Insects are often described as “spineless” because they lack a backbone and internal skeleton. It is true that insects lack a backbone but they do have spines.
In insects, spines are cellular outgrowths of the insect exoskeleton that are coated with cuticle. To form a spine, the single layer of epidermal cells that secretes the insect cuticle forms an outgrowth in the shape of a cone. These cells secrete cuticle that hardens over the underlying cells in the shape of a thorn-like spine.
Cockroach spines are not at all wimpy. They are rigid and prickly, heavily sclerotized cuticle. The cockroach spine is a projection that can grip the surface the same way an athlete’s cleat will grip into turf. The spines protrude at different angles which ensures that some of the spines are in position to grip uneven surfaces.
Anyone who has been spelunking understands the difficulty in crawling through slick, narrow passages with inadequate traction. Cockroaches have numerous adaptations to life in cracks and crevices. Leg spines are one such adaptation. Appendages that can push against a surface without slipping are beneficial. Cockroach spines are small enough to fit into the natural valleys and pits in the fine structure of the rotting wood that lines the cervices that cockroaches inhabit. Multiple spines provide multiple sites that can grip the surface. The extra grip provides sure traction for efficient movement in tight quarters.
When the cockroach leaves its crevice, the spines give the cockroach the same sure grip that track stars get from their cleats. Spines provide multiple points of contact between the insect and its surface. As the cockroach runs across uneven ground, some of the spines may be suspended above the surface while others will grip. The sure traction allows the insect to get a good push against the ground with each step it takes.
Far from being “spineless” invertebrates, cockroaches quite rigid and rather “prickly’ to hold. Anyone who has tried holding a cockroach can readily feel the spines of their legs grip the surface of the skin.