Tribbles hail from the far reaches of Federation space. They are small creatures with an amazing capacity to reproduce at speed. Their bodies, which resemble flattened spheres, are covered in fur that varies from pure white to darkest black through several shades of tan and brown.

It is not immediately obvious which end of a tribble is which. Indeed, it is debatable whether tribbles have a head as we would think of one at all; they certainly have no teeth. They possess only a rudimentary intelligence. They emit squealing noises when sat or trod on,  indicating that they can feel pain; they can also differentiate between various humanoid species, but exactly how they do this is unknown. As well as having no differentiated limbs or head areas, tribbles are also asexual.

The is only one tribble gender, and the creatures can reproduce at will. Their rate of reproduction, and the speed at which they eat, is so fast that a single tribble can pose a very real ecological threat to a planet`s environment; it virtually creates a plague.

Tribbles are born pregnant, and reproduce at an alarming rate. The average tribble can produce a litter of approximately 10 offspring every 12 hours - leading to more than a million young tribbles in less than three days. This may seem excessive, but is a necessary survival strategy on their homeworld. The environment from which the tribbles originate is riddled with predators, and few offspring reach maturity; this level of reproduction serves to perpetuate the species, but little more. It is only once tribbles are removed from their natural habitat and introduced to one that is free from predators that their rate of reproduction becomes a problem.

Baby triibbles are approximately three centimeters in diameter; an adult tribble may grow to as much as 30 centimeters in diameter.

Fifty percent of a tribble`s metabolism is geared for reproduction. Tribbles sole purpose in life appears to be nothing more than to eat and to breed. They seem to be able to seek out food anywhere, and can reach it by moving through vents, machinery and even up walls; tribbles can stick to seemingly smooth vertical surfaces with the skill of a spider. If their food supply is limited their ability to breed is diminished, and starving them is often the easiest way to limit their growth. However, left to their own devices tribbles will reproduce at an incredible rate.

Many intelligent species find tribbles attractive, and they are often sold by intergalactic traders as pets or souvenirs. When held or stroked, tribbles emit a low, gentle purring noise which has a tranquilising effect on the nervous system of humans and many other races. They may also rock gently in time with their purring.

However, the tribbles ability to breed so quickly turns many a charmed tribble owner against his or her little pet and, as Dr Leonard McCoy once remarked, there is no practical use for the creatures. Indeed, there are races who consider them to be vermin.

But there are few races that are as virulent in their hatred of tribbles as the Klingons. This proud warrior race describes the tribbles as `detestable creatures` and, in the late 23rd century, decides that enough is enough. Hundreds of Klingon warriors are sent out to rid the Galaxy of tribbles, and a Klingon armada obliterates the tribble homeworld.

This would have been the end of the story if not for Arne Darvin, a Klingon spy who, in 2373, travels back in time to the Federation starbase Deep Space Station K-7 in the year 2267. Darvin`s attempts to alter time are foiled by staff from the 24th-century station Deep Space Nine, but when the Starfleet officers return to their own time they inadvertently bring a tribble with them. Soon Deep Space Nine, like K-7 more than a century earlier, is deluged under a sea of tribbles.