What is Stachybotrys?

The organism behind the nickname

Stachybotrys is a group of molds that live naturally in soil and on decaying plant matter such as straw, hay and wood. Several species exist, but indoors the one that comes up most is Stachybotrys chartarum. Researchers have also described a very similar species, Stachybotrys chlorohalonata, that can only be told apart reliably in a lab, so reports sometimes group them together.

The popular name black mold isn’t a scientific term, and plenty of other molds are black. What sets Stachybotrys apart isn’t its color but its growing needs, which make it a fairly specific signal about a building’s water history.

What it needs to grow

Stachybotrys is a slow grower that needs a lot of moisture for a long time. Short spills and occasional condensation usually favor faster molds, which colonize a surface first. Stachybotrys tends to show up where material has been soaked for weeks, or wet over and over, and where that material is rich in cellulose. Paper, cardboard, wallboard facing and some wood products suit it well.

Where it’s often found	Why
Back of drywall inside wall cavities	Paper facing stays wet after a hidden leak
Ceiling tile and drywall under roof or plumbing leaks	Repeated wetting of cellulose
Basements after flooding	Wallboard and stored cardboard soaked for long periods
Under sinks and behind appliances	Slow drips that go unnoticed
Wet cardboard boxes and paper in storage	Pure cellulose in a damp spot

What it looks like, and why looks aren’t enough

Active Stachybotrys growth is typically dark green to black and can look wet or slimy. As it dries it can turn sooty or powdery. It often appears in patches with other molds around it, and on the back of drywall it may be far more extensive than anything visible from the room side.

You can’t confirm it by eye. Under a microscope, a tape lift or bulk sample shows its distinctive spore-bearing structures, which is how a lab identifies it. Its spores are sticky and tend to clump rather than float, so air samples can miss it even when it’s growing in a wall. Dust DNA methods such as HERTSMI-2 testing and ERMI include Stachybotrys chartarum, which helps show whether it has been growing somewhere in the home.

Stachybotrys and mycotoxins

Some strains of Stachybotrys chartarum produce macrocyclic trichothecenes, and others produce a different group of compounds instead. The mold being present doesn’t tell you which kind you have. Our page on trichothecenes and Stachybotrys covers the toxins and how they’re tested, and black mold vs. mycotoxins explains why color is a poor guide.

What finding it means for a cleanup

• There’s almost certainly a moisture problem that has lasted a while. Finding it is step one.
• Growth on the room side often means more inside the cavity, so investigation usually goes behind the surface.
• Affected drywall, ceiling tile and cardboard are generally removed under containment rather than cleaned.
• Don’t scrape, sand or dry-brush it yourself. That’s how fragments get spread through the house.
• Dust testing after the work shows whether the rest of the home was affected and whether cleanup succeeded.

We identify and remove mold and mycotoxins in buildings. We don’t diagnose or treat medical conditions, and nothing on this page is medical advice. If you’re concerned about exposure, please talk with a doctor. With your permission, we’ll share our findings with them.