Earwigs belong to the insect order Dermaptera. Their most recognizable traits include an elongated body shape and the prominent pair of pincer-like appendages located at the tip of the abdomen.
Overall Dimensions and Appearance
Earwigs exhibit a flattened, elongated body structure. The typical length for an adult earwig ranges from 5 to 25 millimeters (one-quarter to one inch), though some species, like the Australian giant earwig, can reach up to 50 millimeters.
The exoskeleton is relatively smooth and possesses a somewhat shiny texture. Coloration commonly ranges from reddish-brown to dark brown or black. The body is clearly segmented, particularly the flexible and muscular abdomen.
The Defining Feature: Abdominal Pincers
The most distinguishing characteristic is the pair of hard, chitinous, pincer-like appendages, scientifically called cerci. These unsegmented structures function as tools for defense, grasping prey, and folding their complex hindwings. When disturbed, an earwig often raises its abdomen and spreads the cerci as a defensive posture.
The appearance of these pincers differs markedly between males and females, a trait known as sexual dimorphism. Male earwigs possess cerci that are larger, more robust, and noticeably curved or bowed. These exaggerated pincers are often used in ritualistic battles with rival males and during courtship displays.
Female earwigs have cerci that are typically smaller, straighter, and held more parallel, giving them a scissor-like or forceps-like appearance. This difference in pincer shape provides a reliable way to determine the sex of the insect. The female’s straighter pincers are thought to be more efficient for tasks like defending their eggs.
Head Structure, Antennae, and Wings
Head Structure and Antennae
The earwig’s head is small and positioned facing forward, a configuration known as prognathous. It features simple, chewing mouthparts adapted for their omnivorous diet of plants and small insects. The head bears a pair of compound eyes, though many species lack simple eyes (ocelli).
A pair of long, slender antennae extends from the front of the head. These antennae are thread-like (filiform) and are composed of many small segments, often numbering ten or more. Earwigs use these segmented antennae for chemo-sensation, helping them navigate their environment and locate food or mates.
Wings
The majority of species possess two pairs of wings. The forewings are short, leathery, and veinless structures called tegmina, which act as protective covers for the delicate hindwings underneath. The scientific name for the order, Dermaptera, literally means “skin wings,” referencing these protective forewings.
The hindwings are large, membranous, and semicircular, featuring veins that radiate outward. When not in use, these hindwings are folded intricately, multiple times beneath the tegmina, making them largely invisible. Most earwigs rarely take to the air, preferring to use their wings only when necessary for dispersal.