Guide of the big hairy spiders from the land of Gardel

by Fernando Pérez Miles, Fernando Costa, Mario Lalinde, Antonio Mignone and Anita Aisenberg.

In these pages you will find out: how tarantulas look like, where and how long they live, how they feed themselves, how they reproduce, if they are dangerous, who are their enemies, what species live in Uruguay and how you can breed them, myths and legends about the tarantulas.

Also, you will have the access to a key for identifying tarantulas. And something else, too…

What are they?

How can we identify them?

Males and females

Courtship and Mating

When the tarantula gives birth

How can we breed them?

The best pet

Be careful with those hairs


Species of Uruguay

How do we recognise the different tarantulas?

Key for identifying each species

The big Grammostola

The medium- sized 

The small ones



For sending us an e-mail: Fernando Costa

These pages are designed and updated by Mario Lalinde  


What are they?


In general they are big, very big and hairy. In these lands they are known as  ‘arañas pollito’ (chicken spiders), but they have different names all around America: ‘arañas mono’ (monkey spiders), ‘ pica caballos’ (horse stinger) and North Americans call them ‘ bird-eater-spider’ or simply ‘bird spider’. But the most extended name is Tarántula or the international Tarantula. Many societies of tarantula fans have names as: The British Tarantula Society and the American Tarantula Society, for example.


Tarantulas belong to the Theraphosidae family. This family is mainly distributed in the New World, showing the greatest number of species in South America. Analysing the distribution, it could be possible that these animals appeared on Earth more than 150 million years ago, when Africa and South America were still joined (Do you remember Gondwana?… Neither do us).  

How can we identify?

Although most of them are big and hairy, this is not enough to identify them. Some species are small and even the big species, of course, are not born with that size. Moreover, there are other species more or less hairy, that are not ‘pollito’. As always, biology has its exception. So we are forced to give you some technical details. 

Let’s go step by step. Look at the figures.

The chelicerae of these spiders (the organs they use for biting) are more or less horizontal and they move in parallel. But what definetely lets us recognise a tarantula are their legs. The last segment of the legs (that is called tarso) has a kind of hairy brush, the scopula, and a tuft of hairs under the nails which is called claw tuft. These organs allow them to stick to smooth surfaces and climb. With these three characteristics you can’ t mistake them! And if you still are not sure, you can check out if they have the eight eyes joined in a small pile, characteristic of the tarantulas.


Males and Females      

As in other spiders species, the females are heavy-built and the males are thin. What is the reason? Tarantula males need to be prepared for walking and walking searching for the females and evading dangers on their way, thanks to their long legs. On the contrary, females are more sedentary; they live in caves,  need to accumulate reserves and maintain numerous eggs of an important size which take up a lot of space in the abdomen: they are strong and fat. Adult males are copulating-machines: they do not live too long, have few reserves and are bad hunters, so they do not have the possibility to recover much of the strength lost. As females live five, ten or more times the life of a male, in the nature you can find more females than males. That is why males are considered ‘ copulating-machines’ till they die. Also because of this, the arachnologists in general equate: presence of males= sexual period. 


As would be expected for animals that have short lives and copulate a lot of times, the matings are short, just a few minutes. The sperm is carried  by males inside some specialized organs, the bulbs of their palps.  During copulation, sperm is transferred from the male palp into  the female genital organs of sperm storing (the spermathecae), that end in the epigastric furrow



Now: how can a male of any spider, that has the testes inside the abdomen, transfer the sperm to the female? This handling is unique in the Animal Kingdom and is called ‘sperm induction’. The male spins a web - that in tarantulas is enormous, a real sheet- and places himself under the web, facing upwards, and deposits in the web a drop of sperm. Then he places himself on top of the drop and moves quickly and alternatively the palps, touching the drop with the sharp ends of the bulbs. In this way, he introduces the sperm into the palps and he is ready for inseminating.



Courtship and copulation  


The males are capable of detecting the presence of a female by perceiving chemical substances (feromones) that she leaves in the web that surrounds the entrance to her cave. Males start the courtship, in general, vibrating their bodies with spasmodic movements of their third pair of legs. Probably, this means seismic communication through the soil, and we do not rule out the possibility of the production of sounds, inaudibles for us, emited by stridulatory organs, which several of them possess. It is also frequent, an alternative palpal drumming against the soil. When the receptive female goes out and faces the male, in general at the entrance of the cave, she opens her chelicerae.

One gets really scared: such a female, big and hungry…. she is going to destroy that poor male. But no, sexual canibalism is strange, very strange. Moreover, this threatening attitude from the female is necessary for the mating to occur. The males seize the female’ s dangerous fangs with a special hook or apophysis that only males have at their front legs (distal extreme of the tibia), and which is specialized for that: holding tight the female’ s chelicerae. In other words, if the female is good to her partner it is impossible to mate (perhaps the male says something like: Sweetheart, you look so nice when you get angry…).





In this position, danger transforms into pleasure. The male lifts up the female and places himself under her, stretches his palps and inserts them alternatively a few times, transferring the sperm into the female genitalia. 




Later, covering his retreat with vibrations, fondlings and other cares, the male unhooks the chelicerae of the female and goes away with some swiftness but without panic. Like that, the task is carried successfully!

This is his life: wandering (in general, through the night) looking for females, courting, copulating and charging again his palps by sperm induction.


When the tarantula gives birth


During the summer the female places her eggs on a thick ‘silk dish’: only at this moment the sperm comes out from the female spermathecae and contacts the ovules and the fecundation occurs. The female covers the eggs with new layers of silk and rounds the eggsac or bag of eggs, in general free, and she jealously takes care of it inside her cave. During this period, the female does not feed herself and she loses a lot of weight.



Most of the times, she closes the entrance to the cave with soil or silk. Tarantulas make only one eggsac per year and they do not lay many eggs: from some tens to a few cents per eggsac (other spiders, smaller than tarantulas, lay thousands each period and ,obviously, later they die). When the spiderlings emerge, their mother is very tolerant with them and they are tolerant with each other. These juveniles will move away after moulting one or more times. 


The life of a tarantula: A long and winding road


The life of a female is long. For example, the big Grammostola  which we have bred at the laboratory, live up to twenty years as adults and they take ten years to get to that condition. So, in captivity, they can live up to thirty years. Thirty years! Two times the life of  a dog, and the same than a horse! This just females; males live much less. All the spiders change their skin (moult) for growing because their skin is the external skeleton and it is rigid. The old skin keeps more or less the shape of the spider and you will feel as if you were watching two spiders. Something curious: most of the spiders stop moulting when they are adults, but female tarantulas keep on moulting and moulting during their whole lives. Could it be the reason to explain why they are so big? 



On the opposite, males do not moult after they become adults.The moults are not just for growing, but also they give the possibility to replace worn-out structures, specially urticating hairs lost during life matters. Did you say urticating hairs? Do not worry. We will talk about this later on.


The tarantulas have a long and peaceful life; they are more active at night and generally they live hidden in caves or under stones. On the contrary, when males are ready to do so, they transform into wanderers and spend their lives looking for the females (What a thing!): nearly they do not eat, and very often they die under wheels, sticks or shoes. It seems that being a male is a risky and adventurous profession, a very different life style compared with the one of the females and juveniles.



How can we breed them? 


One fish-bowl (without water); soil; some stones and a container for the water. And remember to cover it cause they climb (remember that they have claw tufts and scopulae). It is convenient that the fish-bowl should have a good size, without exaggerating, because in the nature they spend most of their lives inside their small caves. If it is a digger- tarantula, it would be nice to add an artificial shelter against the glass, so you can see it. If the spider lives under a stone, it would be convenient to add the shelter in a way that you can see the spider. It is important to remember to give them always fresh water supply; besides, they can resist the dehydration but it is better not to test them. But feeding them is different. Mainly, they eat insects. Of course, with tiny flies it can be a nightmare: like feeding pigs with biscuits. They can be cockroaches, grasshoppers, beetles, crickets, or any small living being that walks, but it must be alive. The activity of the spider and the size of its abdomen are the best indicators to know when to feed them. You can give them food once a week during the summer. In winter, they reduce their activity and nearly they do not eat. They should be raised individually: never put two spiders together; you will get just one: a fat one.


The best pet


Do not try to take it for a walk with a leash… Think about ornamental mascots as fish, hamsters or mice. Those small animals which stay at home in cages and according to the consumer’s likes, can move from the garage through the living, or even to your bedroom (perhaps beside your bed?). Excepting the dear tarantulas, all the other animals will need a lot of attention. You will have to change the water, feed them daily, put them with aerators which are really noisy, or change their ‘beds’ when you cannot stand anymore that disgusting smell. And that is not all, their lives are short, too short. And their deaths bring a huge family problem, with terrible cries from the small ones. Or the white lies: ‘ the vet took him to a place where he will be better’. Once again, the marvellous tarantulas win the championship: they do not make noise, they do not have smell, they can spend weeks without eating, they do not need a big space, they do not pay taxes, they do not transmit illnesses… and their lives are long, till thirty years. That is why when the spider dies, your children will be married and with sons and they will not cry so much. With all these virtues, it will look beautiful to you! And you are not the only one. You should know that in the United States, England, France and Germany, there are important clubs for tarantula fans, and they organize expositions, contests and have specialized magazines with classified adds included.



Be careful with those hairs    

In spite of their size and their scary aspect, the bites of these spiders are not dangerous to the human. Of course, if by chance they bite you, it will hurt a little bit (I am sure that when you prick yourself with a needle or a nail, it will hurt, too). But the toxin that they can inoculate is not dangerous, it just hurts as a wasp sting and it is over in a few hours. We tell you this because we have a personal experience: Pérez was bitten by a great Brachypelma vagans at the jungle of Chiapas (the first bite in twenty years of work… and for being overfamiliar). Other friend, Carlos Toscano, was also bitten by two Acanthoscurria suina and both - Carlos and the spiders - survived without any consequence. But what all the american tarantulas -and nearly all the uruguayans, too- have on the dorsal side of the abdomen is a patch of specialized hairs. The spider throws these hairs to the air by rubbing the hind legs, as a defence when she is disturbed. The hairs can cause irritation when they contact the skin or sensible tissues like the mucous membranes. They are called urticating hairs. If you look at the figures, you will probably understand why they say that these effects are caused mechanically…

There are different kinds of urticating hairs and all of them appear exclusively in the New World tarantulas.The hairs of contact (type II), big and heavy, which the spider does not throw but places approximating its abdomen, only appear in arboreal tarantulas (that in Uruguay we do not have). There are other kinds of hair which are light, small and can be transported by the air (types I, III, IV and VI). The evolution of these hairs has been rather puzzling, cause two different types of hair could have been present in just one spider, what would suggest that these hairs have had a common origin. In the figures we show you a scheme of the evolution of most of the genus of the American tarantulas, where the different types of urticating hairs which they present have been traced.

The figures that follow are cladograms that represent probable genealogies of the genera of the New World tarantulas. In blue you can see the genus with different types of urticating hairs.      





Excepting the men, tarantulas have few enemies. Vertebrates seem to dislike them, perhaps because of their respectable size, poisonous chelicerae and their fearsome urticating hairs, capable of frightening even the most courageous. It must be like eating a cactus! Only one case has been reported in Uruguay:a young tarantula in a bird’s stomach (a ‘bandurria’ or plumbeous ibis, relative to the cuervillo or ibis and the pink spoonbill). However, there is an enemy for whom the hairs are not a barrier and the size of the spider is an incentive: the great pompilid wasp of the Pepsis genus.



The females of these wasps are able to immobilize big spiders two, three or more times bigger than themselves, by using their strong poison of the sting that they have at the end of the abdomen. The strong spines at the legs of the wasp prevent them from receiving the hug of the spider, while the sting is thrusted repeatedly into the softer sides of the spider, in the articulations of the coxae and sternum. If the spider manages to bite the wasp, the last one has a very hard armour that generally resists from the attacks of the chelicerae. 



If a wasp hunts a spider on the surface of the ground –as an example, if the wasp hunts a male- it will need to construct a cave for burying the prey. Sorry, we have forgotten to tell you: the prey is not for being eaten. Moreover, the wasp drinks  a few blood cause really it is a romantic that feeds on nectar. The prey is for the sons. The wasp will place only one egg on the lethargic spider –not dead- which will transform into a carnivore larva who will consume the whole spider in twenty days. Of course, this defenceless larva can’t eat her special dish at the open field. It will need a safe place. This place will be a capsule under the ground. That is why the wasp will dig a cave. Or it won’t … Much better it will be to take advantage of the cave of the spider and simply adapt a section and close it up.The larva will eat up the poor owner and will transform into a pupa that will hibernate until it comes out as an elegant hornet at the end of the following summer… 



But some species of tarantulas have find a solution. Eupalaestrus weijenberghi  has evoluted to construct a narrow tube at the end of the cave, where she entrenches and exposes the end of the abdomen to the invader wasp. The wasp is prevented from thrusting the sting in any vital place, so it gives up and withdraws.




Species of Uruguay 



G. iheringi

G. mollicoma sur

G. mollicoma norte

A. suina

E. weijenberghi

P. longisternale

H. uruguayense

O. argentinense


The big Grammostola

Climbed at the rocky hilly zones and gorges all over the country, hidden under the big stones, the gramostolas, the biggest spiders of Uruguay and among the biggest of the world, have their caves. Two species are known. One of them, the biggest, lives in the ‘Quebrada de los Cuervos’, at the province of Treinta y Tres, and is called Grammostola iheringi . The other species is distributed all over the country and is called Grammostola mollicoma. This species has an odd characteristic: in general, the populations of the north of the ‘Río Negro’ (a river that divides our country in two) are black, while the ones of the south are brown. We are still trying to elucidate whether they are really one species with two subspecies, or two different species. What we are sure about is that under laboratory conditions they copulate freely with each other. The males wander looking for females, specially at the beginning of the summer.

This is G. iheringi, male and female. Small differences with the other species (compare them) are visible when they are alive: the presence of a silver fluff on the cephalotorax, longer nails on the legs and specially a very calling spot of urticating hairs, with the shape of an apple. It can be endemic of this region in Uruguay and for this reason: SHOULD NOT BE COLLECTED because we could be driving the species to extinction.

This is G. mollicoma (from the north). It is black (or if it is brown, of a very dark brown). Some of the hairs that cover the body have a whitish end. It will never present red hairs as the ones of the south. The spot of urticating hairs is diffused. It is more agile than the one of the south, what can be confirmed comparing the speed when capturing preys.

This is G. mollicoma (from the south).  It is brown, somehow lighter when the skin is old and it is about to moult. It shows reddish hair (like Shakira… when reddish), specially on the lateral sides of the legs. We have detected the local extinction of this species at the ‘Cerro de Montevideo’, an environment with strong pressure. As you can see, they are vulnerable animals.



The medium-sized


Capriciously, almost despotically, here we group three different genera, just because of their size. Is it clear?


This is Acanthoscurria suina. Light brown, strong and short, she is Gardel’s friend (see front page). It lives at the grasslands and hilly zones of the south of Uruguay, where she digs caves with a final chamber. With Eupalaestrus weijenberghi (see later on), she is an active consumer of the beetle Diloboderus abderus, whose larva ‘the isoca’, is an important plague for the pastures. It bites a lot and threatens elevating the front legs and opening the chelicerae and showing the drops of poison. However, its bite is not dangerous but it hurts (if you want to know how much, ask our friend Carlos Toscano).

This is Eupalaestrus weijenberghi. Longer and darker than Acanthoscurria, with two light bands on the articulations. The females and juveniles have the cephalotorax and the first three pairs of legs lighter colour than the abdomen and the last pair of legs. For threatening, this tarantula elevates the abdomen (look at the photograph). As Acanthoscurria, it lives in caves but only at the grasslands. The tubular cave has a neck, a chamber and a narrow-end tube, that is used to protect itself from the enemies, specially the big wasps. Together with Acanthoscurria, males go out in March or April (the end of summer and beginning of autumn here at the south). Usually, they go out in hot and wet days, when it is about to rain.



This is Plesiopelma longisternale. Smaller than the other mediums. Black, but with abundant reddish hair at the beginning of the abdomen, as a punk star. It is an ‘ all conditions’ spider as the Acanthoscurria suina: it lives both at the hilly zones as well as at the open land. At the grasslands, it constructs simple caves with a lot of silk at the entrance, while at the hilly zones it stays under stones, and in general it does not dig and covers the shelter with abundant silk. When the individuals are small, they are normally confused with Homeomma uruguayense.  



The small ones


This is the short Homeomma uruguayense. Looking similar to a Plesiopelma but shorter and with punk hair, but not so calling. It lives in hills all over the country, under very, but very buried stones. The caves are deep and almost always closed. We do not know how does it get in and out from there. Costa supposes that it eats termites. Different from the other tarantulas, males of this species wander around during the winter, probably to evade predation.


Olygoxystre argentinense. This one is very different from the rest. It is the only tarantula from Uruguay which has not got urticating hairs or cuspules on the labium. Why? It is a faraway relative of the others: this is (Hold on!) a Ischnocolinae, while the rest are Theraphosinae… Subfamily matters…

Its body is longer than the rest and it is much quicker with its movements. Good climber (she was born to become a politician). It is frequent to find it  between  stones in rocky areas, and she almost never constructs caves. It is  the only tarantula which makes a fixed disk-shaped eggsac.


Exclusive for tarantula fans


How can we identify the ‘bird spiders’ of Uruguay?


In general, all of them are big and hairy. But we have already seen that not all of them are so big and it is also true that there are some hairy spiders that are not bird spiders. To identify strictly a tarantula (Theraphosidae family) of Uruguay, the spider has to fulfil, altogether, the following three requirements:


1) Having parallel chelicerae

2) Having a brush of hairs (scopula) on the ventral side of the last segment of the legs (tarsi).

3) Possessing dense haired claw tufts under the claws of the legs. 




Guide for identifying species


To recognize the different species you will have to make a very careful observation of some parts and structures of the spider. Sometimes, this is only possible with dead or anaesthetized spiders, but with practice some parts can be seen with the living animal (be careful with your fingers…). It is very useful to use a powerful magnifying glass or, in some cases, a simple microscope. With the males it is very useful to observe the copulating bulbs of the palps. With the females or juveniles it is more difficult and in some cases the best thing to do is extracting some urticating hairs and observing them under the microscope. For extracting the urticating hairs from a living spider, you will have to soak with a thin layer of glycerine or saliva, a small area of the stage of the microscope and then you will need to contact that stage with urticating hairs on the abdomen of the spider. Later, remember that you should not take your fingers to your tongue without cleaning them first…

What comes next is the key, with two possibilities on each step, like a path which bifurcates (dichotomic key). Each possibility excludes the other one and finally you get to a species or to the number of the next step. We should point out that this key is useful principally for adult animals and, as all keys, you have just a few facts to consider (so it is not perfect at all). It is advisable to consider, additionally, the biological information indicated above for each species.


1.- If the spider is medium-sized, thin and fast, and has not got neither labial cuspules nor urticating hairs, it is an Oligoxystre argentinense. The males of this species have a bulb with a thin and long style and the females have thin and flattened egg-sacs.

--- If it has not got what is mentioned in 1, go to number 2.

2.- If the spider is medium-sized and has urticating hairs type I and III, go to 3.


--- If the spider has urticating hairs type IV and III, go to 4.


3.- If it is a female and is homogeneously light chestnut coloured or if it is a male (darker) and has the bulb like a corkscrew, it is an Acanthoscurria suina.

--- If it is a female and has the cephalothorax and the three front legs of a light chestnut colour and the fourth pair of legs and the abdomen of dark chestnut coloured (on the abdomen there are some hairs, longer and of a lighter colour than on other parts of the body), and if it is a male and it is dark and has the bulb like in the figure, it is an Eupalaestrus weijenberghi

4.- If it is big (more than 5 cm of body length), is dark chestnut coloured with reddish hair on the  legs when it is captured at the south of the ‘Río Negro’ (or dark brown coloured without reddish  hair when it is captured at the north), then it is a Grammostola mollicoma. Males have the bulb like the one in the figure.             

Note: A similar species to this one but somewhat bigger, with iridescent hairs on the back of the cephalothorax and until now only found in Uruguay at the ‘Quebrada de los Cuervos’ (‘Treinta y Tres’ province) is Grammostola iheringi.


--- If it is smaller, with less than 4 cm of body length, fly to number 5.

5.- If it is a dark chestnut coloured female, with reddish hairs (longer at the abdomen) and with abundant silk at the entrance of the cave, or if it is a male with a bulb like the one of the figure, then it is a Plesiopelma longisternale.   

--- If it is a light chestnut coloured female, with lighter bands on the articulations, which lives on a small cave with few silk under buried stones, or if it is a male and has the bulb like the one of the figure, it is a Homoeomma uruguayense.



There are lots of things that people believe and repeat about these spiders, that contribute to their bad reputation and are not true. That the bite is not dangerous, we have already told you and we will not insist on this!


The tarantulas DO NOT JUMP; they will not jump to your neck. They can move quickly and impress, especially a frightened person, but they will never jump much. For sure, this myth is inspired in the salticids, that can jump considerable distances. Taking this into account, we could possibly consider the tarantulas high-jump champions (if small spiders can jump so much, imagine the big ones…) but this is not correct. Among other things, for jumping you need good vision (you need to know where to fall) and these spiders have a very deficient vision. That is why, they nearly do not jump (have we said this before?). 

Tarantulas neither construct webs for capturing and much less, giant aerial geometrical webs like the ones that some horror films show (‘Arachnophobia’ and others). Although some spider webs are quite resistant, the tarantulas are too heavy for them. Moreover, just a few families of spiders construct geometrical webs for capturing. The poor tarantulas are only capable of covering their caves with some silk; females can delicately wrap up their small eggs into their egg-sac (can you remember?) and the males can make a dense sheet for the sperm induction … But hanging in the wind… never!


In some American countries they are made responsible for illnesses on the legs of the cattle, specially the horses: supposedly, these would be caused by tarantula bites (from there the name ‘horse stingers’). Really, these illnesses are infectious and have nothing to do with the poor tarantulas, that are not interested in biting a one-hundred-kilos animal which they are not going to eat.


In Uruguay, there is an extended belief about spiders that always go out in couples: ‘if one appears, the other one must be near’, they say. Tarantulas, as well as most spiders, are solitary animals. Females and males only get together for mating, during the reproductive period. Later, females and males live their own lives (that, as we have already seen, in these spiders is very, very different).


Faraway from here, the Yanomami from Brazil and Venezuela capture big tarantulas, burn their hair (the one of the spiders; they are brave but no fools!), and eat them. Rather than motivated by hunger, this is a rite based on the belief - very extended for some ethnic groups – that after eating the spider you will acquire the virtues of the animal. In this case, the giant Theraphosa blondii, the biggest of the world. As a kind of initiation for the young hunters, they have to test their courage: they must take one of these animals from its cave, wrap it up alive with a palm leaf and transport it to the village for the curious  ‘barbecue’.


Amazonic aborigine – very similar to Fernando Pérez-Miles- tasting the flavour of a Theraphosa blondii.