What do millipedes primarily feed on?

Millipedes primarily feed on decomposing plants, which is integral to their role in the ecosystem. As detritivores, they play a crucial part in breaking down organic matter, such as dead leaves and decaying plant material. This process contributes to soil health and nutrient cycling by returning essential nutrients back into the soil, helping to support the growth of new plants.

The other options involve organisms or materials that do not form a part of their natural diet. Living insects would be a predatory diet, which is not characteristic of millipedes. Small mammals and human skin are not suitable food sources for millipedes either, as they do not have the feeding mechanisms to consume such materials. This distinguishes millipedes as important decomposers rather than predators or scavengers of larger organisms.