Often, when I'm cleaning my aquarium, I run into bristle worms. The first time I ever found them in my aquarium, my mind ran wild with the evil things these foreign looking worms could do in my aquarium. They can be kind of freaky to run into if you've never dealt with them before, but before you panic there are a few things to consider.
First of all, what is a "bristle worm" exactly?
You might have seen pictures or heard of them before, maybe you've even dealt with them directly. "Bristle worm" is a term that casually describes many types of worms in the class of marine worms referred to as Polychaeta. They are segmented and they have bristles. Good stuff.
The bristle worms that aquarists need to watch out for, in general, are the ones referred to as Fireworms. These worms usually appear in your aquarium as red, segmented and bristle covered. They can range greatly in size, from being so small that you need a tweezer to handle them, to being several inches or more in length. You might only see them at night, at least that's the only time I see them in my aquarium.
Are they bad? They can be. They can also be good. Bristle worms will eat detritus and other stuff you typically might need to manually remove from your aquarium, so they're good in that regard.
However, they can also attack corals and fish if they are big, aggressive or hungry.
Personally, I like to leave the small bristle worms that I find in my aquarium. I've noticed small bristle worms in my aquarium for more than a couple years now. The worms I've seen have not grown bigger than a couple inches, at most. They do not appear to bother any of my other inhabitants. That's okay with me. If they're not upsetting my aquarium balance, and if they eat detritus, why not leave them in there for now? At least that's my current opinion.
The first time I found small bristle worms I tried trapping them for a while with one of those small, green tube traps that can easily be found at most fish stores. It worked, I trapped a lot of little red bristle worms, but after a while I realized I'd rather be letting those bristle worms eat the junk that settles on the bottom of my aquarium rather than eating my bait.
I think each aquarist needs to evaluate the situation in their own right. If you're on the fence about what to do with bristle worms in your aquarium, it's probably best to remove them.
If you're like me, and you haven't seen any other negative effects on the rest of the aquarium inhabitants from existing bristle worms, you're probably okay leaving them if you want to. Just keep tabs on them and make sure they don't overrun your aquarium or grow to sizes where they do become a danger to other inhabitants.
If you decide to remove them from your aquarium, here's a few tips:
Don't touch the bristles, they can sting badly. Wear rubber gloves.
Traps can be bought or made. The trapping concept is pretty simple, lure them into a container, using bait, that the worms can enter but not exit.
Inspect live rock before adding it to your aquarium to help prevent hitchhiking bristle worms from getting into your aquarium in the first place.
You can get critters that eat bristle worms. Dottybacks, various wrasses and coral banded shrimp are a few examples.