Are Tarantulas Reptiles, Mammals, Insects, or Arachnids?

Tarantulas are not reptiles, nor are they mammals. If you said they’re insects, that’s not quite right either, but you’re getting closer. The correct answer is that tarantulas are arachnids!

Arachnids are a class of join-legged invertebrates. This means that they do not have spines.

Another common feature among arachnids is that they have eight legs. Types of invertebrates include scorpions, ticks, mites, and spiders. Tarantulas are spiders and thus fall under the arachnid category.

If you’re interested in learning more about what tarantulas are (and what they are not), keep reading and we’ll go a little deeper. I promise that it will be very interesting to discover why tarantulas are not considered insects, reptiles, or mammals.

Why are tarantulas not mammals?

Tarantulas are not mammals because they don’t fulfill the criteria that they need to meet in order to be classified as a mammal.

The five characteristics that an animal needs to have in order to be a mammal are these:

  1. They are covered with hair or fur
  2. They are warm-blooded
  3. They are not born in eggs but are born alive
  4. They drink milk from their mother
  5. They have large brains

So, let’s see which boxes tarantulas check, shall we?

  1. ❌Tarantulas do have “hairs” on their legs and abdomen, but these setae differ from mammal hairs
  2. ❌Tarantulas are cold-blooded!
  3. ❌Tarantulas lay eggs, their babies are not born alive
  4. ❌They do not produce milk and do not feed their infants at all
  5. ❌They have relatively small brains and are not all that intelligent

As we can see, tarantulas are not even close to being considered mammals as they don’t meet a single criterion in order to be considered one.

Examples of mammals, tarantulas do not fit in with them!

Why are tarantulas not reptiles?

If you thought that tarantulas might be reptiles you’re a little closer to the mark. However, they don’t meet the criteria for being a reptile either.

According to the University of Georgia, there are 5 traits that all reptiles have. These are:

  1. They are vertebrates, which means that they have a backbone.
  2. Their bodies are covered with scales
  3. Reptiles are cold-blooded
  4. Reptiles produce eggs or bear live young
  5. They fertilize their eggs internally
  6. They have at least one lung

Let’s see which of these boxes tarantulas check.

  1. ❌They do not have a backbone
  2. ❌Their bodies are not covered with scales
  3. ✔️Tarantulas are cold-blooded
  4. ✔️Tarantulas produce eggs
  5. ✔️They do fertilize their eggs internally
  6. ✔️Since they can breathe above water, tarantulas do indeed have lungs

So, tarantulas check 4 out of the 6 boxes. However, in order to be classified as a reptile, they have to check all the boxes. So, tarantulas are not reptiles.

Examples of reptiles. Our eight-legged friends do not fit here either!

Why are tarantulas not insects?

Now we get to the good stuff. If you ask 100 people whether tarantulas are insects I’m sure a decent portion of people will say yes. This is because many people believe spiders to be insects, but that’s not actually the case!

Let’s do a similar comparison as before to see why these big spiders are not considered to be insects.

According to Wikipedia, insects have 5 defining traits. These are:

  1. Insects have an exoskeleton
  2. They have a three-part body consisting of a head, thorax, and abdomen
  3. They have three pairs of jointed legs
  4. Insects have compound eyes
  5. They have one pair of antennae

Let’s once again check the boxes to see which traits tarantulas do and do not have.

  1. ✔️Tarantulas do indeed have an exoskeleton. They shed this several times in their life by molting
  2. ❌The bodies of these large spiders consists of two parts, the cephalothorax, and the abdomen
  3. ❌They have eight legs instead
  4. ❌Tarantulas have what’s called “simple eyes”
  5. ❌They do not have antennae

As you can see, while tarantulas are often mistakenly called insects, they’re actually quite far from it.

The only thing they have in common with them is that they both have an exoskeleton. In fact, tarantulas technically have more in common with reptiles than insects!

Examples of insects

Why are tarantulas arachnids?

So, now we’ve established that tarantulas are definitely not mammals, reptiles, or insects. Let’s see how they stack up with the traits that arachnids have.

These are the characteristics that all arachnids have:

  1. Four pairs of legs (eight total)
  2. Arachnids also have two additional pairs of appendages. The first pair, the chelicerae, serve in feeding and defense. The next pair, the pedipalps, help them feed, move, and reproduce.
  3. They do not have antennae or wings.
  4. Their body is organized into the cephalothorax, a combination of the head and thorax, and the abdomen.
  5. They have at least one lung

Once again, let’s see how our favorite eight-legged friends compare to this list of criteria.

  1. ✔️ Tarantulas do indeed have eight legs
  2. ✔️ They have fangs, which are their chelicerae and pedipalps
  3. ✔️ They do not have antennae or wings
  4. ✔️ They have a cephalothorax
  5. ✔️ They have lungs

As you can see, we’ve got a perfect match! Tarantulas match all the criteria to be considered an arachnid. As you might know, there are many different tarantula species. However, they all fit the criteria above, so they’re all part of the arachnid class.

Collage of arachnids. The tarantula is in the top left.

Are tarantulas spiders?

Yes, tarantulas are spiders.

Wait… didn’t we just say that they were arachnids?!

We did, but both are true. Spiders are scientifically called Araneae, which is an order, while arachnids are a class. What this means is that tarantulas are in the order Araneae, which is part of the arachnid class.

If you want to go even deeper, the arachnid class is part of the Chelicerata subphylum, which is part of the Arthropoda phylum, which is part of the Animalia kingdom. So, tarantulas are animals, arthropods, arachnids, and spiders all at the same time.

Other animals that are part of the arachnid class are scorpions, mites, and ticks, as they all fulfill the criteria for arachnids listed above.

Final words

So, there you have it. Tarantulas are arachnids, not reptiles, insects, or mammals. They are arachnids because they fulfill the 5 criteria that all arachnids have, while they do not fulfill the criteria that insects, reptiles, or mammals share.

In the end, all of these distinctions and characterizations are man-made, but they’re still a useful way to put animals into categories, which is something we humans love to do because it makes the world a lot less cluttered and gives us a better understanding of the world around us.

Jesse A.