Aculeus

Definition

A slender, sharply pointed cuticular process, typically referring to the modified ovipositor of aculeate Hymenoptera (stinging wasps, bees, and ants) that functions as a venom-injecting stinger, or to the post-anal stinger of scorpions. In insects, the aculeus is derived from the gonapophyses of abdominal segments 8–9 and is often associated with a venom gland and reservoir; it may be used for defense, prey subduing, or host manipulation. The term distinguishes this piercing structure from the unmodified, egg-laying ovipositor of parasitoid wasps.

Etymology

Latin aculeus, diminutive of acus 'needle'

Example

In honey bees (Apis mellifera), the aculeus is barbed and remains embedded in vertebrate skin after stinging, resulting in evisceration of the stinger apparatus and death of the worker; in paper wasps (Polistes), the smooth, unbarbed aculeus permits repeated stinging without self-injury.

Synonyms

• stinger
• sting apparatus

Related Terms

• ovipositor
• gonapophysis
• Aculeate
• Telson
• venom gland
• Dufour's gland

Usage Notes

The term is most precisely applied to Hymenoptera (where it defines the clade Aculeata) and Scorpiones; some authors extend it to other sharp integumentary projections, but this usage is less common in entomology. Contrast with 'stylus' or 'stylet' in other insect groups. In scorpions, the aculeus is the curved terminal segment of the telson, not a modified ovipositor.