A keeper's journey 1: New World, Old World : myths and misconceptions
If you recently got your first tarantula, are in the process of doing your research prior to getting one (an essential step!), or are simply a spider enthusiast revolving around hobbyist spheres and watching content from spider keepers, you certainly have stumbled upon the notion of Old World/New World tarantulas before (and if not, you definitely will).
If you have heard about it in any further depth than just a mention of it, you probably know that it is a criterion hobbyists use to classify tarantula species in terms of disposition and venom potency: "Old World" species are for experienced keepers, because of their defensive disposition and medically significant venom, while "New World" species have a more docile temperament and milder venom, and are therefore more suitable for beginner keepers. Simple, convenient, but a tad simplistic.
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| According to their reputation, New World species (like Davus pentaloris) are rather docile and don't have medically significant venom, making them suitable for beginner keepers |
Because it is most often thrown around by and for beginner tarantula enthusiasts, who do not know spiders very well yet, and do not necessarily understand the full picture of this New World/Old World thing, it is frequently distorted and extrapolated, so much it has given birth to numerous myths.
Among the most common examples of these myths, we find the NW/OW labels being meaninglessly applied to spiders which are not tarantulas, some species from the American continent being labelled "Old World", the incorrect assumption that all Old World tarantulas have medically significant venom, that all NW tarantulas are suitable for beginners, or even all OW tarantulas being described as hyper-aggressive monsters that will jump at you and bite at the slightest provocation.
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| Old World tarantulas, such as Pterinochilus murinus (the "orange baboon tarantula") are infamous for their spicy attitude and potent venom, to a degree that often far exceeds reality |
Let's see what this New World/Old World divide is really about, where it applies and, most importantly, where the "rule" finds its limits.
Meaning and origin
The denominations "New World" and "Old World" are terms that are originally borrowed from history and geography, in contexts that have nothing to do with spiders. Historically, it refers to dates at which Europeans became aware of the other continents around them. Africa and Asia have been on European maps (and trading routes) since the Antiquity, so these three continents, connected by land and inhabited by populations who have known about each other for thousands of years, form the Old World.
Meanwhile, because America and Oceania were not reached by Europeans until centuries later, they form the "New World" of Eurocentric history.
However, this distinction is not just relevant to historians and geographers. The "New World" has been isolated from the "Old World" by two major oceans for millions of years (except for the periodically emerged land bridge between Siberia and Alaska, which only existed during very cold periods, only allowing mammals, birds and cold-hardy plants to cross it, and not impacting much of the other living groups), which means life on the American continent has evolved in isolation for a long time, becoming markedly different from biodiversity found in Eurasia and Africa, where species from each continent are typically more closely related due to the existence of permanent land bridges.
Thus, the concepts of Old World and New World are also relevant to biogeography¹, albeit with one notable difference: while Oceania, the last continent to be reached by Europeans, is part of the New World according to its historical definition, biogeography treats it as part of the Old World, as its biodiversity, although quite unique, shows more similarities with the rest of the latter than with the Americas.
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| The Old and New World according to biogeography: basically a distinction between the Eastern and Western Hemispheres |
What it means for tarantulas
Like many other living groups in the area, Theraphosidae (tarantulas) in South America (it is almost certain that the Caribbean, Central and North America were colonised by tarantulas originating from South America) have evolved in isolation from their Old World counterparts for something like 50 million years.
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| The vast majority of New World tarantulas, including this Chromatopelma cyaneopubescens, belong in the subfamily Theraphosinae |
As all the major New World tarantula subfamilies (except Ischnocolinae and one weird lineage, represented by the strange genus Catumiri, which may have a very different history) are closely related, it is largely assumed they all evolved from one common ancestor that colonised South America (possibly from Asia) somewhere between 70 and 50 million years ago.
At some point of their evolution, New World tarantulas developed a fascinating defensive apparatus: urticating setae (setae = "hairs"; the fuzz which covers insects and spiders isn't actually hairs, as they're completely different from what mammals have, which is why scientists call them "setae" instead).
Because of their very large average size compared to most spiders, Theraphosidae occupy a fairly special place in the food chain. They have access to a wide range of prey, including large invertebrates and small vertebrates, but are also targeted by an a slightly different guild of predators compared to other spiders. For average-sized spiders, the vast majority of predators are Arthropods, like other spiders, wasps, centipedes, scorpions and large carnivorous insects, as well as small vertebrates such as frogs, lizards, small mammals and songbirds.
While they also fall prey (particularly as spiderlings and small juveniles) to these typical spider predators, adult tarantulas are large enough to catch the attention of truly formidable foes: medium-sized to large mammals. Mongoose, meerkats, coatis, raccoons, opossums, hedgehogs, rodents, small monkeys, baboons and even humans (yes, some human populations in Asia and South America routinely consume tarantulas) are significant predators of Theraphosidae.
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| Foraging baboons are relentless; they'll leave no stone unturned. While plants form the bulk of their diet, Arthropods, including tarantulas, make up about 10% of their menu |
The thing is, most spiders aren't particularly well-equipped to defend themselves against predators much larger than their own size. All they have is their venom, which is primarily a hunting weapon; producing that venom is costly in terms of energy, and using it for defence is a waste of a resource that should normally be invested in obtaining a meal. On top of that, it can only be delivered through a bite, which means the spider has to get dangerously close to its foe, putting itself at high risk of getting injured or killed. That's why all spiders (yes, including Old World tarantulas and "bogeymen" species such as Loxosceles and Phoneutria) are reluctant to bite defensively, and will only do so as a very last resort.
With their urticating setae, New World tarantulas won the great lottery of evolution. In fact, it is such a great advantage that Theraphosinae, the subfamily most proficient in its use of these irritating hairs, is, by far, the most diverse of the family.
Urticating setae represent a simple, energy-efficient defence mechanism, which, unlike venom, can be used to repel large predators from a safe distance.
They simply consist in modified setae ("hairs") forming a patch on the abdomen. Unlike the setae that cover the rest of the body, urticating "hairs" are brittle and detach easily when the spider rubs its back legs against them.
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| Urticating setae form a patch on the abdomen that has a slightly different sheen or colour; particularly visible on spiderlings (as the dark patch contrasts with their pale body) this patch can differ in shape from one genus to another, aiding identification |
These urticating hairs don't contain any venom or toxin; their effect is purely mechanical, caused by their peculiar shape. Observation with a powerful microscope reveals these tiny setae are barbed, with shapes reminiscent of harpoons (there are seven different types with different shapes; different genera/species have different types or combination of types).
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| The seven known types of urticating setae found in New World tarantulas (from Kaderka et al, 2020) |
When a NW tarantula kicks its urticating setae, they detach from the abdomen and become airborne, forming a cloud around the spider. When they hit soft tissue such as skin or mucous lining, they become embedded, and, because of their shape, are very hard to dislodge, irritating the tissue around them.
Because they have a lot of fragile, exposed skin and mucous, particularly on the face, mammals are especially vulnerable to urticating setae; to a lesser extent, they also work on other vertebrates such as birds and lizards, though they have to hit the eyes or the lining of the mouth.
Upon contact, these setae cause immediate burning pain, particularly if they hit the more sensitive areas like the nose and eyes. A vertebrate predator hit by these hairs will back off immediately, and will think twice before putting its face near a tarantula again.
Thus, New World tarantulas are equipped with an effective, low-risk, low-energy defensive weapon against mammals, which many use liberally, rather than trying to bite.
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| Urticating setae detach easily when the tarantula kicks them; specimens under frequent stress, particularly skittish, or about to moult can kick to a point where their abdomen becomes almost completely bald (they're renewed every time the spider moults, like normal setae) |
Old World tarantulas aren't so lucky. The odds of random genetic mutation never gave them anything as efficient as urticating setae, which means they have to protect themselves the old-fashioned way, using camouflage, speed and, when all else fails, their venom, to avoid predation .
Because they don't go through the extra step of kicking hair, an Old World tarantula, confronted and cornered by an animal much larger than itself, will promptly adopt a defensive stance, legs outstretched and fangs on display, and, if that's not enough for the predator to back off, may resort to biting.
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| Often misinterpreted as the "agressive pose" of a spider that "wants to bite", this defensive display actually aims at the exact opposite: its purpose is to repel the assailant without having to resort to wasting venom in a defensive bite. |
Because they have a much better option than biting to defend themselves from mammalian predators, the venom of New World tarantulas equipped with urticating hairs has mostly evolved as a hunting weapon, against prey that are mainly Arthropods. Thus, the venom of New World tarantulas doesn't contain loads of toxins active on mammals, and its effects on large mammals are rather limited.
Old World tarantulas, on the other hand, need their venom for hunting, but also for defence against mammals. Thus, many are armed with toxins (or have greater concentrations of these toxins in their venom than NW species) active on mammals. Their venoms generally have more marked effects on them than NW tarantula venoms, particularly when it comes to pain and muscle cramping (after all, the intended purpose is to deter the predator, not kill it).
In the broad lines, the New World/Old world distinction is mostly true: the latter generally have a more potent venom on mammals (including humans) and can inflict more serious bites than the former, while also often being more prone to defend themselves this way.
For tarantulas only
The three subfamilies of New World tarantulas equipped with urticating setae are the only spiders, out of the 139 currently recognised families of the order, to possess them. This unique evolutionary innovation is what drives the difference in medical significance to humans between most NW and most OW Theraphosidae species.
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| The difference in medical significance between Old World and New World species only exists in the family Theraphosidae, i.e. tarantulas (and it has exceptions) |
That means this OW/NW divide regarding medical significance of venom is only applicable to tarantulas and makes no sense when applied to any other spider family.
For all other spider families, the meaning of "Old World" and "New World" is exclusively about origin. Some families are only found in the Old World, some only in the New World, and many in both.
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| The strange family Xenoctenidae is exclusively found in the New World |
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| The family Phyxelididae, on the other hand, only occurs in the Old World. |
For all these other families, their origin does not say anything about their medical significance. Remember that, because the vast majority of other spiders are much, much smaller, on average, than Theraphosidae, they are not targeted by the same guilds of predators at all.
Defence against vertebrates, especially mammals, has therefore not been a major driver in the evolution of most spider families, Old or New World. Thus, on both hemispheres, the picture is pretty much the same: a very small minority of medically significant species, while the vast majority of spiders isn't.
When it comes to these medically significant species, no hemisphere really has it worse than the other; the proportion of medically significant species is about the same on either side of the Atlantic Ocean.
A trend, not a rule!
Evolutionary trends should never be understood as rules; they're the result of permanent, gradual change, so you rarely, if ever, find hard lines and unbroken laws in nature. Thus, the Old World/New World "rule of thumb" unsurprisingly has exceptions on both sides.
First, not all New World tarantulas have urticating hairs.
Out of the six main New World lineages (subfamilies Theraphosinae, Psalmopoeinae, Aviculariinae, Schismatothelinae, Ischnocolinae and the confusing genus Catumiri), only three, Theraphosinae, Aviculariinae and part of Psalmopoeinae, are equipped with urticating hairs.
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| While they are a New World subfamily, Schismatothelinae, which includes Neoholothele incei, do not possess urticating hairs |
Psalmopoeinae are an interesting case as, out of the four currently recognised genera (Amazonius, Ephebopus, Psalmopoeus and Tapinauchenius), only Ephebopus, which also happens to be the only non-arboreal genus, has urticating setae. It is unclear whether the other genera did have them but lost them at some point of their evolution, or if Ephebopus acquired them independently from the other subfamilies that possess urticating hair. To make things even more confusing, the urticating hair of Ephebopus are not on the abdomen, but on the pedipalps!
All other Psalmopeinae are entirely devoid of urticating hairs, anywhere on their body.
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| Species of the genus Psalmopoeus are the most famous example of a New World genus without urticating hairs, but they're far from the only ones |
In fact, it is only because the vast majority of New World species belong to the highly diverse subfamily Theraphosinae, which includes something like 590 species (i.e. almost half of the entire family's diversity) that this conflation between New World species and the possession of urticating hairs is mostly true.
The idea that Old World species have more potent venom is a bit of an overgeneralisation as well. While it is true that, because they only have their speed and their venom to defend themselves, they are all very fast and generally tend to have a more potent venom to mammals than NW species, not all of them are considered medically significant to humans.
Old World Ischnocolinae such as Ischnocolus, Chaetopelma or Heterothele, all relatively small but very fast tarantulas, are not known to be medically significant.
Similarly, while the genus Pterinochilus (at least the species P. murinus, and likely other species of the genus as well) is medically significant, other genera of the subfamily Harpactirinae such as Harpactira, Harpactirella, Ceratogyrus, Eucratoscelus or Idiothele, are not considered medically significant in their native African range, and not feared by local people (unlike Stromatopelminae, whose bites are notorious and feared among local populations).
Interestingly, bites by Australian Selenocosmiinae (chiefly Selenocosmia, and the species formerly included in Phlogiellus, now Coremiocnemis, Selenotypus and Selenotholus) only cause relatively mild effects on humans, with a low prevalence of muscle spasms, comparable to New World species, while they are highly toxic and frequently fatal to dogs. This is definitely something to consider if you're thinking about keeping one of these species and have a pet dog, but it also shows how variable the effects of a venom can be from one species to another, even among mammals.
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| While they are often assumed, alongside all Old World species, to be medically significant by people in the hobby, most Harpactirinae are not regarded as such in their native range |
What it means for keepers
Old World tarantulas only have their speed, intimidating displays and venom to defend themselves. They are much faster than beginner-friendly New World species, and often move in explosive, unpredictable bolts. This can make them more difficult to manage, particularly in tense situations like rehousing or escapes, which is why they're best suited for the more experienced keepers, who know tarantulas enough to anticipate these sudden bursts of speed and deal with them calmly.
As the effects of their bites are also, generally, more severe, and as they can be quicker to resort to biting than more laid-back NW species, they leave a much smaller margin for error.
That's why it is strongly advised to build experience with more docile New World species, then with faster ones, before moving into keeping Old World species.
However, this reality has resulted in quite a lot of exaggeration and blanket statements about OW species, and how dangerous they actually are to their keepers. In another article, we discussed the extreme and somewhat undeserved demonisation of Pterinochilus murinus, the OBT, but most Old World species are often depicted in a similarly negative light (albeit to an often lesser extent than P. murinus). Both their defensiveness and their venom are frequently overblown to a point where it borders on scaremongering.
While it is true that they're often less forgiving than "docile" New World species, they are not monsters, and a calm, experienced keeper who treats them with the respect they deserve will have no issues. On top of that, we've seen that not all OW species are actually considered medically significant, and some species, while still fast, tend to be relatively calm and seldom defensive.
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| Although closely related to the infamous OBT, Pterinochilus lugardi is a relatively calm Old World species, that rarely reacts defensively |
While this fuss over Old World species is needlessly scary, it has, at least, the merit of keeping some inexperienced keepers away from species they wouldn't be ready for.
Much more harmful, in my opinion, is the excessive complacency with which many keepers treat New World tarantulas. It is not uncommon to see keepers, mainly the less experienced ones, handling NW tarantulas, especially the "beginner-friendly" ones of the genera Aphonopelma, Grammostola, Brachypelma and Tliltocatl, and playing with them carelessly as if the risk of a bite was zero.
It is unfortunately no surprise, then, that the genus that ranks second among the most implicated in bites on keepers is no other than the "docile", "beginner-friendly" Grammostola.
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| While Grammostola is one of the most frequently recommended genera for beginner keepers, it ranks second in number of bites by captive tarantulas! |
Of course, this worrisome statistic is not caused by the spider's attitude itself (as most Grammostola are indeed generally laid-back), but by how complacent people are with them. Keepers do things with these "beginner" tarantulas they'd never attempt with more high-strung species, forgetting that even a normally slow-moving and docile spider can move fast and react defensively if it perceives itself as threatened.
These sudden reactions often come off as a much bigger surprise than with more defensive species, which means the keeper is often less prepared for them, and doesn't deal with them as smoothly.
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| Even docile, beginner-friendly species are occasionally capable of unpredictable reactions |
Sure, their venom won't require medical attention in case of bite, but that doesn't mean it won't be a painful and scary experience. Big tarantulas have very large fangs, manoeuvred by powerful muscles.
In the largest species, such as those of the genera Theraphosa, Lasiodora or Pamphobeteus, these fangs can reach 2 cm long in adult females, and are often over 1 cm long in adult females of species that range between 15 and 20 cm in legspan (a size category that includes a lot of larger NW and OW species).
Although they won't always sink their fangs all the way in when biting defensively, a bite from a large tarantula can be a deep and painful wound, even without considering the presence of venom.
Such an experience can be quite traumatic to a keeper, particularly a beginner, and cause them to become scared of their pet, or even put them off keeping tarantulas entirely.
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| The fangs of a female Theraphosa spp., the largest of all tarantulas, can reach 2 cm in length, and are manoeuvred by muscles powerful enough to crush a mouse's skull |
Tarantulas, including NW beginner species, are not toys, nor are they domesticated animals that seek human contact. As solitary creatures and mid-size predators that can fall prey to lots of larger animals, they see us, at best, as a neutral part of their environment (like we perceive a tree or a hill), and at worst as a threat, depending on how we interact with them. Just because docile species have a higher tolerance threshold doesn't mean they'll never react defensively. All tarantulas are wild animals with wild instincts, which need to be understood as such, and treated with respect.
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| When aggravated enough, even a species as docile as everyone's favourite beginner tarantula, Tliltocatl albopilosus, can react defensively. Some specimens are also more high-strung than others (which is the case of this one) |
On top of that, stereotyping all New World tarantulas as slower, docile and "beginner-friendly" can result in some startling surprises.
NW species that don't possess urticating hair, such as those in the subfamilies Psalmopoeinae and Schismatothelinae, compensate this lack of primary defences with their dazzling speed. This being said, the rumour that some of them, notably Psalmopoeus irminia, have medically significant venom, is unsubstantiated. The symptoms of the single bite case this claim is based on are consistent with an allergic reaction (as is the response to epinephrine) rather than the direct effects of the venom; the other known Psalmopoeus bite records are local to mild envenomations, comparable in severity to other New World species.
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| Psalmopoeus species and other Psalmopoeinae are extremely fast, agile, and can jump |
Even among the genera equipped with urticating hairs, slow and docile isn't exactly a norm. Many Theraphosinae species, particularly the large, relatively long-legged "birdeaters" in the genera Phormictopus, Theraphosa, Pamphobeteus, Xenesthis, Megaphobema or Nhandu, are actually skittish, very fast and reactive spiders, which will be quick to defend themselves by kicking hair, rearing up and slapping the ground when they perceive a threat, and will not hesitate to bite if further aggravated. They are also extremely food responsive, and will sometimes fiercely attack something they mistake for potential prey... In terms of attitude, these fast, high-strung New World species are just as reactive, if not more, than your average Old World tarantula.
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| Although they are a New World genus equipped with urticating hairs, species of the genus Phormictopus are fast and notoriously high-strung, and can be just as cantankerous as Old World species |
Yet, perhaps the most problematic of all the misconceptions about New World species is how much people in the hobby tend to downplay urticating hairs.
Tarantula bites and their effects draw a lot of attention and concern, while the hairs are often treated as a mere inconvenience. They can, however, have rather serious consequences, and shouldn't be taken lightly.
On the skin, their effects can vary depending on the species, on the person (some people are much more sensitive than others), and on the area of skin where they get embedded. They range from itching, pain and rashes, to painful blisters and extensive skin irritation, sometimes persisting for weeks, for the most irritating types. Many keepers also report a sensitivity that builds up over time, with reactions becoming more severe after years of exposure.
Yet, it's when they get embedded in the cornea of the eye that these hairs can turn from an inconvenience to a medical emergency. Even a single hair in the eye can cause conjunctivitis, keratitis (inflammation of the cornea) or even, if it is not removed rapidly, uveitis (when the tissues underneath, such as the iris and its muscles, become inflamed). These affections are serious, require urgent medical care, and can result in long-term damage to the eye and degradation of vision if left untreated. Treatment, in the least severe cases, will consist in topical steroids and antibiotics, but surgical corneal debridement is necessary for the trickier ones.
Urticating setae, especially the particularly potent type III, notably found in Brachypelma, Lasiodora, Theraphosa, Grammostola or Chromatopelma, are therefore just as medically significant, if not more, than a bite, when they enter the eye.
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| The urticating hairs from Lasiodora species are known to be especially potent |
It is also important to keep in mind that species that possess urticating hairs are often much more prone to using them than any tarantula, New or Old World, tends to use its venom defensively.
As species equipped with these hairs will also sprinkle them around and onto themselves when moulting, even moults and webbing must be handled with care, as moving them can be enough to send a cloud of hair off into the air.
When keeping tarantulas, the risk of being exposed to urticating hairs is therefore much greater than the risk of ever being bitten by one.
While it is true that many New World species, such as those from the genera Brachypelma, Tliltocatl, Aphonopelma, Grammostola or Lasiodora, are more suitable for beginner keepers as they aren't as fast and less likely to bite than Old World species, they are still capable of defending themselves in ways that can have serious consequences on human health.
As often in biology, it is easy to misunderstand the evolutionary trend that distinguishes Old and New World tarantulas as a rule, and misinterpret it.
Not all Old World tarantulas are medically significant, and not all New World species are beginner-friendly. Old World tarantulas are not monsters, and New World tarantulas aren't toys. Docile doesn't mean harmless. Urticating hairs are not something that can be overlooked or shrugged off as a mere inconvenience.
While tarantula keeping is a completely safe activity for a careful, respectful and informed keeper, these animals, Old or New World, are not cuddly pets one should handle and play with.
Tarantulas are "non-domestic" pets, meaning that they remain wild animals even in captivity, which don't need to be feared, but have to be treated with respect and caution, regardless of their origin.
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| No tarantula is a monster, but they all need to be treated with respect |
Glossary
¹Biogeography: The discipline of biology that studies the geographical ranges of extant and fossil living species and their evolution, as well as the factors influencing that evolution.
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