Earwigs belong to the insect order Dermaptera and are common inhabitants of many global ecosystems. Their most distinctive feature is a pair of prominent, forceps-like appendages called cerci located at the end of their abdomen. Despite their somewhat intimidating appearance, these insects are largely harmless to humans. The story of the earwig’s presence in various parts of the world involves ancient evolutionary history and recent human-aided migration.
Defining the Earwig
The order Dermaptera comprises approximately 2,000 known species globally, making it one of the smaller insect orders. Earwigs have an elongated, somewhat flattened body that typically exhibits colors ranging from yellowish-brown to dark reddish-brown. Their scientific name, Dermaptera, translates to “skin wings,” referring to their forewings, which are short, thick, and leathery protective covers. Beneath these covers are large, semicircular hindwings that fold intricately like a fan beneath the forewings when at rest.
The characteristic cerci are unsegmented and heavily sclerotized, varying in shape between sexes, generally being more curved in males. These pincers serve multiple functions, including defense, capturing prey, and assisting in the complex process of folding their large hindwings. Earwigs are primarily nocturnal and omnivorous, feeding on a diverse diet that includes decaying organic matter, plants, and small arthropods. Female earwigs display an uncommon trait among insects: maternal care, where they guard their eggs and newly hatched young in underground nests.
Global Origins and Primary Native Ranges
The evolutionary history of earwigs suggests their origins are rooted in the ancient supercontinent Gondwana, placing their highest natural diversity in the tropical regions of the Southern Hemisphere. This Gondwanan lineage means that the most species-rich areas today are concentrated in tropical zones. The colonization of the Northern Hemisphere was historically limited by climatic factors and geographic barriers. Colder temperatures and major geological events, such as the rise of the Himalayan mountain range, hampered their natural dispersal into the Palearctic region.
The species most familiar to people in temperate zones, the European earwig (Forficula auricularia), is natively distributed across the Old World, specifically Europe, Western Asia, and Northern Africa. Numerous other species are endemic to specific Old World regions, often found in tropical islands or remote mountain ranges. This pattern highlights that the vast majority of earwig species are naturally confined to the Eastern Hemisphere and the tropics.
Mechanisms of Worldwide Expansion
While many earwig species remain within their native ranges, a few, notably the European earwig, have achieved a nearly cosmopolitan distribution through human activity. This global expansion began with the rise of international trade and shipping in the late 19th and early 20th centuries. The European earwig was first observed in North America in Seattle, Washington, around 1907, and quickly spread across the continent. This rapid movement occurred by hitchhiking in human cargo, not by their own limited locomotion.
Earwigs thrive in dark, moist environments, making them adept at hiding in crevices within transported goods. They are frequently intercepted in shipments of produce, nursery stock, potted plants, and other products that offer damp shelter. The movement of soil, lumber, and personal items has facilitated their transport across oceans and continents. This human-assisted dispersal has allowed them to establish introduced populations in regions like North America, Australia, New Zealand, and parts of South America, where they are now considered non-native species.
Environmental Factors Shaping Distribution
The survival and local distribution of earwigs are dictated by specific ecological requirements. Earwigs have a strong preference for warm and humid climates and are particularly susceptible to desiccation. They require consistent moisture and are often found hiding in dark, damp microhabitats during the day, such as under stones, in dense leaf litter, or beneath bark. This need for humidity is a primary constraint on their range.
The European earwig, despite its adaptability, does not naturally thrive in extremely arid environments or areas with severe, prolonged cold. In drier regions, their survival is often dependent on human-managed water sources, such as irrigated agricultural fields or gardens. Studies have shown a positive correlation between precipitation levels and earwig species richness. Their inability to withstand prolonged dry or freezing conditions remains the primary biological barrier to their global conquest.
Conclusion
Earwigs are a diverse insect order with deep evolutionary roots in the Old World and the tropical Southern Hemisphere. Their highest natural species richness is found in warm, humid tropical zones, consistent with their Gondwanan origin. Widespread species, such as the European earwig, achieved global distribution in temperate areas recently due to human commerce. Their current presence in non-native territories requires consistent humidity and moderate temperatures.