Red Bug Parasites (Tegastes acroporanus)

Somehow back in the day, after over five years of having SPS-dominant aquariums, I got my first case of red bug parasites. A local aquarist was tearing down his system and gave me a few corals that weren’t doing well. Turns out, red bugs AND Acropora-eating flatworms (AEFW) infested the corals. Fortunately, I caught the red bugs while the Acropora was still in my quarantine tank.

In the early 2000’s (now I’m dating myself), there was a general consensus in the reefkeeping hobby that red bugs only affected smooth-skinned Acroporas. Hobbyists assumed they did not bother corals like Milleporas or “the green slimer” due to the extra mucus they produce. Although red bugs do tend to prefer certain Acropora (especially Acropora valida, the “tricolor”), most every Acropora species is susceptible. Hobbyists also commonly believed that red bugs laid eggs and had a larval stage. This led to a consensus that three treatments were needed in order to eliminate the red bugs entirely. Although research eventually determined that red bugs are live bearers, I still recommend three treatments just as a safety precaution.

How to Identify:

On Acropora corals that have “browned out” due to red bug presence, the red bugs are rather distinguishable. They are mostly yellow (almost a gold color) with a bright red dot. They are also extremely tiny at around 0.5mm (think a little bigger than the size of the period at the end of this sentence). Unfortunately, they are not easy to see on healthy corals, and they have an ability to hide within the coral polyp itself without being consumed. In order to determine the presence of red bugs, I use a magnifying glass to look for them before placement into my quarantine system. After that, I observe the coral daily for a week. I also take a photo of each coral and zoom in to look for anything I’ve missed.

How to Treat Red Bug Parasites:

Unlike other serious pests (e.g., Montipora-eating Nudibranchs), there is a suitable in-tank treatment for red bug parasites.

Method 1: Control

Some hobbyists believe that blowing the corals off with a powerhead a few times for a couple weeks will rid the Acropora of red bugs since they may starve before finding their way back to the coral. Other hobbyists rely on natural predation (e.g., pipe fish, file fish, gobies, wrasses), but to my knowledge, no predators have a 100% success rate. I advise against natural control methods for aquarists who plan to sell/trade their corals.

Method 2: Coral Dips

Coral dips often help stun the pests so they can be blown off gently with a pipette or powerhead. Since red bug parasites are live bearers, this method can work as long as all the red bugs are removed. Since a succession of coral dips work for AEFW and red bugs, I dip all Acroporas daily the first week. After that, I dip every other day the second week, every third day the third week, and then once a week for weeks four through six. I have not lost a single coral with this method, and it saves me the hassle of treating with different medications for different parasites at different times.

I should note that I’ve never found a pest after week two, but I still go the full six weeks since the lifecycle of AEFW is quite long (and I always treat for both AEFW and redbugs). Also, some dips can be extremely damaging to smooth-skinned corals, so please use caution if you plan to treat one of these.

Coral Dip Treatment Protocol for Red Bug Parasites:

Follow dip manufacturer instructions.

Method 3: Prescription Flea Medications

Before the manufacturer discontinued it, hobbyists considered Interceptor (milbemycin oxime), a prescription canine flea medication, as the golden standard for red bug parasite treatment. However, as it killed all shrimp, crabs, and other crustaceans, aquarists had to remove them before dosing (the pod population recovered with time). This die-off would also spike ammonia levels, so reefkeepers had to be prepared for a water change and to run carbon. Many people had difficulty obtaining Interceptor from their veterinarians since treating for red bugs is an off-label use. However, the Veterinary Information Network (VIN) published information on red bug parasites for reference.

Once Interceptor was no longer available, reefkeepers began searching for a replacement. Currently, Milbemax is the most often recommended replacement. It is a prescription combination of milbemycin and praziquantel. (The latter medication is commonly used for fluke treatment in reef tanks (e.g., PraziPro); however, it is a much lower dose than would be effective for common marine flukes).

Providing proof of infection to a veterinarian and asking him/her to look up red bugs on the VIN should be enough to receive the medication (or at least it was for us.) Some veterinarians have recommended different medications with different treatment protocol (e.g., MilbeMite Otic), so those individual cases are not discussed here. Unfortunately, many aquarists are finding some red bugs have a resistance to milbemycin. If you try it with no success, work with your veterinarian to find an alternate medication or try one of the other methods listed here.

Interceptor Treatment General Protocol for Red Bug Parasites:

(This is provided for historical purposes only since Interceptor is no longer available, as it may be relevant to other treatments.) Dustin Dorton of ORA determined 0.025 grams of Interceptor are needed per 10 gallons of water. After that, the protocol is the same as Milbemax, described below.

Milbemax Treatment General Protocol for Red Bug Parasites:

(Obtain actual procedures from a veterinarian, as this is for general reference only.) The recommended dosage is 23mg per 400g tank water, which works out to 0.0575mg per gallon tank water (or 5.75mg per 100 gallons if that is an easier reference point). Similar to Interceptor medication, pulverize and weigh the medication out as accurately as possible. Estimate the true volume of water as close as possible (subtracting live rock, sand, etc.)

Remove all crabs, shrimp, and other crustaceans from the aquarium before dosing. Turn down the skimmer so that water runs through it, but the skimmer doesn’t actually skim. Remove GFO and activated carbon. Add an airstone (or multiple, depending on the size of the tank) bubbling gently to help maintain the pH. Otherwise, allow everything else to run so that the chemical can spread throughout the aquarium. Dose the correct amount and let the system run for six hours.

After six hours, the red bugs should be gone, but if they are not, slightly adjust the dosage and try again in a few days. Perform a water change (~15-25%), turn the skimmer back up, and bring the GFO and carbon back online. As mentioned above, although red bugs are live bearers, three treatments a few days apart is still ideal. Once the red bugs are completely eradicated and the medication is removed, reintroduce the crabs, shrimp, and other crustaceans to the aquarium.

Method 4: Bayer Advanced Insecticide

WARNING: Per Bayer Advanced Insecticide’s labeling, “It is a violation of Federal law to use this product in a manner inconsistent with its labeling.”

Yes, this is the stuff you may have in your garage or at your local hardware store. Some aquarists use it as a dip only, not as an in-tank treatment. This website does not cover Bayer use as a coral dip, due to the warning above.

Method 5: Temperature Adjustment

With crazy heat in the summers, lowering the tank temperature may not be feasible. But for tanks located in basements during the winter, this may be the least expensive option. In fact, this method worked for me…accidentally! Right after I received the infested Acropora mentioned above, we lost power for about six hours. My quarantine tank got down to about 65 degrees (thanks to being in Utah in the middle of winter). After the power came back on, there were no signs of red bugs. I’m not the first to document this. I still continued treating for them just in case, but I never saw another one. This seems to work, but we still need scientific studies to back it up.

Experimental Temperature Treatment Protocol for Red Bug Parasites:

Slowly lower temperature to 65-66 degrees. If tank inhabitants start to show signs of stress, start bringing the temperature back up. Leave the temperature at 65-66 degrees for 4-6 hours. Note: this is experimental, and there is not enough data to determine if this treatment works 100% or is safe. Use with caution!

Conclusion: