Isopods, commonly known as pill bugs or roly-polies, are small terrestrial crustaceans that function as decomposers. They serve a function in ecosystems by breaking down organic matter that would otherwise accumulate. Isopods consume feces, a behavior known as coprophagy, which is a necessary part of their feeding strategy. This practice helps them extract nutrition from their low-quality diet.
The Specifics of Coprophagy
Coprophagy is a specialized feeding behavior, allowing isopods to recapture nutrients not absorbed during the initial passage of food. Isopods regularly engage in autocoprophagy, meaning they consume their own feces. The feces are rich in digestive microbes and undigested plant material, making them an immediate, recycled food source.
When an isopod digests plant detritus, it cannot extract all the nutrition in a single gut passage. The waste product quickly becomes colonized by bacteria and fungi, which break down the remaining complex fibers. By consuming this microbe-enriched waste, the isopod gains access to newly synthesized microbial cells, which are more nutrient-dense than the original leaf matter. This recycling optimizes nutrient uptake when the primary diet is of low quality.
Beyond Waste: The Role of Detritivory
While coprophagy is a specialized strategy, the isopod’s primary diet involves consuming decaying organic material, classifying them as detritivores. Their preferred food sources are decaying leaf litter, soft rotten wood, and other dead plant tissues. This decaying matter, known as detritus, is composed largely of compounds like cellulose, hemicellulose, and lignin.
Breaking down these tough plant cell wall components is difficult for most organisms. Isopods manage this challenge using a combination of their own digestive enzymes and symbiotic gut microflora. The digestive system breaks down the material mechanically and chemically, but the gut microbiota assists in the digestion of these complex polymers. This cooperative breakdown ensures the isopod can utilize a globally abundant food source that is nutritionally inaccessible to many other animals.
Essential Nutrient Recycling
The nutritional challenge of a detritus-based diet explains the necessity of their feeding behaviors. The gut microflora, housed in the digestive midgut glands, provides the host with essential nutrients beyond breaking down tough fibers. The isopod digests the microbial cells themselves, acquiring lipids, B vitamins, and other compounds synthesized by the bacteria.
This recycling process is also connected to mineral balance, particularly copper. Isopods use copper-based hemocyanin to transport oxygen, but they are inefficient at extracting this metal from low-copper diets in one cycle. When feeding on natural leaf litter, they can lose more copper through their feces than they ingest. Re-ingestion of their waste is a mechanism to ensure they maintain a positive copper balance. Coprophagy maximizes the extraction of microbial-produced vitamins and essential trace minerals needed for survival and growth.