(FORTUNE Small Business) – Animal Control isn't a topic I'd normally tackle here, but the situation in offices like yours has gotten out of hand. Yes, your company has been invaded. But the creature annoying your employees and sullying your workplace walks on two legs instead of four. It's a boss's pet.

You say that you're the kind of boss who doesn't have one? Think again--and ask around. The only person capable of ending office favoritism (you) is often oblivious to its existence. You may think that everyone loves Gina. But where you see a new salesperson with a winning smile and ready quip, your staff sees an unctuous lapdog.

The cost? Ruined morale and warped incentives. With workers doing multiple jobs to help their companies survive in the current economy, they're more sensitive than ever to favoritism. "Co-workers will wonder about the best way to work their way up the ladder. Should they do a really good job or suck up to the boss?" asks Jody Urquhart, author of All Work and No Say, Ho-Hum Another Day: How to Boost Morale and Increase Productivity (Iconoclast Publishing, 2003). Here's a field guide to help you spot and protect yourself against the boss's pet.

THE PREDATORY PET This cunning character agrees with everything you say, directing his charm solely at you. Colleagues nearly hold their noses when he's around but hide their distaste to avoid offending you. Rather than doing his job, he gets ahead by politicking and pandering to power.

Remember Jayson Blair, the New York Times reporter whose favored position with the paper's top two editors made them slow to pick up on his fabrications and deceptions, staining the newspaper's reputation and poisoning its culture? A would-be Blair can't succeed without an easy mark. You can fend him off by establishing objective performance measures (sales booked, cost savings) for all employees. And assess each worker regularly. A pet's shortcomings should leap out on your balance sheet.

THE FAVORED CHILD It starts simply, with an innocent employee who reminds you of your younger self or maybe your daughter. You take this worker under your wing, and before you know it, she's a savvy confidante who's outshining her peers. You owe it to the company to give her the plum assignments, right? Employees everywhere notice every acknowledgement, bonus, and project you dole out, and become dispirited if they aren't awarded on merit. Relying heavily on someone so much like yourself may actually hurt your business. The best ideas emerge from diverse minds, not clones, so cultivate relationships with staffers for whom you don't feel a natural affinity. Divulge key information on a need-to-know basis, or to everyone--not on the basis of your "comfort" with one worker. And be sure that you reward the full spectrum of skills, not just, say, salesmanship.

THE STAR PERFORMER What boss doesn't love a top rainmaker or outstanding service rep--and reward him? Many experts believe that great executives lavish most of their attention on their stellar performers. Such bosses, say Marcus Buckingham and Curt Coffman in First, Break All the Rules (Simon & Schuster, 1999), don't believe that every employee has equal potential. They recognize that some are more talented than others. "And, yes, they even play favorites," write the authors.

So what's the smartest thing to do with a star? First, understand that fairness doesn't mean sameness. Every employee is different and will feel fairly treated if his differences are acknowledged and accommodated. Your B-level performer can be perfectly happy with a star's getting the best projects--as long as the B player has a chance to shine and be recognized as well.

Employees will repay you with loyalty if they know what's expected of them, have the resources and the chance to excel, feel that someone cares about them at work, believe their opinions count, and know that merit is rewarded, say the authors. If that's the case, you'll have reached the ideal state on the boss's pet issue: Each of your employees will feel like one.