Some insect pet lovers and even new entomologists have a common inquiry – why is a spider not an insect? If you also have the same inquiries on a spider, then this is the best place to get an accurate answer.
Quick answer: a spider is not an insect because they possess 8 legs and 2 body parts. Again, they have no antennae and wings as you find in insects like ants, honeybees, and butterflies.
In this article, I will try (6) to explain the reason why a spider is not an insect with their external anatomy. Again, I will enlist 6 – 8 differences between insects and spiders that might clear everything.
Finally, you will also find the comparison between the specific pet insects (like ants and centipedes) and spiders at the end of the article. So, if you want to understand why not spider considered an insect, let’s continue this article till the end.
Why is a spider not an insect
With the help of the external anatomy of a spider and an insect, you may easily compare their special feature. So, first, let’s discuss the external anatomical facts of a general insect and a spider.
Here, I would like to enlist some of the important external features of a general insect so that you may easily understand – why is a spider not an insect. Let’s see the following external appearance of an insect (in general) –
- An insect has an exoskeleton (external skeleton which supports and protect the insect body),
- You will see 6 legs (3 pairs) in an insect-like ants, butterflies, and honeybees (have some exceptions),
- The body of an insect usually divides into 3 different parts – head, thorax, and abdomen,
- They typically have one pair (2) antennae on their head,
- You will find one or two pairs (2 -4) wings in the body of an insect (in the case of older insects, normally not found in the young),
- Insects lay eggs and may go through metamorphosis (here, the young insect of any species does not look like the mature insect),
These are the major external anatomical features of a common insect. You may find other interesting facts about an insect that might also help you differentiate spiders from them (which will be discussed later in this article).
You know insects are cold-blooded. The baby insect is known as the larva. Some of the larvae may turn into a pupa before becoming mature insects.
If you compare the external features of the insect with a spider, you will find (6) a lot of variation in their legs, body parts, antennae, and also in wings.
So, let’s see the external anatomical facts of a spider.
External appearance (anatomy) of a spider
Spider belongs to the vast group of very successful animals known as an arthropod. Here, I will show you the external anatomical facts of a spider in a very short. Let’s find the below-mentioned external features in a spider –
- You will see a thick hide or shell in the spider (which is known as the exoskeleton),
- The spiders have 2 body parts – cephalothorax and abdomen (abdomen is also known as opisthosoma),
- There are 8 legs where each of these possesses 7 segments and 2 or 3 tiny claws at the tip,
- You will see the pedicel which connects the cephalothorax and abdomen of the spider,
- The pedipalps are 2 sensory feelers attached to the anterior part of the spider’s mouth (short leg-like structure),
- In most of the spider species, you will find tiny eyes (8 – 12) which can detect only light and dark,
- Below the eye, you will find the chelicera in a spider which is actually the mouth part,
- There is an important structure (known as fangs) in the spider’s mouthpart, which use to inject poison,
- Again, spiders have another important structure known as spinnerets, where the silk is released,
So, there is a great variation in a spider’s external appearance or structure compared to an insect’s. The eye, chelicera, fangs, and legs are attached to the cephalothorax part of a spider.
You will also find an interesting fact about the spider’s leg. They will grow back again if any part or full leg is lost.
Normally, you will find 8 tiny eyes on the top of the spider’s cephalothorax. But, the number may vary in different species of spider (8 – 12).
Again, the spinnerets are located at the tip of the spider’s abdomen.
Reason and explain why a spider is not an insect
So, I think you have already learned why a spider is not an insect. From the above information, you may enlist the following reasons for not being an insect –
- The difference in body parts,
- The numbers in legs do not match,
- Absence of antennae in the mouthpart,
- No wing in a spider, and
- Special features in spiders like 8 eyes, chelicera, fangs, and spinnerets, which are absent in an insect,
Now, I will discuss a little about the external parts of an insect so that you may compare them with a spider. I will explain the anatomical facts of below-mentioned structures and parts from an insect –
- Head of an insect – includes compound eye, antennae, and different parts of mouth,
- Thorax of an insect – includes prothorax, mesothorax, metathorax, legs (6), wings (2 – 4), and
- The abdomen of an insect – includes dorsal terga and ventral sterna,
The internal morphology of an insect is somewhat little different than that spider. I will also provide an overview of an insect’s internal morphology with a labeled diagram.
You may read different organ systems of an insect from another different article on insect pets. Again, if you want to know the details of anatomical facts of the external body parts of an insect, you may read the below-mentioned article from insectpet.com –
- How many body parts do insects have?
Okay, let’s get into the short description of the different external features of an insect and compare them with a spider.
Head of an insect
In the structure of an insect head, you will find a series of rigid sclerites or sclerotized segments. The capsule of the insect head comprises a simple eye (ocelli), compound eye, antennae, and mouth parts.
You may hear some terms related to the insect’s head – frons, vertex, gena, and clypeus. Here, the front is the cranial part of the insect head.
Again, a vertex is a cranial area below the dorsum of the insect’s head and behind the eyes. The gena and clypeus are identified in the insect head labeled diagram.
In most insects, you will find one pair of large compound eyes. Exceptionally, you may find the simple eyes (ocelli) in an insect’s head. The number of ocelli may vary from 2 – 4, which detects lower light and small changes in the light intensity.
But, if you notice the structure of the spider head, you will find 8 – 12 tiny eyes which can only detect light and dark. Again, the head of a spider has a wildly variable structure compared to the insect.
You will see the pedipalps in a spider, whereas no such structure is found in an insect. Antennae of an insect
In all most insects, you will find the antennae on their head segment. But, the types of antennae may vary in different species of insects.
4 different types of antennae – setaceous, clavate, filiform, and aristate are commonly found in different insects. There are also geniculate, lamellate, miniliform, pectinate, and serrate types of antennae present in the insect’s head. But, you will not find any type of antennae-like structure in the spider’s head segment.
In the structure of the insect’s antennae, you will normally see 3 different major segments – scape, pedicel, and flagellum. But why are these antennae needed for insects?
These antennae of an insect possess exclusively sensory perceptions, motion, orientation, odor, and others.
Mouthpart of an insect
If you compare the mouthpart of an insect with a spider, you will find a great variation externally. Normally, you will see mandibulate and haustellate mouthparts in the insect.
In general, the mouth of an insect comprises –
- A clypeus (liplike sclerite),
- The upper labrum,
- Jaws like structure or mandibular,
- A maxilla of insects, and
- Labium or lower lip of an insect,
Here, the mandibles of an insect are the highly sclerotized paired structure that can move in the right angle to the body. Again, maxillae are the paired structures in the insect mouth which may also move in the right angle of the body.
The maxillae of the insect possess segmental palps. Here, the labium is the fused structure that also possesses segmental palps. There are no such structures found in the mouthpart of a spider.
Most of the insects possess a mandibulate type of mouthpart, which is designed for biting and grinding solid feed particles. On the other hand, the haustellate mouth part of some insects is designed for taking liquid.
Insects that have a haustellate type of mouthpart also possess stylets. You know, stylet in the insect’s mouth is a need-like projection that is used to penetrate the plant and animal tissue.
Thorax of an insect and spider
You will see a great variation in the structure of the thorax of an insect and spider. That might also make a clear answer to your question – why is a spider not an insect? Let’s see the anatomical facts of an insect’s thorax and compare it with a spider.
The insect thorax shows 3 parts – prothorax, mesothorax, and metathorax which contain hardened plates or sclerites. Here, the sclerites of an insect’s thorax are –
- Dorsal sclerite – known as nota,
- Ventral sclerite – known as sterna, and
- Lateral sclerite – known as pleura,
Each of 3 parts of an insect’s thorax contains pairs of legs. But, you will find wings (paired) only in the last 2 segments of the thorax (upper).
You know there are 6 legs (3 pairs) in the thorax of an insect, where –
- The prothorax of insect – contains fore leg,
- Mesothorax of insect – possess mid-leg, and
- Metathorax of insect – contains hind leg,
In each leg of the insect, you will find 6 major parts – coxa, trochanter, femur, tibia, tarsus, and pretarsus. Here, the tarsus and pretarsus of insects are known as the tarsomeres.
Again, you will see the tarsal claws and arolium at the distal end of the insect’s legs. But, different insects possess a different types of modified legs like – cursorial, raptorial, fossorial, saltatorial, and natatorial.
In most of spider species, there are 8 legs, each of which contains 7 segments and tiny claws. They have a growing back capability if they damage or break.
Again, in the spider, you will not correctly differentiate the head and thorax (fused to form cephalothorax). You will find the peicel (spider waist), which connects the cephalothorax with the abdomen.
Spider has no wing, where insect have
You will find different types of wings in different insect species. These wings of an insect also make them special from the spider.
You may know the different types of insects wings with their anatomical facts from another article of insect pets –
- Insect wing anatomy with a labeled diagram,
Dragonflies, lacewings, honeybees, and termites possess a membranous wing type. These membranous wings are very thin and transparent and have a dark area.
Again, there are halters, elytra, tegmina, and other types of wings found in different insect species. Here, the halters are the extreme modification of the wings, commonly found in different types of files.
Again, the elytra are the hard and heavily sclerotized forewing that may find in the beetle.
Does the spider’s abdomen possess similar features to insects?
The external features of the spider’s abdomen are somewhat different than these of the insect. But, you will find almost similar organs, structures, and parts internally in spiders and insects.
Let’s see how the external appearance of an insect varies from the spider.
In the external anatomy of the insect abdomen, you will find different segments dorsally and ventrally. Here, the dorsal segments of the insect abdomen are the terga, whereas the ventral segments are the sterna.
Generally, the number of dorsal and ventral segments may vary in different insect species. But, you may find 8 – 10 segments (dorsal and ventral) in the abdominal region of an insect.
You will also see another structure (known as spiracles) in the abdomen of an insect. These spiracles of insects locate between the terga and sterna.
At the caudal part of the insect abdomen, you will find the cercus (dorsally). Male reproductive structure finds at the level of the 8th segment of the insect abdomen.
Again, the female reproductive structure locates at the level of 8 – 9 segments of the insect abdomen.
Social behaviors of an insect
Important social insect like ants, wasp, honeybee, and termite exhibits certain complex behaviors and live in society. These social behaviors also make you understand – why is a spider not an insect.
Let’s see some of the important social behaviors of an insect.
- Most of the insects live in a society where you will find several generations in a single nest at a time,
- They involve together in building their nest and protecting against enemies,
- Parental care is the distinct behavior in the insect species,
- The worker members of the insect colony care for eggs, and larvae, collect food, and repair their nest,
- They also have cooperative care and a greater rate of reproduction,
- You may see the polymorphism in the insect species (in a different form),
- They have great communication with other colonies,
- Most of the insect species share their feed with others,
- You will see the swarming behaviors in the insect species where a large number of them come out from their nest to avoid overcrowding,
This is an important behavior found in most insects, normally in summer or winter. Insects perform this swarming behavior mostly for feeding and migration.
By this unique behavior, an insect may form a new colony.
But, you will not find such kind of social behavior in the spider. So, they (spiders) are also different in the case of behaviors from the insect.
List six differences between insects and spiders
Now, it will be easy for you to distinguish between insects and spiders. Here, I will list some of the major differences between insects and spiders in table 1 –
| Features | Insects | Spiders |
| Body segments | 3 (head, thorax, abdomen) | 2 (cephalothorax, abdomen) |
| Legs | 6 (six) | 8 (eight) |
| Antennae | Present (2) | No antennae |
| Wings | 2 pairs (4) | No wing |
| Eyes | Compound and simple | 8 – 12 tiny eyes |
| Pedicel | No pedicel | Connect cephalothorax and abdomen |
| Pedipalps | No pedipalps, But possess antennae | Sensory feelers in front of spider |
| Spinnerets | No spinnerets, have cercus | Locate tip of abdomen |
Table 1 shows the basic difference between an insect and spider find in their legs, body segments, antennae, wings, eyes, and pedicels.
Which is not an insect like a spider?
There are some species like bugs, centipedes, millipedes, worms, crabs, and lobsters that are sometimes considered an insect. But, they are not real insects as they do not fulfill the external anatomical features of true insects.
Millipedes are not the true insect because of –
- They (millipedes) possess more than 3 segments in their body,
- Each body segments of the millipede possess 2 pairs of legs,
- But, they have one pair of antennae like the insect,
Again, bugs are also not the true insect as they have 14 legs and many segments in their body. The worms are not true insects as they have no exoskeleton. In addition, worms possess several segments in their body.
The crabs and shrimp are not also the insect as the several segments of the body fuse together. Again, they have more than 6 legs (the number of legs may vary in different types of crabs and shrimps).
Is a centipede an insect?
No, a centipede is not an insect. If you see the external appearance of a centipede, you will see the followings –
- Centipede has several body segments (not match with insect),
- You will see 1 pair of legs in each segment of the centipede’s body,
- Last 1 pair of legs modified to form fangs in centipedes,
But, you will find 2 antennae in the cranial segment of a centipede. The centipede is not under the insect as the body segments and legs are more than a normal insect.
Suggested article from insect pet for you –
- What insect has the longest tongue?
- What are the excretory organs of insects (ant) called?
You may learn the details features of insects from other different articles of insect pets. If you are interested in keeping an insect as a pet, you may check the insect pet care guide here.
Frequently asked questions on insect and spider
In this article section, I will try to provide short answers to frequently asked questions about insects and spiders. Most people (insect lovers and new entomologists) have some general inquiries on – which are bugs, insects, and others.
Now, let’s see the commonly asked questions about insects and spiders.
Are spiders animals or insects?
Spiders are neither insects nor animals; they are considered arachnids under the class Arachnida. Under this Arachnida class, you will also find scorpions, ticks, and mites.
All these arachnids have 2 segments in the body – cephalothorax and abdomen. They have 8 legs and 1 pair of chelicerae but have no antennae.
Why ant is an insect, and a spider is not?
Ant is a true insect and is considered the best-friendly and most beneficial pet. The external appearances of an ant have similar features of an ideal insect.
The true insects like ants are beetles, wasps, moths, flies, termites, and others (listed here). In an ant, you will find the following external features in common with other true insects –
- Ants possess 3 distinct body segments – head, thorax, and abdomen,
- You will see 3 pairs (6) of legs in the ant’s body,
- Ant has one pair of antennae on the anterior part of its head,
- You will find diverse modifications of appendages in an ant,
As most of the external features are similar (see the list and compare), so ant is a true insect. Again, the social behaviors of an ant are similar to the ideal insect.
Ants are considered one of the most social insects on this planet. They love to work together and communicate with each other for feeding and migration.
Conclusion
I hope you got your actual answer on – why is a spider not an insect. As the spider has 2 segments in the body and 8 legs, they are not considered as a true insect.
In addition, a true insect possesses 3 defined segments – head, thorax, and abdomen in their body and 6 legs. Again, true insects have antennae and wings (like – ants).
There are 2 antennae present in the anterior part of the insect’s head. The numbers of wings are 2 pairs in a true insect. But, a spider has no such antennae or wings; thus, they are not insects.
