Machaerotidae are a family of bugs in the superfamily Cercopoidea which were formerly placed within Cercopidae. They are sometimes called tube-forming spittle-bugs as the nymphs form a calcareous tube within which they live. These bugs are mainly found in the Old World tropics. The adults of many genera have a long, free and spine-like process originating from the scutellum and thus superficially similar to the tree-hoppers, Membracidae. The tegmen or forewing, like typical bugs of the suborder Heteroptera, always has a distinct, membranous apical area. Like other cercopoids, these are xylem-sap feeders. The nymph extracts calcium from the xylem fluid and constructs a calcareous tube from Malphigian gland secretions. They typically feed on woody dicots and immerse themselves in a rather clear fluid excretion inside the tube. The tubes strongly resemble the shells of certain serpulid sea worms or helicoid land snails and contain no less than 75% calcium carbonate. This habit is quite uncommon in the class Insecta and markedly different from that of typical spittlebugs, which make and live in a froth mass. Machaerotids produce foam only when they emerge from the tube to moult. There are about 115 species in 31 genera placed in 4 tribes. The majority of species are found in Southeast Asia with a small number in Africa. They were traditionally separated into two subfamilies; Machaerotinae which have the scutellar spine, and Enderleiniinae which lack it. A third subfamily, also lacking the spine, Apomachaerotinae, was recognized in 2014. The scutellum has a "tail" or appears raised towards the posterior end. A list of the subfamilies, tribes and genera is as follows: