Aculeus

This term has several meanings depending on the taxon of insects under consideration. In Hymenoptera, it is synonymous with the sting, an eversible hollow cylindrical structure at the tip of the abdomen used to deliver venom. Though derived from the ovipositor, it is not used to deliver eggs.

Among Diptera, this term is sometimes used to refer to a pointed, sclerotized structure associated with the reproductive system in males. Among Lepidoptera, this term refers to hair-like structures on the body and wings of primitive moths; these also are known as microtrichia.