Cercus

A common earwig with large cerci in the background.

Cerci (singular cercus) are paired appendages on the rear-most segments of many arthropods, including insects and arachnids but not crustaceans. Cerci often serve as sensory organs, but they may also be used as weapons, copulation aids, or vestigial structures.

Typical cerci may appear to be jointed and hair-like, but they can take very different forms. Earwigs and some diplurans have large, stout pincer-like cerci. crickets have particularly long cerci while other insects have cerci that are too small to be noticeable. Some insects have an acompanying third tail filament which extends from the tip of the abdomen. Aphids have tube-like cornicles or siphunculi that are sometimes mistaken for cerci.

References

• Kendall Bio-Research Services
• University of Sydney Biology Dept