Most cockroaches feed on decaying organic matter, which traps a lot of nitrogen," Kambhampati said. "Cockroach feeding has the effect of releasing that nitrogen (in their feces) which then gets into the soil and is used by plants. In other words, extinction of cockroaches would have a big impact on forest health and therefore indirectly on all the species that live there.

via livescience

so cockroaches are not as useless as i thought and neither is their poop… WTF