When raising larvae in different types of substrate,
You may notice that their frass (droppings) comes in different colors.
By looking at this, you can sometimes make an educated guess about what the substrate is mainly made from.
Larval frass usually resembles the color of the substrate they eat, but it isn’t exactly the same. That’s because after ingestion, gut microorganisms break down woody fibers, and the resulting byproducts mix in.
For substrates that are primarily wood based, the frass color typically ranges from light brown to dark brown.
However, in some cases, the frass can appear almost black.
This is a color that’s hard to see in purely wood-based substrates, and it may indicate that a significant amount of soil organic matter (such as topsoil or humus) has been mixed in.
These kinds of substrates also tend to smell more like earth than dry wood.
The issue is that when using this type of substrate, it can sometimes look like the larvae are producing a lot more frass than they would in a standard wood-based substrate. Because of that, some breeders mistakenly assume, “Lots of poop means they’re growing well.”
In reality, the larvae may simply be eating and excreting more without gaining much weight, because there isn’t much nutrition available in the substrate for them to absorb. which can ultimately lead to slower growth or disappointing adult size.
