Bristle worms are considered a pest in every book, trade show, personal conversation, seminar, public speaking and so on. Although I have noticed a few times on this forum, people say that they are ok to have. If so, why are they ok to have? I don't dismiss anything once I understand the reason.
Actually in most reading, they put bristle worms under desease! Bristle worms come in many shapes and sizes. some as small as a few cm and some species that reach over 20 inches. I have lost clams due to them crawling into their siphons and consuming the beautiful creature inside out. They consume every thing with no regard and are not effected by coral defenses, like stinging.
They are unusual creatures in that if you try to remove them while they are half way into a rock the part remaining will heal grow an end and reproduce emediatly. They can over come a system in months. They reproduce sexually and asexually. So if there is just one they are still able to come back. Once you have them it is routine mantainence to remove them. To see how bad you have them. At night sneek up to the tank quietly, they can detect vibration so don't come to slow. look at your aquarium and they are chewing on something.
It is simple to remove them. take a 1-2 inch pvc pipe cap both ends, drill holes big enough for the bristles to fit into. Bait with meat, place in the tank before night and retreave it before light. The worms will have taken the bait and ate it got to fat to get out and bamm! You rid of the pest in a bucket and burry it in a hole outside. Don't touch them, they sting and bite and it is very painful in most species. To make the catch more bountiful bait many traps in the same night. Remove the next morning because you don't want to cause a huge ammonia spike. Repeat this proccess until you catch nothing. Also repeat every few months, since it is unlikely you will rid the tank completely.