The presence of the tufts of such large and evident bristles on the common reef aquarium scavengers have given them the name of "bristle worms." This is a perfectly good and very useful common name; it is certainly as valid in this context as any scientific name. Unfortunately, instead of being confined to this one group of worms, the term has become all-inclusive for all mobile worms found in aquaria. Some of these other worms, not as benign as the fire worms, may cause serious problems in tanks. Large eunicid polychaetes, which look superficially like fire worms, may eat fish, and some other large worms may attack clams. If these other predatory worms raise a bit of havoc in a tank, and are discovered in the act, the aquarist claims that "bristle worms" have done the damage, and in the process condemns all bristly worms. Other aquarists upon reading such an account of death and destruction may spend a lot of time and effort to removing beneficial fire worms from their tanks, much to their system’s detriment. Of course, neither eunicids nor clam-eating worms have the large and evident tufts of bristles, and even a cursory examination should have shown these differences. However, both eunicids and clam-eating worms are, of course, worms. Therefore, they must be bristle worms, and therefore all bristle worms are bad. If you agreed with this logic (or even if you didn’t), you should read a short essay by Joel Cohen, titled, "On the nature of mathematical proofs," which shows, rather nicely, that Alexander the Great was white, had an infinite number of limbs, and did not exist. (Baker, 1961) (this book is out of print, but the essay is available on line at: www.cs.berkeley.edu ).
for you lazy people who dont want to click the link and read it.
Somewhere in the dim dark pasts of the reef aquarium hobby, some less-than-astute individual made the leap of logic that went something like this: “If Hermodice is a fire worm, and Hermodice eats corals, then all fireworms must eat corals.” Unfortunately, this leap of logic ends with a resounding “splat” as the conclusion collides with reality. Most fireworms don’t eat corals; in fact, it appears that most fire worms, most especially the Eurythoe and Linopherus individuals most commonly found in reef tanks don’t eat anything that is living. These animals are scavengers, and very good ones, at that.
The fire worms most commonly found in reef aquaria are probably the best members of the so-called “clean up crew” that most aquarists can have. They eat excess food, detritus, and the remains of dead or dying individuals. While they will not attack living and healthy animals, they definitely will attack and eat an animal that is damaged and releasing blood or other tissue fluids. Because they are very adept at following scent trails and very active in their search for food, they will often find a dead or dying animal and remove all traces of it in very short order. Their fantastic ability as scavengers is likely the cause of the myth that they eat living prey. Most marine invertebrates will appear to be healthy all the time they are, for example, starving to death. If the animal finally succumbs to malnutrition, the worms will start to clean it up. If an aquarist wanders in and sees this occurring in a tank, they don’t see some diligent janitors. They see their prize specimen being consumed by some “ugly” worms! And, gasp and gadzooks, they think the worms have killed and eaten it! Well, the latter part of that conclusion is true, but the animal that is now food died of something else. As these worms don’t attack and kill animals, neither do their bristles sting corals or sea anemones, and they definitely don’t crawl up into the cavities inside a tridacnid clam, and start eating it. All of these “definite facts” are truly fine examples of aquarium mythology.
What fireworms do do, and do well, is clean up excess uneaten food and remove the recently deceased. Both of these tasks are of vital importance in reef tanks, as even a little time at reef temperatures is sufficient to turn a recently deed animal into a severely fouled aquarium. The beneficial fire worms are just about the most important animals that are available to aquarists for keeping their systems clean and functional. Perhaps, all an aquarist has to do to realize this is to contemplate the amount of “excess food” that it takes to grow a large population of the worms. Then, they can contemplate, what would happen to all that excessive nutrient if the fireworms were absent. In all likelihood, that food would have rotted and gone to foul the aquarium.
The moral of this little tale is that many hard and fast aquarium beliefs are myths. In this case, in particular, many of the “horrible” worms in reef aquaria are not only highly beneficial, but in most cases, absolutely necessary for the systems.
I think what it comes down to is that kind is bad - Hermodice carunculata. It will eat things in your tank and can get large (I just pulled what I believe to be one that was probably 8" long and as thick as my thumb out of my 16g! I think it is what has destroyed my zoo population and shroom colonies). The other kinds can be very beneficial and you shouldn't worry about them...