Both bears were set free from the same military establishment that the Giant Rats and Vampire Bats had escaped from.

Bumble Bear was the result of a failed experiment in crossing the DNA of a bear with a honeybee in the hope of producing an aggressive animal that could fly and sting, to be used as a weapon.

However, this failed, and he was in fact a nice friendly chap. Bubonica Bear, however, was on the other end of the spectrum.

She was from the 13TH Century and had been displaced by the Time Tunnel.

Discovered by scientists in Romania, they realized she was a carrier of the Bubonic Plague and had been brought back to the UK to be weaponized.

As it turned out she was patient zero from the original plague era and carried a particularly vicious strain.