Most cockroaches live in tropical regions. Less than one percent of them are pests, adapted to human habitats, thriving in warm, unsanitary conditions, and often carrying disease. Cockroaches mostly eat organic matter, including bird and bat guano. Their main defense against predators is that they are highly sensitive to vibration and can run fast, but some also spray or ooze toxic chemicals.
 

The wood roaches are the most primitive cockroaches and belong to a single genus: Cryptocercus. They are quite elongate and are shiny darb brown to black.
 

Wood roaches live in small family groups compromising two adults and 20 nymphs. They tunnel through dead wood--sticking their eggs to the roof of the wooden chambers--and use special symbiotic protozoans in their gut to break down the wood and cellulose into sugars. Each time nymphs molt, they eat some of the group's droppings, thus reinfecting themselves with the protozoans.
 

North America and China. In dead wood in a variety of habitats.