Are spiders insects?

Spiders are commonly confused with insects. Here you learn how to distinguish these animals.

Arachnology is a science not only concerned with spiders, but with other arachnids such as scorpions or harvestmen. Although spiders are the primary subject on my weblog, I’d like to give a quick introduction to other animals that sometimes get confused with our eight-legged friends.

Arachnids form an entire class within the realm of systematic biology. Here, I’d like to show you how you can easily distinguish spiders from insects and other arachnids and what the key characteristics of these animals are.

Spider or Insect?

Some people think that spiders are a type of insect. That is not the case. Although spiders and insects are both arthropods, they belong to two separate groups of animals. These groups are referred to as classes within biology. While Arachnids belong to the subphylum chelicerata, insects belong to the subphylum hexapoda. Translating “Hexapoda” roughly results in “six-legged”. These classes are thus easily distinguishable by the number of their legs. Animals belonging to the class Arachnida have eight legs, while Insecta only have six. An additional feature to distinguish insects from spiders are the number of visible body parts. Spiders are divided into two parts, whereas insects have three distinguishable segments.

Learn more:
A quick Introduction to Spider Anatomy

Spiders and other Arachnids

Let’s increase the difficulty a little. As mentioned above, arachnids form a pretty diverse class of animals. Within this class are multiple orders of animals, including the order of spiders Araneae. Harvestmen, as an example, make up to their own order Opiliones within the class of arachnids.

Harvestmen look like spiders but aren’t. That’s because, unlike spiders, Opiliones have neither venom glands nor the ability to produce silk. And, if you look closely, the body of an Opiliones appears only as a single segment.

Learn more:
The Infraorders of Spiders

This can also be seen in mites. Although most of them are extremely small, and therefore difficult to spot with your naked eye, their bodies appear not as nicely segmented. Additionally, some of their legs are appear to be attached to their opisthosoma, which is never the case in spiders.

Sources

• Header Image: Foto von Ngan Nguyen auf Unsplash
• Image “Weberknecht beim Trinken”: Macrophoto from Valentin Gutekunst on makro-treff.de
• Image «Rote Spinne»: Macrophoto from UVO on makro-treff.de