Do worms have hair? This common question comes from observing small, bristle-like structures on their bodies. While these structures visually resemble hair, worms do not possess true hair in the biological sense. True hair is a unique characteristic of mammals, serving functions like insulation and sensory perception. The structures on worms are distinct in composition, origin, and purpose.
What Worms Possess
Worms, particularly earthworms, possess specialized anatomical features called setae, also known as bristles. These stiff, hair-like projections are integral to their movement and interaction with their environment. Setae are primarily composed of chitin, a tough, flexible polysaccharide that also forms the exoskeletons of insects and crustaceans.
These structures are S-shaped and are embedded within an epidermal pit on the worm’s body segments. Earthworms have eight setae per segment, arranged in four pairs. Setae are absent from the first, last, and clitellar segments of the worm’s body.
The Function of Bristles
The primary function of these chitinous bristles is to facilitate locomotion and provide traction. Earthworms move through a wave-like muscular contraction and relaxation process called peristalsis. During this movement, the setae extend to grip the surrounding soil or substrate, preventing the worm from slipping backward.
As some segments shorten and thicken, anchored by their bristles, other segments lengthen and thin, pushing the worm forward. This coordinated action of muscles and setae allows the worm to burrow efficiently through soil, creating tunnels and moving across surfaces. The bristles also provide stability, helping the worm anchor itself firmly if pulled by a predator or during mating.
Bristles Versus Hair
True hair is a protein filament that grows from specialized structures called follicles, embedded in the dermis layer of the skin. This mammalian characteristic is primarily composed of keratin, a fibrous protein. Hair shafts consist of three layers: an outer protective cuticle, a central cortex containing pigment, and an innermost medulla. Hair growth originates from living cells within the follicle, which continually produce keratinized cells that form the visible hair shaft.
In contrast, worm bristles are made of chitin, not keratin, and develop differently, not from follicles. Worms, being invertebrates, lack this complex follicular system and the keratin-based composition of true hair.