The earwig produces a distinct and unpleasant odor when it is threatened or crushed. This phenomenon is a direct result of its biological defense mechanism. When the earwig is disturbed, especially by mechanical action, it releases a foul-smelling liquid from specialized glands on its abdomen. This smell is not a sign of decomposition but rather a chemical deterrent designed to repel predators.
The Chemical Origin of the Earwig’s Scent
The source of the earwig’s noxious odor is a defensive secretion produced by paired sac-like glands located in the third and fourth abdominal segments. In many species, these glands are identified as pygidial glands, which manufacture the deterrent liquid. The secretion itself is a complex mixture of chemical compounds, with the most potent odor components being short-chain quinones.
Specific compounds identified in the defensive exudate of the European earwig include 2-methyl-1,4-benzoquinone and 2-ethyl-1,4-benzoquinone. These chemicals are highly volatile, which allows the scent to rapidly disperse into the air upon release. The quinones are often combined with other substances, such as alkanes, which serve as a carrier for the active ingredients.
When the insect is physically crushed, the integrity of these abdominal glands is compromised, causing an immediate and concentrated release of the stored quinone solution. The earwig can also actively discharge the secretion as a spray when disturbed, aiming the jet by revolving its abdomen. This active deployment, or the passive release upon crushing, creates the noticeable, pungent smell experienced by humans due to the volatile quinones reacting with the air.
The Purpose and Characteristics of the Odor
The primary function of this malodorous secretion is chemical defense against predators. The repulsive odor acts as a fast-acting deterrent to creatures like ants, birds, and small mammals. The ability to spray the foul-smelling liquid for distances up to four inches enhances the effectiveness of this defensive strategy.
To a human nose, the scent of the defensive secretion is described as acrid, musty, or intensely pungent. Some people liken the smell to stale vinegar, ammonia, or a metallic, battery-like odor due to the presence of the quinones. The strong, objectionable nature of the scent makes it an effective deterrent, causing a predator to drop or reject the earwig.
Beyond deterring predators, the defensive secretions possess a secondary role. Analysis has shown that the quinone-based exudates also exhibit antimicrobial activity. This suggests the chemicals help the earwig, which lives in moist soil, to combat bacteria, fungi, and nematodes in its microenvironment. The smell is a byproduct of a dual-purpose chemical system for both external defense and internal sanitation.
Safety and Toxicity of Earwig Secretions
Despite the foul smell and the chemical nature of the secretion, the defensive liquid is considered non-toxic to humans and household pets. The odor is noxious and unpleasant, but the small quantity of quinones released is insufficient to cause serious poisoning. The belief that earwigs are poisonous often stems from this foul-smelling liquid.
The main effect of contact with the secretion is annoyance due to the odor. Direct contact with the liquid may cause minor, temporary irritation, but the chemicals are not corrosive or venomous. Earwigs lack the biological structures for venom delivery, such as stingers or fangs, relying solely on the repulsive nature of the scent for defense.
If an earwig is crushed on the skin, cleaning the area with soap and water is sufficient to remove the chemical residue and the offensive smell. The insect’s pincers, or cerci, can deliver a slight pinch if handled roughly, but this action is harmless. The chemical defense is a nuisance, not a health hazard, meaning the primary risk posed by the earwig is to garden plants rather than to people or pets.