In this article, I am going to talk about a very controversial topic: Bristleworms in saltwater tanks. What are they? Can they harm your corals? Are bristleworms dangerous to the fish, snails, shrimp, etc.? Are they pests in the tank? Should you remove them? How to remove them if necessary? And many others.
Right from the start, I would like to say that many species of bristleworms are quite harmless and even make amazing detritivores that help the reef aquarium process uneaten food. Although it is only a small minority that can cause trouble, aquarists often do not want to take any risk and see them as ugly pests anyway.
So, are Bristleworms much underrated as pets? However, before we start we need to understand what we are dealing with and what and who are the true enemies in our tanks.
What are Bristleworms?
Bristleworms are a diverse group of segmented worms. They belong to the class of Polychaeta which in Latin means “Many hairs”. Their body consists of many segments, where each part has a pair of fleshy bristles, which are made of chitin. These bristles run down either side of the body of the worm.
Bristleworms are globally distributed, reaching its highest diversity in shallow tropical and subtropical waters. In nature, bristleworms can be found at all depths, including abyssal areas and a few species have been recorded even in polar regions.
Behavior of the Bristleworms
Bristworms are nocturnal. They usually hide and/or burry into the substrate during day time that lets them stay unnoticed for a long time.
Some species are so good at this hide and seek game that they can grow huge still being undetected.
In general, bristleworms in our tanks belong to peaceful species and will not harm neither corals nor fish. However, it is not always sunshine and rainbow. In the most terrible cases, the first time aquarists find out about them when the population of their fish and shrimp colony starts decreasing without any obvious reason.
How do we Get Bristleworms in our Tanks?
Bristleworms are excellent hitchhikes, so, it is very easy to accidentally introduce them into the tank. They can spawn from bacterial particles, life rocks, and corals. Sometimes bristleworms can come even with new fish, snail or shrimp. To be precise, in the water bag from a seller.
Once bristleworms are in the tank, they make themselves at home easily. To tell the truth, most aquarists accepted them as inevitable evil or a natural occurring item in the hobby. So, if you are running your tank for a year or more it is almost a guarantee that you have a bristle worm colony in the tank. Maybe you do not know about it yet.
Taxonomy and Identification of Bristleworms
Well, it can be very difficult to identify what species of bristleworm we get in our tanks. The problem is that there are more than 10 000 species of these worms and every year new species are found and described.
However, to be honest, most aquarists could not care less about it. After all, we are not planning to keep and breed them on purpose.
So, what we really want to know is what types of these worms most often found inside our aquariums and what we can expect from them. That is why aquarists have classified all bristleworms into 2 main categories:
- the good bristleworms.
- the bad bristleworms (Fireworms and Hobbit worms).
Bristleworms and Fireworms
Once again I need to repeat that this classification is conditional and only reflects the interest from a reef aquarists’ perspective because all Fireworms and Hobbit worms are also bristleworms.
- Aquarium good bristleworms. Benefits
As I have just said, most of bristleworms we hobbyists encounter are generally harmless and beneficial scavengers or detritivores. In the aquarium, they consume materials (like uneaten leaves, food, waste or dead fish, shrimp, snail, etc.) that would otherwise decompose and produce ammonia.
Another positive aspect of having bristleworms in the tank is that they eat algae. In fact, some aquarists gladly invite them into their reef tanks to help keep down the algae.
They will not bother any corals and can co-exist peacefully with your reef tank. In addition, they help keep the substrate stirred. All in all, lots of aquarists consider them as the best clean up crew.
Although their bristles do not cause a lot of harm, many of the beneficial species can also sting as well. Even if they do not pose a serious threat to your fish or invertebrates, it can still irritate the skin. That is why most fish prefer to avoid them.
Appearance: often pinkish or gray in color. Their bristles are not thick. It may often seem like they do not have them at all. The body of these worms is slender compared to Fireworms.
- Aquarium bad bristleworms aka Fireworms
Large tropical species of bristleworms are normally colorful and commonly referred to as “Fireworms”. According to different studies, some species of the Fireworms have hollow calcareous harpoon-type chaetae (bristles) containing neurotoxin(s) or complanine (an inflammatory substance), that cause intense irritation on skin after penetrating the skin of anyone handling them roughly.
Although these bristles are not lethal to humans, people describe it as being close to the average bee or wasp sting.
However, what is even more important, these species can be predatory and are not compatible with corals. They can cause some problems to corals that can irritate the base of corals, clams and things like that. Basically, this is the main reason why people hate them.
Appearance: These worms look bulkier and stout with the bright white tufts of bristles.
Although Bristleworms and Fireworms look very similar, we can see the difference if compare them side by side.
|Difference between good Bristleworms and Fireworms|
|Body size||Up to 2 – 7 inches (5 – 15 cm)||Up to 3 – 10 inches (3 – 25 cm)|
|Body-color||Gray to pink||Reddish color near the bristles|
|Bristles||Barely visible||Clearly visible white|
|Sting||Yes (weak)||Yes (strong)|
Note: In some articles, you can find that Fireworms are also more aggressive eaters and generally less shy compared to other bristleworms. In my opinion, it depends on the species and the size of the bristleworms. When they are small they all prefer to hide, therefore, I would not use it as a dead giveaway that it is a fireworm trying to steal a snack.
Nonetheless, if it is difficult to tell the difference between “good” bristleworms from “bad” fireworms, I would follow the rule – if in doubt, throw it out!
Fireworms and Coral Predation
Hermodice carunculata (the Beared Fireworm) is a widespread and abundant corallivore in tropical and temperate seas. It is a well-known predator of the anemones, fire corals, zoanthids, etc.
According to the study, researchers investigated coral predation (Montastraea faveolata and Agaricia humilis) by three different size classes of Fireworms under laboratory conditions. The results of those experiments will upset any aquarist.
- Small-sized Fireworms were more dangerous to corals! Coral had the lowest probabilities to survive in the presence of small-sized fireworms (only 2 % on day 4 for both coral species).
- Mid-sized Fireworms dealt less damage. Survival probabilities increased to 42 % and 54 % accordingly.
- Large-sized Fireworms were less harmful to corals. Survival probabilities of the corals increased to 93 and 90 %.
Why small-sized Fireworms turn out to be more harmful?
A number of studies on marine organisms, in our case Fireworms, show that they choose to feed on coral not because of foraging experience but represent an adaptation to choose prey in habitats protected from predation. Once they become large enough, they change their behavior in a search for other prey as well.
Fireworms and Other Predation
Fully-grown Fireworms can become pretty aggressive to anything in the tank. It seems like the fact that they are still smaller than their prey, do not bother them at all.
For example, the Beared Fireworms can also prey on various starfish and even the sea cucumber. They were observed preying actively on a specimen of the sea cucumber during a 15-minute period. The sea cucumber was 40 cm (16 inches) long, while the worm was only 15 cm (6 inches).
These evil creatures have been known to attack even perfectly healthy fish at night when the fish is sleeping. There are countless reports of them hunting down all snails in the tank.
Hobbit worms (Eunice sp.)
This is the 3rd type of bristleworms that you can get in your tank. Although these monsters can grow up to 3 meters (or 9+ ft), they are absolute champions of disguise. They can live for years in the tank without being noticed. Years!
Hobbit worms are ambush predators and hunts by burrowing the whole body into the sand (or hiding in the tiniest crevices) and waits until nearby prey is picked up on one of its sensors.
These worms are very fast, smart and cautious. Even if you know that it is there it is almost impossible to catch manually. Because of its size, the traps usually do not work against it as well.
The only option is to remove the rock and deep it. In the worst-case scenario, people had to dismantle the tank to find it and get it out.
What Do Bristleworms Eat in Aquarium?
In respect to feeding habits, bristleworms are generalist species that are both omnivorous and opportunistic scavengers. In aquariums, their diet mainly consists of algae, leftovers, and fish waste.
Bristleworms are excellent scavengers and able to get into all the crevices of the live rock that most other clean up crew cannot reach.
Bristleworms Prey on My Snails?
In most cases, bristleworms scavenge tank inhabitants dead of another cause. However, from time to time we can see that even ordinary bristleworms are also accused of killing healthy snails, inverts and even fish. Is it so?
When a snail falls and lands upside down without a way to flip back over it, it becomes an easy meal.
Personally, I tend to agree that some rare species of bristleworms (remember that there thousands of them!), when they get big and hungry, can go in “Rogue mode” and start killing snails, small hermit crabs, etc.
Does it happen often? No, it does not but we need to be aware of it anyway.
How to Prevent Bristlworms from Getting them into the Tank?
So, let’s imagine that you do not want them in your tank anyway and you absolutely do not care about their beneficial nature to the reef tank.
How can you get rid of any bristleworm species before they even get into your tank? The best way to keep them out of your tank is to head off the problem before it takes hold.
- Buy your corals and live rock from a trustworthy source.
- Every time you buy something, always dip and/or quarantine it!
- Check and double-check everything especially live rocks. I seriously mean it.
To quarantine the live rocks, you will need to set up a separate, cycled, quarantine tank. Some aquarists add some food and check on the tank periodically to see if it looks like that the food has been eaten by something else there.
Note: Ideally, corals and live rock should be left in quarantine for at least 1 month.
Besides unwanted hitchhikers like bristleworms, snails or hermit crabs, which are mostly harmless, the quarantine will also help you to avoid introducing something really dangerous, for example, mantis shrimp or Bobbit worms.
There are many good products on the market right now, for example, Seachem Reef Dip – link to check the price on Amazon.
- Remove 4 L (1 US gallon) of water from the source aquarium to a container suitable for dipping.
- Add 5–10 mL (1–2 capfuls) of Reef Dip™ and mix.
- Place the rock or coral specimen in dip for a few minutes. Depending on the severity of the In very severe cases, a double dose may be used.
- Shake them around with forceps or something similar every few minutes.
- Rinse it with clean saltwater and Move it back to a quarantine tank.
- Discard the coral dip. Never reuse the coral dip.
- Repeat after 5 or 10 days. If you are methodical about it is possible to run a bristleworm free tank.
It will disturb all bristleworms so much that they will crawl out of the live rock or frags and flop around in the dipping container.
Some articles suggest dipping live rock in a bucket of dechlorinated freshwater for just a few seconds to remove bristleworms out of it.
DO NOT do that!
Yes, dechlorinated freshwater will shock and/or kill bristleworms and they will pour out of the rock and into the bottom of the bucket but it will also kill all beneficial bacteria needed for biological filtration as well.
Warning: Do not pick up dead bristleworms with your bare hands. The “sting” is like handling fiberglass insulation. It is advised to wear gloves when dealing with all types of bristleworms to avoid coming into contact with their stinging bristles.
How to Remove Bristlworms from the Tank
Let’s say you already have them in the tank and it is too late to quarantine or dip. What other options do we have to remove them from our tanks?
- Physical removal (Manually and by traps).
- Biological removal (Natural predators).
Important: Keep in mind the reason you have so many. Reduce feeding and the numbers will decrease! If you remove the bristleworms without reducing feeding the population will just explode again.
Manual Removal of Bristleworms
Right from the beginning, I would like to start off by saying that this is not the best method. Bristleworms are nocturnal and pretty fast. So, to catch them manually, you will have to turn off lights in the aquarium and in the room and use the flashlight or some kind of nocturnal bulbs.
Now ask yourself, can you catch these little suckers with your gloved hands or a net in a dark room? I do not think so. Therefore, unless they are swarming in the tank I would skip this method.
Note: It can be a viable method only when you have an infestation of bristleworms. In this case, they become so hungry, that they stop hiding anymore.
Traps vs Bristleworms
There are all kinds of traps both commercially manufactured and DIY (do-it-yourself) that you can use to catch them. Of course, it will take time for you but it will definitely work out! However, do not expect fast and easy victory here.
You can find lots of different descriptions of DIY traps against bristleworms. Almost all of them have the same principle. However, if we do some slight changes to them (#3 and # 7), the efficiency will be way higher.
Bristleworm DIP Bottle Trap
- Take a plastic water bottle.
- Cut off the top of the water bottle.
- Fill it with some reef-safe rocks.
- Put the top end of the bottles in the bottom half upside down.
- Drill a hole in the cap for the bristleworms to get in.
- Poke small holes into the top of the water bottles. It will release more smell and attract more bristleworms.
- Cover the bottle with something dark.
- Place fresh seafood bait in a nylon stocking.
Note: Do not simply take the cap off. The smaller the hole is the harder it will be for the bristleworms to actually find a way out of the trap. In addition, you can insert an airline tubing in the cap to make it harder to escape.
Why adding rocks and dark/ opaque bottles make a difference? Because of the nature of the bristleworms! They like darkness and prefer to hide whenever it is possible. They do not like empty spaces (empty and transparent bottles).
Therefore, once they are full, they will try their best to get out of an ordinary trap. However, in this trap, they have lots of places to hide and stay ‘safe’ with the food nearby.
Biological Removal of Bristleworms (Natural predators)
This can be the next way of protecting your reef tanks if you do not want to bother yourself with manual removal or you can combine both to improve the results.
Arrow Crab (Stenorhynchus setrcornis)
Arrow crabs are known to feed on bristleworms. They only problem is that they can be pretty aggressive and predatory. So, be very careful with them if you have small fish, snails, shrimp or hermit crabs.
In addition, some aquarists report Arrow crabs picking at corals when hungry. Therefore, you do need to calculate all the pros and cons before adding Arrow crab. Otherwise, your cure can become even worse than the disease.
Coral Banded Shrimp (Stenopus hispidus)
Coral banded shrimp are excellent bristleworms hunters. Unfortunately, they also do not do well with other ornamental snails, shrimp or fish. They are territorial and will not tolerate any other CBS in the tank.
Olive Snails and Bumble bee snails
Olive snail is also known as “Bristleworm eating snail”. However, they might prey and feed on other snails and clams when hungry.
Bumblee bee snails are also carnivorous but they are small and not very active. Therefore, even though they can catch bristleworms, it will not be systematic.
Neon Dottybacks (Pseudochromis aldabraensis)
Despite their relatively small size (up to 3.5 inches or 9 cm), Neon Dottyback are voracious bristleworms eaters. They have a reputation for feasting on bristleworms. The only downside is they can be temperamental.
It is not advisable to keep them with other invertebrates and smaller fish. They are territorial and can bully other fishes in the tank if they are not big enough to hold their own in the tank.
Melanurus Wrasse (Halichoeres sp.)
Many Wrasses of the genus Halichoeres will readily eat bristleworms. However, they grow big (up to 6 inches or 15 cm) and can be also too aggressive to other tank mates.
Bird Wrasse (Gomphosus varius).
Bird Wrasse reach an impressive size, up to 10 – 12 inches (up to 25 – 30 cm) in length. They are known by their color and distinct nose shape that let them reach between branches of coral to find crabs, shrimp, snails, and other mollusks.
Basically, besides bristleworms they will go after any small (up to 2 inches or 5 cm) long skinny fish, as well as any and all crustaceans in the reef tank.
Harlequin Tuskfish (Choerdon fasciatus)
The harlequin tuskfish is a carnivore with an average size of about 10 inches (25 cm). This is another natural predator of bristleworms. Unfortunately, they will definitely eat your shrimp and most of your clean up crew.
Important: As we can see, almost none of these bristleworms hunters can coexist with each other for a prolonged period of time due to predatory nature. We have to be very careful in our ways to solve the pest problem if we do not want to unleash terror in the tanks.
Safety Measures – Wearing Gloves
In addition, bristleworms are not the only thing in your tank that can cause you harm. For example, it is very easy to get cut, especially if you also have vermetid snails on your rocks which can cut you easily. So, yes, it is important to always wear gloves and if you are not using gloves, at least be very careful where you put your hands!
Warning: I will repeat, it is advised to wear gloves when dealing with all types of bristleworms to avoid coming into contact with their stinging bristles.
How to Remove the Bristleworm Needles?
First of all, do not try to rub them off! Although the bristles are rather harmless, they will still irritate your skin if they penetrate a little bit deeper. This skin reaction is indicative for chaetae piercing the skin and harming deeper integumental layers.
A proper therapy after such injuries is accordingly:
- to remove the chaetae with the sticky side of an adhesive tape.
- to soak the skin in vinegar for little more than 5 – 10 minutes. They will simply dissolve.
Do not use tweezers to remove the bristleworm needles. It will take a lot of time but what is even more important, this method is pretty ineffective.
Most bristleworms have harpoon-like bristles. They are very fragile, so you will simply break them with the tweezers leaving the part of the bristle under the skin.
Important: If the irritation persists for more than a few days, I would definitely recommend visiting a doctor.
How do Bristleworms Reproduce?
Bristleworms reproduce sexually and asexually in our tanks.
Asexual reproduction is accomplished by body separation. The body breaks into two or more parts and the body parts then regenerate heads or tails or both. Therefore, if you cut the bristleworm in two parts, you will get two worms in your tank instead of one.
Sexual reproduction is accomplished by releasing eggs. Once the eggs reach maturity, females will release them into the water. Males and females do not die after mating. Larval development takes about 3 – 4 days.
Bristleworms are pretty common sight in most reef tanks. Although they might look nasty, many aquarists have grown to like and appreciate them because, for the most part, they are a beneficial component of the cleanup crew and fantastic at eating any detritus in the sand or rocks and aerating the sand.
Unfortunately, there is a stigmatism surrounding them because of their appearance. In addition, some people still confuse them with the one notorious species (Hermodice carunculata or ‘The bearded fireworms’) and try to remove all of them altogether.
While Fireworms are major predators of both soft corals and hard corals, common bristleworms rarely bother anybody in the tank. The problem can happen when the infestation completely gets out of control and they get big enough to roam for food in huge numbers.
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- Predation on coral settlers by the corallivorous fireworm Hermodice Carunculata. Coral Reefs. 2012 DOI: 10.1007/s00338-012-0969-x
- Chaetal arrangement of the fireworm Eurythoe complanata (Pallas, 1766) (Amphinomida). Poster. 2016
- Getting to the root of fireworms’ stinging chaetae—chaetal arrangement and ultrastructure of Eurythoe complanata (Pallas, 1766) (Amphinomida). Journal of Morphology. 2017 DOI: 10.1002/jmor.20680
- Revision of Hermodice Kinberg, 1857 (Polychaeta: Amphinomidae). Scientia Marina. 2011 DOI: 10.3989/scimar.2011.75n2251
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- On the occurrence of the fireworm Eurythoe complanata complex (Annelida, Amphinomidae) in the Mediterranean Sea with an updated revision of the alien Mediterranean amphinomids. 2013. DOI: 10.3897/zookeys.337.5811 · Source: PubMed