If you have ever seen a bristle worm in your reef tank, you would probably agree they can be ugly little creatures. I’m pretty sure we’re genetically programmed to be creeped out by millipede-looking creatures. There is a lot of energy and discussion about this lowly polychaete in reef aquarium circles. The bristle worm is a live rock hitchhiker that reef tank owners love to hate. Is there merit to the debate, or is it a bit over-blown?
Let’s dig into the topic and see if we can separate the dirt from the detritus.
If you have a specific question and want to jump right to that section, you can do so, here:
- What do bristleworms eat?
- Where do bristle worms come from and how do they get into your tank?
- Can bristle worms kill fish?
- What do bristle worms do?
- Are bristle worms parasites?
- What happens if you touch a bristle worm?
- Are bristle worms dangerous to humans?
- Are there good and bad bristle worms?
- How do I get rid of bristle worms in my tank?
- What eats bristle worms?
- Should I get rid of bristle worms?
A bristle worm is a small, cryptic segmented worm that often lives in the live rock and sand of a reef aquarium. They eat detritus and decaying stuff in the tank. This is what they look like when they are small:
They belong to a family of segmented worms called polychaete, which means ‘many hairs’ in Latin. The family name would be olychaetep in Pig Latin, of course, but I don’t recommend using Pig Latin, if you want to impress–or even keep–your friends.
The hairs are what give this polychaete its common name. If you look closely at some of the larger pictures on this page, you can see that each segment on its body has bristles sticking out of both the left and right sides. Those hairs protect the worm from predators…and your fingers…if you stick your hand in the tank without thick gloves.
Bristleworms are detritivores. That means they dig through the muck, gunk, and detritus in our tanks and eat the stuff that is rotting away and spoiling the water quality. Their preferred food is food waste, biological waste, even the rotting carcass of that missing damselfish you haven’t seen for a few days. Any of those items would proudly anchor the menu at Chez Bristleworm–but good luck getting a table on the weekend. Any of those items, if left to rot, would otherwise add ammonia, nitrites, and nitrates to your aquarium water–spoiling those pristine water parameters you work so hard to maintain.
Most of us happily pay good money to add a cleanup crew to our reef tanks. So why is there so much fuss about this pesky polychaete?
Some of it, likely, is from a negative stigma associated with the fact that they dine on our biggest disasters–but let’s continue exploring the many aspects of this many-haired worm.
The most likely scenario is that they found their way into your tank by hitchhiking their way in on a piece of live rock. As mentioned earlier, they are nocturnal creatures and spend their days hidden inside the many crevices within live rock. In general, rocks don’t tend to move on their own–so it’s a pretty good strategy–unless, of course, that rock is headed to an aquarium store or someone else’s reef tank.
I’ve even seen them attached to live rock rubble or small coral frag plugs.
Bristle worms are scavengers that eat left-over food and dead stuff in your aquarium. If you happen to see them in your tank eating a dead fish or dying coral, it is very likely the animal died first and the smell of decay drew the bristle worm to the feast.
These pointy polychaetes do the job that nobody else wants to do. They are the cleanup crew that removes the dead bodies and decaying biomass in the tank. No kidding. They do the work that a cleanup crew should do, with none of the fanfare and none of the fame.
No, the common bristle worms you may find in a saltwater tank are not parasites. They are detritivores, meaning they sift through and eat things in the detritus, including dead and decaying matter.
A parasite, by comparison, lives in or on a host and feeds off the host. There are other parasitic polychaetes in nature, but the common critters in your tank are not likely to be them.
The vast majority of bristleworms you are likely to encounter in a saltwater aquarium are regular old polychaetes that are NOT dangerous to humans. However, there is a small chance that a more dangerous species (the fire worm) made its way into your tank. It is a good idea to wear thick gloves when you have your hands in your tank anyway.
While the nature of this article isn’t intended to delve into the ontological merit of these organisms or the philosophical value of a cleanup crew detritivore on the food chain (um, what?), but the simple answer is that, from a self-interested reef aquarists’ perspective, yes, there are good and bad bristle worms. Luckily for us, the most common variety is the good kind, and the bad kind is very rare.
Here is a video that shows the difference between a good and bad bristle worm, side by side:
And another video that shows the predatory behavior of one of the bad bristle worms:
Having too many bristle worms in a reef tank is a symptom of a bigger problem, not really a problem of its own right. You see, if you have a ton of bristle worms, it means you have a ton of dead animals or left-over food rotting in your tank. Because without all that food, you wouldn’t have all those bristle worms. So in one way of thinking about it, the bristle worms are a very, very good thing—because, without them, you’d have very foul water. Instead of having polluted water, you have a zillion bristle worms.
Touching a bristle worm is a lot like touching a small cactus or getting a series of splinters. The tiny hair-like bristles will get stuck in your skin and have to be removed with tweezers. The affected area will be tender for a while. Here is an image of me pulling bristles out of my finger.
Bristleworms may be in your sand or under your live rocks, usually in places you can’t see. That is one of the many reasons why it is important to always wear gloves, when you have your hands inside the aquarium.
Yes. Those are my hands. You can read about that fun experience here.
There are three primary ways to get rid of bristle worms:
- Physically remove them when you see them (remember, don’t touch)
- Trap them
- Add a predator to eat them
Physically removing them
You need some sort of grabbing or scooping gadget to remove them safely without getting stuck. But the process is fairly straightforward. See ’em, get ’em.
Building your own DIY bristle worm trap
I’ve included two potential designs to make your own bristle worm trap using plastic stuff around your house.
DIY Soda bottle conversion
The soda bottle conversion is a classic design you can use to trap lots of underwater critters.
Step 1: Cut off the top of the bottle with scissors or a knife
Be careful, the plastic edges will be sharp!
Step 2: Unscrew the cap, invert bottle so that the smaller opening is inside the body
Step 3: Super glue or silicone the sides so that bottle trap is completely sealed
Step 4: Place some rotting, stinking bait inside the trap. Place the trap on the bottom of your tank and go to sleep.
See what you can catch the next morning. You may need to weigh the trap down to get it to stay in one place. The basic premise of the soda bottle design is that the worms will climb in to get the free meal and some/most won’t climb back out…hopefully.
DIY food storage container conversion
I also found a DIY bristle worm trap design on Reef Builders that involves taking a small, rectangular food storage container with a lid. You cut an X pattern into the center lid with a box-cutter tool or a sharp knife. As a result of cuts, you will create 4 triangularly shaped flaps (that are sharp now, be careful). By bending those flaps inward, you create a similar funnel design where it is easier to get in than it is to get out.
Step 1: Cut an x through the top of the lid, creating 4 sharp, plastic triangles/pyramids that flex in the middle
Step 2: Push each of the parts down and bend them so that you create a semi-permanent gap large enough to catch some worms.
Step 3: Bait your trap, set it on the bottom of your tank and see what you get
Just because you could remove the bristle worms doesn’t mean that you should. That is a decision that only you should make–but since you asked–I’ll give you my perspective on the matter. Bristle worms are ideally suited to aquarium life.
That’s why they grow and reproduce so well in our tanks. It would be rare and unusual for an aquarist to pay money, intentionally, for a bristle worm. We don’t invite them into our tanks, they just show up. But many of us (I’m raising one guilty hand right now) is a little bit sloppy with our husbandry; we feed a little too much and clean the tank a little less often than we should.
The bristle worm population in your tank helps create a little bit of a natural, biological buffer–a cleanup crew that you didn’t intend, but mother nature developed specifically for this purpose. In addition to that, think about all the biological diversity and invertebrate life going on in your tank. How many rotifers, copepods, stomatella snails, hermit crabs, starfish, and other snails live and die in your tank in a given week, month or year?
I suspect you’re pretty good about removing large, dead organisms, like an unfortunate fish–but what about all those other critters? Do you catch and remove them all? Or do you need (or want) a little help?
The bristle worm is nature’s cleanup crew, so my vote is that you leave them alone. Monitoring the population should give you some insights into how much waste is really in your tank (and free for the bristle worms to consume), but otherwise, these segmented polychaetes are a good thing, in most tanks. The only time I would recommend removing them is if you have the larger, problematic species–or if you absolutely just can’t stand the sight of them.
Photo credit: Prilfish
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