Cercus

Cerci (sg.: cercus) are paired

In basal arthropods, such as silverfish, the cerci originate from the eleventh abdominal segment. As segment eleven is reduced or absent in the majority of arthropods, in such cases, the cerci emerge from the tenth abdominal segment.^[2] It is not clear that other structures so named are homologous. In the Symphyla they are associated with spinnerets.^[1]

Morphology and functions

Most cerci are segmented and jointed, or filiform (threadlike), but some take very different forms. Some Diplura, in particular Japyx species, have large, stout forcipate (pincer-like) cerci that they use in capturing their prey.^[3]

The

Crickets have particularly long cerci while other insects have cerci that are too small to be noticeable. However, it is not always obvious that small cerci are without function; they are rich in sensory cells and may be of importance in guiding copulation and oviposition.

In groups such as crickets and cockroaches, cerci play important sensory roles. They have been shown to be sensitive to puffs of air and low-frequency vibration, and thus trigger anti-predatory responses such as escape in response to certain predators. In field crickets, the range of frequency detection by the cerci spans from infrasonic sound to nearly 1 kHz. It is worth noting that in crickets, higher-frequency sound such as stridulation and ultrasonic bat calls are picked up by a separate tympanal organ, not the cerci.^[4]

Some

Aphids have tube-like cornicles or siphunculi that are sometimes mistaken for cerci but are not morphologically related to cerci.

Evolutionary origin

Like many insect body parts, including

• 
  Short cerci on abdomen of a species of Pamphagid grasshopper
• 
  Long sensory cerci on Ctenolepisma, flanking the median cerciform appendage and paired stylets
• 
  Two forms of Diplura, illustrating cerci with sensory glandular function, as contrasted with forcipate forms of cerci used in predation

References