Do Spiders Have Bones?

Spiders are well-known for spinning webs to trap insects. Their movement is fascinating! How exactly do spiders move? Do spiders have bones? How do spiders maintain their body structure?

Let us understand the answers to these questions in detail!

Do Spiders Have Bones?

Like many other animals and all insects, spiders do not have bones. Instead of bones, spiders have an outer skeleton known as the exoskeleton. What is an exoskeleton ? An exoskeleton is a hard covering used for support and protection. The exoskeleton is made of two layers: a thin outer layer called the epicuticle and a thick inner layer called the procuticle . These overlapping layers of the exoskeleton are made of proteins. Specifically, the procuticle is made of a protein called chitin .

While the exoskeleton protects the spider, it soon becomes too restrictive as the spider grows. Thus, spiders shed their old exoskeleton and form a new one. This process is called molting . How does the exoskeleton help spiders instead of having bones? First, let us understand the body structure of spiders.

The body of spider is divided into two parts: the cephalothorax and the abdomen . The cephalothorax contains the stomach and the brain of spiders. The head and a region called the thorax fuse to make the cephalothorax. The legs of spiders attach to the surface of the cephalothorax. The top of the cephalothorax is protected by a structure known as the carapace . The bottom of the cephalothorax is covered by a structure called the sternum .

In place of bones, the exoskeleton acts as a system of support and protection in spiders. The muscles are joined to the exoskeleton instead of bones, allowing for proper movement. How do spiders or other animals with exoskeletons move? Let us understand this in detail.

What Animals Have Exoskeletons?

Apart from spiders, many animals have exoskeletons instead of bones. Most animals having exoskeletons belong to a group of animals known as the invertebrates . The invertebrates are a group of animals lacking backbones. Insects are the largest group of organisms (within the invertebrates) that have an exoskeleton. Other than insects, crabs, lobsters, shrimp, spiders, ticks, mites, scorpions, and many other animals have exoskeletons. Like spiders, the exoskeletons of these animals are also made of chitin.

How do animals with exoskeletons move? Even though their exoskeletons are hard, bendable parts or joints in the exoskeletons allow the animals to move freely. Sometimes, small holes known as spiracles are also present in the exoskeletons. Spiracles allow such animals to breathe on land.

Like spiders, most animals with an exoskeleton show the process of molting. Since the exoskeleton does not grow with the growing internal parts, such animals must shed their older exoskeletons and form newer, larger exoskeletons. In the timespan between the two exoskeletons being fully formed, the animal is left completely unprotected. What about animals having a slightly different exoskeleton? Such animals include clams, oysters, mussels, and snails! These animals have an exoskeleton that is known as a shell . Shells are made of a material called calcium carbonate (and not chitin). Animals with shells do not show the process of molting. Rather, the shell grows along with the animal!

Glossary

Exoskeleton: outer or external skeleton

Epicuticle: thin outer layer of the exoskeleton

Procuticle: thick inner layer of the exoskeleton

Chitin: a protein substance found in the exoskeleton of arthropods

Molting: the process of shedding an older exoskeleton and growing a new exoskeleton

Cephalothorax: the fused head and thorax of spiders

Abdomen: the last segment of the body of spiders

Carapace: a covering to protect the top of the cephalothorax

Sternum: a covering to protect the bottom of the cephalothorax

Invertebrates: animals without a backbone

Joint: a bendable region in a skeleton

Spiracle: a small opening or hole meant for breathing

Shell: a type of exoskeleton made of calcium carbonate

Calcium carbonate: a chemical compound with the chemical formula CaCO₃

Flesch Kincaid Grade Level: 8.9

Flesch Kincaid Reading Ease: 50.5

References

“Exoskeleton.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://kids.britannica.com/kids/article/exoskeleton/399448.

“Funnel-Web Spider Shows Vulnerable Side While Moulting.” Institute for Molecular Bioscience – University of Queensland, 19 May 2020, https://imb.uq.edu.au/blog/2020/04/funnel-web-spider-shows-vulnerable-side-moulting.

“What Is Spider Silk?: Spider Silk Types & Facts.” Orkin, Orkin, 3 Aug. 2021, https://www.orkin.com/pests/spiders/spider-silk-facts-and-information.

“Spider.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/animal/spider-arachnid.

“Spiders, Facts and Information.” Animals, https://www.nationalgeographic.com/animals/invertebrates/facts/spiders.

“Spiders.” The Australian Museum, https://australian.museum/learn/animals/spiders/