Spineless? Invertebrates

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.

Cockroaches Use Leg Spines for Traction
The American cockroach, Periplaneta americana

About jjneal

Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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11 Responses to Spineless? Invertebrates

  1. Douglas Triplett says:

    It is ironic that insects are called spineless, when insects like cockroaches have tons of spines on their bodies. It is fascinating how they are able to use spines like athletes use cleats. They have amazing traction from those tiny little spines. I noticed while watching my cockroach that the spines give it the ability to crawl almost anywhere, my cockroach even climbed up glass!

  2. As Douglas pointed out before, these spines aid in traction… even traction up glass as I have witnessed. This is just one more of many examples about how insect features or appearance, however “hideous” to the human eye, are incredible in the way that they help in adapting to environmental factors. Along the same lines, many of these “hideous” features are simply foreign to humans, such as spines, antennae, or multiple legs or eyes. So an understanding of function and purpose truly need to be understood when considering an insect and its usefulness and beauty. Beauty may not come in the same form that humans are used to; beauty may simply be an incredible function or ability.

  3. Ryan Chaney says:

    I never really viewed insects as spineless before reading this article. I didn’t really connect the thought that an exoskeleton does not pass for having a “spine.” Also I never thought about how a cockroach could maneuver itself through cracks with its physical make up. I find it interesting how the spines create so much traction for them.

  4. Steve Schnell says:

    I decided to read this article because it was about cockroaches and i currently have one as a pet. I enjoyed the irony of the post but i also enjoyed learning more about my pet. The other day in my entomology class our professor touched on the fact that insects do not weigh enough to create traction so they have other means of gaining it. After reading this I decided to test the roach’s ability to walk on different surfaces and the article didn’t lie because it could even get traction to walk on a buttered plastic surface.

  5. Mitch Steichen says:

    It’s amazing to imagine a spine that aids in traction for an insect. Without the spine, which is found in the cockroach, it would be nearly impossible for the insect to grip anything at all. It’s interesting to see that such a feature on an insect helps it mobilize wherever it goes. Though, these insects may not be physically appealing to humans, it is the functionality of these spines on insects which help making each insect unique. This individuality between insects proves sciences many features that are amazing to look at on a daily basis.

  6. Clinton Kominowski says:

    Upon reading this post and its comment I also thought of my cockroach and it’s ability to climb various surfaces but I haven’t had the opportunity to test this myself. It’s very interesting to think of the idea that insects have such a large disadvantage to moving around because of their size. Insects must have an extremely hard time moving around on windy days, maybe that is something to test with a cockroach but the main thing I’m curious about is the size that insect were before. When insects were much larger did they necessarily need these extra appendages to move as they do now?

  7. Young Jae Kim says:

    Insects being spineless? When I read the title, It suddenly grabbed my attention. In my understanding, every live objects, including insects and mammals, have bone structures. It’s a surprising fact that having a exoskeleton does not really count as having a spine. Plus, I now understand why it’s so hard to pick up a cockroach because of almost minimal traction I get when grabbing with my hand. It’s just facisnating that cockroaches can move on any, even a greased surfaces.

  8. Derrick Spight says:

    I think it’s wierd that insects are called spineless but have spines. I like the way it is explained why insects have spines and the way that they are formed. And I like how he described the cockroach and its non wimpy spine.

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