What Stachybotrys (“Black Mold”) Actually Looks Like and How to Confirm It

If you’ve ever found a dark patch on drywall or behind a sink and felt a chill run down your spine, you’re not alone. “Black mold” has reached near-mythical status in homeownership, often conjuring images of toxic spores hiding behind every wall. The truth is more grounded—but still important to understand. Stachybotrys chartarum, the mold most people mean when they say “black mold,” has a very specific appearance and only grows under very specific conditions. Once you know what to look for, it becomes much easier to tell whether the suspicious spot in your home fits the profile.

Stachybotrys almost always appears dark green to black, but what sets it apart is its texture. When it’s actively growing and still wet, it looks slimy or wet-sponge-like—almost shiny, as if the surface is coated in a thin layer of oil. As it dries, the colony becomes more matte and powdery, but never fuzzy or cloud-like the way Penicillium or Aspergillus often appear. Stachybotrys attaches firmly to the surface beneath it, and scraping it off isn’t easy; it embeds itself deep into the material because of the way its hyphae grow through cellulose.

That word—cellulose—is part of the secret. Stachybotrys doesn’t grow just anywhere. It needs constant moisture for long stretches of time, sometimes weeks or months, and it prefers building materials like drywall, paper backing, insulation, particleboard, or carpet underlayment. This is why true Stachybotrys often signals hidden water damage rather than everyday humidity. If you see a dark patch that appeared quickly on a relatively dry surface, it’s likely something else.

Another hallmark is its pattern. Stachybotrys tends to develop in dense, circular patches or thick, irregular spreads that lack the concentric rings you see in other molds. It often shows up at the base of walls, behind cabinets, near plumbing leaks, under sinks, beneath flooring, or anywhere significant water intrusion has occurred. If your home recently had a roof leak, flooding, or a persistent plumbing issue, the setting is right for Stachybotrys—and that’s when visual inspection truly matters.

But here’s the challenge: many molds look dark, and photos online often blur the distinctions. Even experienced inspectors won’t confirm Stachybotrys by sight alone. The only reliable way to know the species is through testing, because several molds—including Ulocladium and Cladosporium—can mimic its color but not its underlying behavior.

If you want to confirm whether a patch may be Stachybotrys, a targeted surface sample is the safest approach. The Detekt Home Mold Test Kit allows you to collect a sample from the exact spot you’re concerned about so the lab can determine whether the growth matches Stachybotrys or another mold species associated with moisture or humidity. This clarity helps you decide whether simple cleaning is enough or whether professional remediation is necessary.

The important takeaway is this: Stachybotrys doesn’t hide everywhere—it grows only when a home gives it the one thing it loves most: constant, prolonged moisture. If you know what to look for, and you confirm your findings with proper testing, you can respond appropriately and confidently without the fear-driven guesswork that “black mold” often inspires.

By A. Anagnos, Biomedical Engineering Specialist