Some parasitic forms affect humans and other mammals, causing damage by their feeding, and can even be vectors of diseases such as scrub typhus and rickettsia. A well-known effect of mites on humans is as an allergen which stimulates asthma. Predatory mites may be used in pest control and herbivorous mites used to attack weeds. A positive contribution of the Acari is their normal functioning in ecosystems, especially their roles in the decomposer subsystem.