An introduction on the biology of tarantulas

Tarantulas don’t have that good of an image. Many people fear them, and in movies, they have often been depicted as monsters. But when you get to know them better, you’ll find out that they are quite gorgeous and fascinating. And next to that, they are surprisingly great animals to have as pets — assuming you are not afraid of these crawlers.

There are 1000 different species of tarantulas identified, and many of them are also kept in captivity. The most common of them kept as pets are the Mexican redknee tarantula, the Brazilian black tarantula, the curly hair tarantula, the Costa Rican zebra tarantula, the pink toe tarantula and the greenbottle blue tarantula, but many more species are kept as pets.

On this page, we’ll illustrate the magnificent and mysterious world of tarantulas. We will talk about their peculiar shapes, their bizarre lifestyle and strange behaviour.

“The arachnids are arguably the most preposterous of the anthropod group that is already an outrageous organism”

Stanley A. Schultz & Marguerite J. Schultz
(The tarantula Keeper’s Guide)

Morphology and anatomy

The morphology — or body plan — is quite different from other bugs. They don’t have that typical insect body plan. The body of tarantulas is divided into two main parts: the thorax (called cephalothorax or prosoma) and the abdomen (called opisthosoma). The abdomen is actually a somewhat wrong word for the rear section. Apart from a segment of the digestive system is located in the “abdomen”, a large part of it is filled with the heart and lungs.

The internal anatomy of tarantulas (Photo by Ryan Wilson, original from John Henry Comstock)

All tarantulas have four pairs of walking legs, which each leg build from seven segments. At the front there is one pair of legged-like appendages, called the pedipalps, and are used for orientation, touching and moving prey. Every real leg has two small claws, where the pedipalps have just one claw.

Tarantulas have two fangs attached to chelicerae (somewhat comparable to mandibles) and are used to manipulate food. With this fangs, it can eject venom to its prey — or predator. It is also used to subduing and somewhat masticating its prey to eat, but mostly the sucking stomachs draw in and suck up the prey meal.

A tarantula is covered with hair, although this ‘hair’ is completely different in shape and anatomical structure from mammalian hair like us, and is often called bristles (other names are spine, setae and trichobothria). However, on its ‘abdomen’ it has urticating bristles. These bristles can be kicked or brushed in the air by the tarantula’s hind legs and penetrate the skin or mucous membranes. When penetrated, they cause much irritation and rash. It will use this defence mechanism when feeling endangered or uncomfortable.

At the outmost rear are two spinnerets where tarantulas make silk for their web. Not all tarantulas make much of a web, however, others make a lot of it.

Life cycle

Tarantulas normally live for years. Many tarantulas are known to reach 20 to 40 years of age, but not much is known exactly how old they become. Tarantulas mature very slowly, and maturing take around 2 to 5 years, but some species take up to 10 years to reach maturity.

Males typically have 1 to 1.5 years to live after they reach maturity. During this time, they quickly go and search for a female to mate. Females, on the other hand, have known to reach up to 40 years. Females usually mate and lay eggs once per year or every other year, unless mating was not successful.


Depending on the species, a female will deposit every breeding season between 50 and 2000 eggs in a silken egg sac. The female guards the egg sac for 6 to eight weeks, where during that time the female stay very close, often always in touch with one leg to the egg sac. The egg sac is often turned once in a while. Turning the eggs prevent the eggs from deforming by the weight of the other eggs when hanging in one position too long.

Baby spiders and spiderling

After hatching, the baby spiders stay in the nest for quite some time. During that time they live from the yolk of the egg sac. After a while, they will disperse to live on their own.

The difference between baby spiders and spiderlings is not that clear. Often from hatching up to the 3rd instar (between every mould is called instar) is called baby spiders, up to the 4th instar until one-third of adult size is called spiderling (and often by enthusiasts shorten with ‘sling’).

Molts and regeneration

Tarantulas only grow when moulting. They shed off their old firm skin (exoskeleton) and come out with a new one that needs to dry and harden. Between moults, they stay the same size.

However, it differs from other bugs that female tarantulas will keep moulting when they are adult, typically after breeding season when the new hatchlings dispersed (but even do so when they don’t have offspring within a season).

When ready to moult, tarantulas will lie on there back, and it looks like if it is dead. The exoskeleton will break open on the thorax, and the tarantula will crawl out of their old skin.

As long as a tarantula has remaining moults, it possesses the ability to regenerate and regrow a lost limb during successive moults. The first moult, after the limb is lost, the limb is still small although fully present. After each moult, the limb will slowly grow to its full size. It will takes up to 2 to 4 years to fully regrow a lost limb.

The Mexican redknee tarantula is one of the most known and common tarantula kept as pets.

Natural habitat distribution

You will find tarantulas in a wide range of different habitats. Tarantulas can be found on every continent, except Antarctica. In deserts, prairies and scrub forests living terrestrial tarantulas. Within rain forests, you can discover terrestrial and arboreal tarantulas. Some tarantulas prefer to live along the water. A few species are known even to be able to dive.

Terrestrial tarantulas prefer more dry habitat. Almost no tarantula can be found in swamps or marshes. There are a few exceptions of terrestrial tarantulas that live in moist forests. All terrestrial tarantulas prefer the compact, stiff solid ground to be able to dig burrows. They are only a rare few species live on sand dunes and areas with very loose sand.

All species of tarantulas can produce silk from their spinnerets. Where arboreal species make a silken ‘tube tent’ to live in, terrestrial species line their burrow walls to make it very stable and make it easier to climb up and down.

Behaviour and temperament

Tarantulas are quite calm, do not move much, and when they do, they often move quite slowly. Some species are also docile and can be handled easily, but it is more that they tolerate it than like it. Some tarantulas can be quite curious. When a new item is introduced to its environment, or when the cover lid is opened from their enclosure, they quickly investigate (or try to escape, perhaps?).

When a tarantula feels threatened, they may stridulate (loud) hissing or buzzing, usually companied by throwing the front legs and pedipalps in the air and leaning on their back legs.

Another exciting behaviour you can observe frequently is that a tarantula is grooming itself, which can be compared with the behaviour a house cat does. It carefully straightening the bristles; however, it has to do it for all its appendages (so each of its eight legs). It’s quite fascinating to see.

When a tarantula is provided food, they move rather quickly to grab their food.

This video illustrates the grooming behaviour of tarantulas.

Food habits

All tarantulas are carnivorous, meaning they eat prey. They feed on almost anything that moves and is small enough to overpower. Their food consists mainly of insects and other anthropods, such as other spiders, millipedes and centipedes. The biggest of tarantulas sometimes even eat small vertebrates when the opportunity arises, like mice, birds, bats and lizards.

They are armed with long fangs and with powerful chelicerae (the mandible like appendages) they can grab a prey pretty quick. Once prey is caught, they don’t have any chance to escape. When bitten with their fangs, the venom helps paralyze and kill the prey.

Tarantulas are not active hunters, and use more a strategy of wait and catch. They are more active on feeding during evenings and nights. However, because of their slow metabolism, they don’t need much food. An average-sized adult tarantula will do perfectly on six to eight crickets a month.

Further reading

Currently, we are developing a general care guide on how to keep and care for your pet tarantula. Come back soon to find more information!

Similar bugs to tarantulas

Fantastic, bizarre, weird, amazing, unique, fabulous, outlandish. Some of the terms that are used to describe tarantulas. There are not many animals alike. However, if you like tarantulas, you’ll probably be also interested in the bugs below:

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