Mollicutes are parasites of various animals and plants, living on or in the host's cells. Many cause diseases in humans. "Mycoplasma" and "Ureaplasma" stick to cells in the lungs or sex tubes like the urethra. "Phytoplasma" and "Spiroplasma" are plant pathogens with insect vectors. Bugs such as leaf-hoppers (Homoptera) are the vectors. They deliver the parasites which they stick their mouth-parts into a plant to suck its sap.