Brazilian Treehopper

Bocydium globulare — the Brazilian treehopper — is one of the most morphologically extraordinary insects on Earth and the textbook iconic species of family Membracidae (the treehoppers, ~3,000 species worldwide). The defining feature is a dramatically modified pronotum (the dorsal plate of the thorax) that has evolved into three pairs of stalked black globular structures arranged in a crown over the head, plus a long tapered posterior projection. The structures are hollow and lightweight; their function has been the subject of decades of evolutionary biology speculation but is not definitively resolved. Leading hypotheses include: (1) predator deterrence — the structures resemble fungal galls, parasitoid pupae, or ant mimicry warnings, and visually-hunting predators may avoid them; (2) intra-specific recognition — males and females may use the structures to identify each other species; (3) vibration communication — the hollow structures may amplify or transmit substrate-borne vibrations used in courtship; (4) sexual selection by mate choice. Family Membracidae as a whole shows extraordinary variation in pronotal extensions across species: some look like horns, some like leaves, some like ant-mimics, some like spiny seeds. Membracid biology is otherwise typical of true bugs (Hemiptera): they feed on plant phloem with stylet mouthparts, are tended by ants for honeydew (in many species), and have nymphal stages with their own bizarre ornaments. The Brazilian treehopper is one of the most-photographed insects in modern macro nature photography because of the alien appearance.