Black bugs

Identification

Very tiny dark copepod-like specks, smaller than red bugs and not visible to the naked eye — a hand lens shows only a speck, and the black body with a small red spot is only clear under a dissecting microscope. In the tank the signs are indirect: Acropora losing color, reduced polyp extension and decline starting from the bottom, sometimes at densities around 20 bugs per inch of heavily affected coral. A dip of a suspect frag, watched closely, often reveals bugs emerging from the polyps.

Often confused with

Red bugs — red bugs are larger (about 0.5 mm), yellow-gold with a red dot or rear, and crawl visibly on tissue in macro photos; black bugs are smaller, predominantly black, and need a microscope to confirm. Also confused with AEFW (flat gliding worms, far larger) and with a separate flatworm-type pest that some forums also call black bugs — a mobile navy-blue slug around 3–4 mm that preys on hard corals, which is a different animal entirely.

What it targets

Reported chiefly on Acropora in the SPS hobby, with the same common name also applied by keepers to copepods hitting Montipora and, in some threads, LPS such as torches. They burrow into and irritate polyps, driving retraction and slow decline from the base up.

How it spreads

Hitchhikes on Acropora frags moving between hobbyists and shops; the Canreef outbreak report found them on multiple recent frag purchases from different sellers in one area. Because they are effectively invisible without magnification, they spread through ordinary frag trading before anyone knows they are present.

Control (safest first)

Confirm the ID under magnification before treating: several unrelated pests share the black bug name, and treatment aimed at the wrong animal wastes months. Photograph through a microscope or dissecting scope and compare against red bug references. Bayer-type dips on removable frags: the Canreef reporter found CoralRx-type dips ineffective on these copepods while a Bayer dip worked. Basting during the dip matters because these bugs burrow into polyps and cling on. Repeat dips plus quarantine for encrusted systems is incomplete by itself — a Reef2Reef keeper with encrusted Acropora could not dip everything and looked to whole-tank treatment for that reason. In-tank milbemycin oxime products (Interceptor from a veterinarian, or Dr. G's SPS/LPS dip dosed in-tank per its maker and keeper reports): black bugs are repeatedly described as more resilient than red bugs and needing the higher end of reported dosing; the Reef2Reef Dr. G's thread discusses trial dosing around 1 ml per 2 gallons on a test colony before committing the display. NOT selective — milbemycin kills shrimp, crabs and pods, so remove ornamental crustaceans first and be ready for a large water change and carbon afterward. This is prescription / off-label territory; follow a veterinarian's or manufacturer's directions rather than forum numbers alone. Predator backstop: melanurus and six-line wrasses and dragonets are kept by several affected hobbyists and may suppress numbers, but keepers who relied on a wrasse alone still carried the pest — do not count on fish for eradication.

Natural predators

• Melanurus wrasse→
• Six-line wrasse→
• Dragonface pipefish

Field notes

A Canreef keeper traced black bugs to recent Acropora frags from several local sellers, describing a copepod smaller than red bugs, black with a red spot, invisible to the naked eye and barely a speck under a hand lens; CoralRx dips failed, a Bayer dip worked, and heavily hit corals carried roughly 20 bugs per inch with decline starting at the base. A Reef2Reef keeper treating with Dr. G's reported the bugs seemed to prefer Montipora yet still infested Acropora, burrowed into polyps so dips alone missed them, and a Revive dip of a small frag shook loose hundreds of animals — illustrating both the burrowing habit and how heavy loads can be on a single frag. An INDMAS keeper learned the name the hard way in a Montipora-heavy tank, describing tiny black specks, corals fading to an anemic look rather than bleaching, and choosing an in-tank milbemycin product because encrusted colonies could not be removed for dipping — a reminder that under this one common name, keepers report Acropora, Montipora and even LPS being hit.