The Trouble with Tribbles and Other Pests

When Captain Kirk looks desperately at Mr. Spock over what should have been his chicken sandwich and coffee but is instead a pile of cooing hairballs, you can get a sense of how farmers, foresters and researchers sometimes feel about invasive species.

"I want these things off the ship," Kirk says, a little frantic. "I don't care if it takes every man we've got."

The hairballs are tribbles. Lieutenant Uhura buys one as a pet and the crew of the Enterprise quickly discovers tribbles are prolific and soon the little hairballs are climbing the walls, filling the food processors and invading the storage compartments full of quadrotriticale--a valuable grain being taken to aide the Sherman's Planet colony. The tribbles eat all the grain, but die shortly afterwards because it's been poisoned. Shenanigans ensue; the Klingons are to blame; Kirk, Spock and McCoy save the day.

"The Trouble with Tribbles" is a classic episode from Star Trek: The Original Series and provides one of the few well-known examples of invasive speceis in popular television and literature. And, conveniently, tribbles meet most of the descriptions of what makes a species invasive.

A Tribble, A Drabble, A Flood.

Tribbles are what we would call an invasive species. In federal government parlance, that's any "alien species whose introduction is likely to cause economic or environmental harm or harm to human health." Essentially: non-native species that society considers pests or nuisances.

Tribbles meet the qualifications for invasive species almost perfectly:

- Tribbles tolerate a variety of habitats, from their home world Iota Geminoum IV to spaceships.

- Tribbles grow and reproduce rapidly. Mr. Spock says one tribble has an average litter of 10, producing a new generation every 12 hours

- Tribbles compete aggressively for resources.

- On the Enterprise, tribbles have no natural enemy. On their home world, their populations are kept in check by alien lizards.

Aye, they're in the air vents, too.

David Gerrold, who wrote the "The Trouble with Tribbles," says he got his inspiration from an example of the real world damage invasive species can do--rabbits in Australia. Rabbits were brought to Australia in the 1800s for food and sport hunting, but they did so well that they devastated plant life and shouldered aside other, native mammals.

So, the rationale for introducing the rabbits was reasonable enough. As long as the rabbits' usefulness as food and entertainment outweighed the negative effects they had on the environment, people didn't think of them as an invasive species. Species used for food or livestock are considered non-native--but not invasive--species as long as they remain under control in the circumstances for which they were intended. Essentially: non-native species that society considers beneficial.

Back in the twenty-third century on the Enterprise, quadrotriticale fits the definition of a non-native species. It's going to be introduced on Sherman's Planet as a food source for the colonists. Corn, wheat and cattle have been introduced to many areas on Earth where they're non-native, yet not invasive.

Who put the tribbles in the quatrotriticale?

Kudzu, 'the vine that ate the South," was originally brought to Pennsylvania in the 1800s and heavily marketed as a good way to control soil erosion. It turned out to thrive in the hot, humid environment of the South; but without any natural enemies the plant can--and will--grow up to 12 inches a day during the summer. Kudzu changed from a useful, non-native species to a devastating, invasive one. By one estimate, the vine spreads over 150,000 acres annually, swallowing any stands of trees and patches of open spaces in its path. An Auburn University researcher estimated electric companies alone spend $1.5 million annually trying to keep it from choking power lines.

Then there's rye. It's non-native, but farmers think it's a very valuable--$49 million a year--field crop. But along Colorado's Poudre River, conservationists consider it an invasive species because it outcompetes native plants and destroys animal habitat. So while there are guidelines, the distinction between non-native and invasive is sometimes a matter of location.

Some researchers estimate that it costs farmers and governments in the United States $120 billion a year to combat and control invasive species. But farmers also make around $800 billion every year in largely non-native crops and livestock. So in some ways, there is an economic line between non-native and invasive, too.

But when individuals think about the difference, it often comes down to personal experience. Pythons are much-beloved, non-native pets in many Florida homes. They are not so loved by Florida residents who fear for their dogs, cats and small children. Ever since a few snakes escaped their cages and began proliferating and prospering in the Everglades, they've attacked everything including alligators.

You can never know how a species is going to respond when you remove it from its native environment, which is why you should never try to make that judgment call for yourself. Lieutenant Uhura is an accomplished and intelligent officer and linguist. She thought that first tribble would make a good pet, but those harmless looking furballs nearly caused the collapse of an entire colony.

So the next time you take a vacation, whether it's to Japan, Australia or Rigel IV, keep in mind that if the pet or plant you decide to bring home with you gets out of control, we really don't have any Klingons around to foist them off on.

Tribbles make for a good example for a star ship far, far away in the twenty-third century, but let's move on to some twenty-first century Earth instances of invasive species in Southern California.