The short answer to “Is a scorpion an insect?” is no. Like insects, scorpions belong to the phylum of arthropods; but they are members not of the insects but of the class Arachnida (arachnids), together with spiders, ticks and mites. In everyday language almost any small creature with legs is called a “bug”, which makes the confusion understandable; in biology, however, the differences between the two groups are clear and easy to observe.
This article explains where scorpions sit in classification, the features that separate them from insects, their closest relatives and why the distinction is more than a matter of naming.
Where do scorpions sit in classification?
The arthropods (Arthropoda), the largest phylum of the animal kingdom, include animals with an external skeleton and jointed legs. Within this phylum, insects (Insecta) and arachnids (Arachnida) are separate classes. Scorpions form the order Scorpiones within the arachnids. More than two thousand scorpion species have been described worldwide; some of the species found in Türkiye are covered in the article on scorpion species living in Türkiye.
| Rank | Scorpion | Insect (e.g. bee) |
|---|---|---|
| Phylum | Arthropods (Arthropoda) | Arthropods (Arthropoda) |
| Subphylum | Chelicerates (Chelicerata) | Hexapods (Hexapoda) |
| Class | Arachnids (Arachnida) | Insects (Insecta) |
| Order | Scorpiones | Hymenopterans (Hymenoptera) |
Features that set scorpions apart from insects
The easiest way to tell the two groups apart is to count the legs and the body sections:
- Number of legs: Insects have three pairs of legs, that is six. Scorpions have four pairs, that is eight walking legs; the clawed appendages at the front (pedipalps) are not counted as legs.
- Body sections: The insect body has three parts: head, thorax and abdomen. In scorpions the head and thorax are fused into the prosoma, followed by the broad mesosoma and the tail-like metasoma.
- Antennae and wings: Insects have a pair of antennae and most of them have wings. Scorpions have neither antennae nor wings; they sense their surroundings through hairs, the comb-like pectines on the underside and sense organs on their legs.
- Mouthparts: Insects have jaws. Scorpions tear up their prey with small pincers in front of the mouth, the chelicerae; chelicerae are a shared feature of the arachnids.
- Breathing: Insects breathe through tracheal tubes spread through the body. Scorpions have four pairs of book lungs on the underside.
These structures are described in detail in the article on scorpion body structure.
How is a scorpion different from a spider?
Although scorpions and spiders belong to the same class, they can be told apart at a glance. A spider's body has two parts joined by a narrow waist; at the tip of the abdomen there are spinnerets that produce silk, and venom is delivered through the pointed chelicerae in front of the mouth. Scorpions produce no silk; their pedipalps have become large pincers, and venom is delivered through the sting on the telson at the tip of the tail. The pectines on the underside are also a sense organ found only in scorpions.
Relatives of scorpions: spiders, ticks and pseudoscorpions
Which group within the arachnids is closest to the scorpions is still a subject of research. Familiar members of the class include spiders, ticks and mites, the long-legged harvestmen (Opiliones), the Solifugae, also called camel spiders or sun spiders, and the pseudoscorpions (Pseudoscorpiones).
Pseudoscorpions are the group whose name causes the most confusion. These tiny animals, a few millimetres long, have clawed pedipalps like scorpions, but they have no tail and no sting. Their venom glands are in their pincers and they pose no danger to people; they may be found between books or under tree bark.
Why does the distinction matter?
The distinction is more than a matter of naming. The body plan, breathing and development of scorpions differ from those of insects: there are no metamorphic stages such as caterpillar or pupa, the young are born alive and growth proceeds through moults. These differences also shape how scorpions live and how long they live; lifespan and development are covered in the article on how long scorpions live.
Scorpions are also an old group in the fossil record: the oldest known scorpion fossils date back more than 400 million years, and the basic body plan of today's scorpions has been largely preserved over this long period. Most of the species whose venom matters for human health are in the Buthidae family. The outer skeleton of scorpions glows strongly under ultraviolet light; this feature, which helps researchers find scorpions at night, is explained in the article on glowing under UV light. General knowledge about insects should therefore not be transferred directly to scorpions; to understand scorpion biology, they have to be considered within their own class.
