The Unseen Influence

on the back of a cockroach no larger than myself millions of influenza germs may lodge i have a sense of responsibility to the public and i have been lying for two weeks in a barrel of moth balls in a drug store without food or water

—archy, "quarantined"

Why are cockroaches almost universally loathed? One of the primary reasons is because of the habitats they frequent in the human environment. Cockroaches are associated with sewers, cesspools, latrines, septic tanks, garbage cans, chicken houses, animal cages, and anywhere else there are biological waste products. Their attraction to human and animal feces, rotting food, secretions from corpses, sputum, pus, and the like gives them a well earned "disgust factor" among the general public (Roth and Willis, 1957). Why, however, are they are attracted to environments reviled by most other animals? It is it is obvious to us that the common denominator in all these moist, organic habitats is the staggeringly dominant presence of bacteria, protozoa, amoebae, fungi, and other microbial material. While these consortia are rarely if ever discussed as food for macroarthropods (e.g., Coll and Guershon 2002), in the case of cockroaches, that may be a glaring oversight. The main source of nourishment for cockroaches in mines and sewers, for example, is human feces (see Roth and Willis, 1957, plate 4), which can be 80% bacterial, by fresh weight (Draser and Barrow, 1985). Blattella germanica has been observed feeding on mouth secretions of corpses riddled with lung disease; these secretions contained infectious bacteria in almost pure culture (Roth and Willis, 1957). Granted, the above cases refer to cockroaches associated with the man-made environment, while the main focus of this book is on the 99%+ species that live in the wild. We contend, however, that microbes are an essential influence in the nutrition, ecology, and evolution of all cockroaches; indeed, it can be difficult to determine the organismal boundaries between them. Here we address microbes as gut and fat body mutualists, as part of the external rumen, the food value of microbes, various mechanisms by which cockroaches may ingest them, and some non-nutritional microbial influences. Finally, we discuss some strategies used by cockroaches to evade and manage disease in their microbe-saturated habitats.

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