Dung beetles and dung flies are mainly attracted to herbivore (mostly mammal) dung ,and their plant meals take a lot of digesting.
Cellulose, the major constituent of plant mass, is made up of long chains of sugar-like molecules, much in the same way that plastics are polymers made up of short repeating units. Cutting up these unwieldy compounds into readily digestible and absorbable nutrients is slow and cumbersome, so herbivores recruit micro-organisms to help.
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Gut flora – a complex of micro-organisms that live in animal digestive tracts – contains more bacteria than the rest of the animal itself has cells. In order to get enough out of cellulose-rich but protein-poor grass and leaves, horses, cows and sheep (for example) consume vast amounts of food and rely on a high-turnover, bucket fermentation-type of digestion in which the bacteria assist.
When voided, dung is a combination of still-working bacteria, cellulose fragments and only partially digested plant pieces. It is not surprising that much valuable material passes through the intestinal tract to be used on the other side. Dung is, after all, just pre-owned food.
