Treehopper

  Treehoppers and thorn bugs are members of the family Membracidae, a group of insects related to the cicadas and the leafhoppers. There are about 3000 species of treehoppers, in over 600 genera. They are found on all continents, although there are only three species in Europe. They are best known for their enlarged and ornate pronotum, which most often resembles thorns, apparently to aid camouflage. They pierce plant stems with their beaks, and feed upon sap. Excess sap becomes concentrated as honeydew, which often attracts ants. Some species have a well developed ant mutualism, and these species are normally gregarious as well, which attracts more ants. The ants provide protection from predators. Eggs are laid in slits cut into the cambium or live tissue of stems, by the female with her saw-like ovipositor, though some species lay eggs on top of leaves or stems. The eggs may be parasitised by wasps, such as those of Mymaridae and Trichogrammatidae. The females of some membracid species sit over their eggs to protect them from predators and parasites, and may buzz their wings at the intruder. The females of some gregarious species work together to protect each others' eggs. In at least one species, Publilia modesta, mothers serve to attract ants when nymphs are too small to produce much honeydew.

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Like the adults, the nymphs also feed upon sap, and unlike adults, have an extensible anal tube that appears designed to deposit honeydew away from their body. The tube appears to be longer in solitary species that are rarely ant attended. It is important for sap feeding bugs to dispose of honeydew, as otherwise it can become infected with sooty mould. Indeed, there is evidence that one of the benefits of ants for individuals of the species Publilia concava is that ants remove the honeydew and reduce such growth.

  Most species are innocuous to humans, although a few are considered minor pests, such as Umbonia crassicornis (a thorn bug), Spissistilus festinus (Three-cornered Alfalfa Hopper) and Stictocephala bisonia (Buffalo Treehopper).

Trivia

• Thorn bugs are one of the types of insects mentioned in the movie Master and Commander: The Far Side of the World.