Earwigs, members of the insect order Dermaptera, are common garden and household pests recognized by the distinctive pair of pincer-like appendages, or cerci, extending from their abdomen. Though generally harmless, they possess a peculiar defense mechanism. When physically threatened or disturbed, the earwig secretes a malodorous, yellowish-brown liquid. This defensive behavior is the source of the noticeable and often unpleasant smell associated with the insect.
Describing the Defensive Scent
The odor released by a threatened earwig is consistently described as foul and objectionable, though its exact character can vary slightly between species. Many people perceive the scent as strongly acrid or chemical, sometimes comparing it to the smell of a spent battery or the additive used to scent natural gas. The secretion is visibly deployed by the insect when it feels sufficiently agitated.
Other descriptions liken the smell to a pungent, musty quality, or a slightly oily and metallic odor in more concentrated instances. The odor is easily noticed upon direct handling or crushing the insect, but it is not overpowering in open air. The intensity depends on the proximity to the source and the concentration of the released substance. The brief duration of the odor suggests the volatile nature of the compounds responsible for the sensory experience.
The Biological Mechanism Behind the Odor
The source of the earwig’s smell is a pair of specialized defensive glands located on the dorsal side of the abdomen, typically opening near the third and fourth segments. These glands produce a secretion that is a complex mixture of volatile organic compounds. The characteristic acrid or chemical smell is primarily caused by the presence of quinones.
Specific compounds identified include 2-methyl-1,4-benzoquinone and 2-ethyl-1,4-benzoquinone. Quinones are known irritants and are responsible for the sharp, chemical notes of the odor. The secretion also contains hydrocarbon solvents, such as pentadecane, which help dissolve the quinones and facilitate the spray mechanism. This mixture of irritating chemicals is discharged through minute openings, often as a directed spray, functioning as a highly specific chemical defense.
Why Earwigs Release the Smell
The primary function of the odorous secretion is chemical defense against potential predators. Earwigs deploy the liquid when startled, physically seized, or crushed, using it as a deterrent. The unpleasant smell and irritating nature of the quinones strongly discourage creatures like ants, spiders, and small vertebrates that might prey on the insect.
In addition to its repellent function, the secretion also serves a broader purpose. Research shows that the quinones possess antimicrobial, antifungal, and nematicidal properties. This suggests the chemical defense is multifunctional, not only deterring predators but also helping the earwig sanitize its microenvironment in damp, soil-based habitats. The insect often aims the discharge by rapidly revolving its abdomen, maximizing the impact of the defensive jet.
Handling Earwig Encounters
If an earwig releases its defensive secretion, the odor is typically short-lived because the quinone compounds are highly volatile and dissipate quickly. The liquid itself is irritating but is not known to be toxic to humans or pets in the small amounts deployed. A physical encounter, such as accidentally crushing the insect, is required to release a noticeable amount of the odor.
To clean any surfaces where the liquid was deployed, simple household soap and water will suffice to remove the residue. Adequate ventilation will hasten the breakdown and disappearance of the volatile odor molecules. Since the earwig’s defense is primarily a deterrent, the best course of action is to avoid handling the insect directly, allowing it to move away naturally.