Are Spiders Insects?

With eight legs, multiple eyes, and fangs that can inject venom, spiders are a terrifying sight for some. Despite their menacing appearance, these little critters are important components to every ecosystem they’re found in. Many people refer to spiders and other creepy-crawly things as insects. They do have lots in common with insects, and they even look and behave a lot like our six-legged friends. But, are spiders insects?

Technically speaking, spiders are not insects! Why aren’t they exactly? We’ll look into a few main reasons why spiders and insects are so different. But first, let’s break down what spiders and insects have in common, which is actually quite a bit.

To understand the similarities and differences between spiders and insects, we have to cover a bit of taxonomy. Taxonomy is the science of classifying all living things. Spiders, insects, fish, birds, and humans all fall into the Kingdom Animalia. Pretty much every animal is able to breathe and move, unlike plants and fungi. Additionally, animals are multicellular, unlike bacteria. Let’s dive deeper into the world of taxonomy and discover more about the classification of spiders and insects.

Photo by Jeff Burcher

Spiders and Insects Are Arthropods

Getting more specific, we move into the Phylum of Arthropoda. Spiders and insects are still together in this group, as are crustaceans, centipedes, and the famous extinct Trilobite. Arthropods are an incredibly successful group of animals and can thrive in the deep ocean, wet forests, and extremely hot deserts. But what makes an arthropod an arthropod?

First of all, arthropods are invertebrates. Unlike mammals, birds, and reptiles, they lack a spinal column. Instead, arthropods have super hard exoskeletons on the outside of their body, made up of stuff called chitin. Chitin is actually very similar to the material that makes up our very own hair and fingernails! In order to grow, an arthropod must shed its exoskeleton and create a new one. Here’s an awesome video of a cicada shedding its exoskeleton.

Another defining characteristic of an arthropod is having segmented legs. In fact, that’s exactly where the name arthropod comes from. Arthro means jointed, and pod means leg. There are a few other more technical characteristics of arthropods, but we won’t worry about those.

(1) Four pairs of legs, (2) cephalothorax, and (3) abdomen

Spiders Are Not Insects!

The next taxonomic level down is where spiders and insects lose their similarities. Spiders are in a class of animals known as arachnids. Spiders, scorpions, mites, and ticks are all different kinds of arachnids. Perhaps the biggest difference between arachnids and insects are the number of legs they have. One of the defining characteristics of spiders and other arachnids is that they have 8 legs. Insects, on the other hand, only have 6. This difference may not seem that significant, but it’s one of the most important things that separate these two classes of animals!

Next up is the number of body segments. Spiders have two segments – the abdomen, and the cephalothorax (which is a combination of a head and thorax). Insects boast three distinct segments – an abdomen, a thorax, and a head. Although they serve essentially the same functions, the body segments are another characteristic that spiders and insects do not have in common.

On the topic of body parts, insects have developed wings for flight. Nearly all insect species are capable of flight – even ants, although it’s usually just the queen who’s able to. Spiders and other arachnids are not able to fly. Which is good for us, because if they could, they would be about a thousand times scarier.

Of course, the differences between spiders and insects don’t stop there. They have very different roles in their ecosystems as well. Mainly, spiders are carnivores and hunt for their food, usually by using webs made of silk. Many insects (but not all of them!) are herbivores and are often a tasty snack for other animals, including spiders.

So, now you know! Contrary to what many people believe, spiders are not insects. We’ll leave you with this super cool video of a peacock spider dancing to attract a mate.