Wingless

Wingless is an adjective used in biology to describe organisms that lack wings or any winglike structures. It can refer to individuals, life stages, or entire lineages. In scientific terminology, the condition is often described as apterous, with apterous insects being those that never develop wings. Related terms include brachypterous for individuals with shortened wings and vestigial for wings that persist but are nonfunctional.

Winglessness arises through evolutionary adaptation, developmental processes, or environmental pressures. Some species are permanently wingless, while others display winged and wingless morphs depending on age, sex, or ecological conditions. In many insects, wingless forms are common in social castes or in parasitic or sedentary lifestyles, where wings provide no selective advantage.

Examples include various wingless insects such as many lice and fleas, and several termite and ant workers that never develop wings. Aphids can alternate between winged and wingless morphs in response to host quality and population density. Among vertebrates, some birds are flightless or have greatly reduced wings, such as ostriches, emus, cassowaries, kiwis, and penguins. In these species, wings are commonly used for balance, stabilization, or swimming rather than powered flight.

Ecologically, winglessness can reduce energy expenditure on wing development and maintenance and may facilitate life on the ground or in stable environments. However, it can limit dispersal and colonization of new habitats, making wingless populations more prone to geographic isolation.