remained dormant in Francesca's dead body, and eventually, her mummified feet and ballet shoes would make their way to a museum in Cromer. (AUDIO: The Circus of Doom)

By 1932, the Hornets had possessed the museum's curator Mrs Wibbsey. After being stung by a Hornet, famous dancer Ernestina Stott felt compelled to steal Francesa's shoes from the museum, using the Hornets' power residing on them in her dances. The Hornets used Wibbsey's voice to compell Francesca to dance towards the sea in revenge for abusing their power but she was saved by the Doctor. He and Ernestina returned the shoes to the museum, where the Hornets through Wibbsey shrank them and imprisoned them in a dolls' house. They possessed a China Doll in order to speak with the Doctor while he was inside the house. The Doctor and Ernestina escaped and used his sonic screwdriver and the Hornets' power lingering on Francesa's shoes to return to normal size. The Doctor helped Wibbsey overcome the Hornets and took her away to Nest Cottage in the future. (AUDIO: The Dead Shoes) Though the Doctor initially believed her free of them, the Hornets actually remained dormant in Ernestina, eventually managing to possess her grandson Percy Noggins. (AUDIO: A Sting in the Tale)

Controlling Percy, the Hornets possessed stuffed animals that he repaired at his factory. They used the animals to assassinate prominent individuals, including a Cabinet minister, attracting the Doctor's attention. He lured them to Nest Cottage where he contained them using the TARDIS' force field and hypnotised them to keep them docile, though occasionally the Hornets attempted to kill him especially at night. (AUDIO: The Stuff of Nightmares) Using Mrs Wibbsey, who they still had influence over, the Hornets arranged the summoning of Mike Yates to Nest Cottage via a newspaper ad. (AUDIO: A Sting in the Tale) At night they moved against him and the Doctor so they sought refuge in the basement. (AUDIO: The Stuff of Nightmares) In the morning, the Hornets used Wibbsey to lure them out, (AUDIO: A Sting in the Tale) but the Doctor was able to hypnotise them into docility again. Using his TARDIS' dimensional stabiliser, the Doctor shrank himself, Wibbsey and Mike so they could confront the Queen in person inside a stuffed zebra. The entire hive abandoned their stuffed animals to come to her defence in the zebra, where she attempted to turn Mike against the Doctor. The Doctor helped him overcome her influence and used one of Francesca's shoes and his sonic screwdriver to turn the Hornets' power against the Queen, shrinking her down until she only existed in the Micro-universe. With her gone, anarchy took over the hive enabling the Doctor and his companions to escape, return to normal size and then contain the whole swarm in a forceshield around the zebra. (AUDIO: Hive of Horror)

Escaping and possessing Mrs Wibbsey again in the Doctor's absence from Nest Cottage, the Hornets employed the Demon to capture the Doctor and turn his mind into the Atlas of All Time at Sepulchre. (AUDIO: Sepulchre) After numerous failed attempts to capture the Doctor, (AUDIO: The Relics of Time, The Demon of Paris, A Shard of Ice, Starfall) the Demon finally lured him to Sepulchre by kidnapping Mrs Wibbsey where the Hornets revealed themselves. Working with Mike Yates and the Demon, who he'd convinced to turn on the Hornets, the Doctor tricked Wibbsey into a sarcaphagos where he could transmat the Hornets away from her, sending them to the museum in Cromer on the date it burnt down. (AUDIO: Sepulchre)