The bug is played as an ace unless is can be used as missing card to complete a straight or flush. For example, the hand K-K-X-5-2 is just a pair of kings (with an ace kicker), but any four same-suit cards with a bug make a flush, and a hand such as 7-X-5-4-3 makes a straight.
In draw poker, when a bug is in play, this makes the highest possible hand fives aces, rather than a royal flush, and also increases the odds of improving a hand when drawing to three of a kind with an ace kicker.
Categories: Poker gameplay and terminology