Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae .[2] As of December 2023, 1,100 species have been identified, with 166 genera.[3] The term “tarantula” is usually used to describe members of the family Theraphosidae, although many other members of the same infraorder (Mygalomorphae) are commonly referred to as “tarantulas” or “false tarantulas”. Some of the more common species have become popular in the exotic pet trade. Many New World species kept as pets have setae known as urticating hairs that can cause irritation to the skin, and in extreme cases, cause damage to the eyes.[4]
Like all arthropods, the tarantula is an invertebrate that relies on an exoskeleton for muscular support.[5] Like other Arachnida, a tarantula’s body comprises two main parts, the prosoma (or cephalothorax) and the opisthosoma (or abdomen). The prosoma and opisthosoma are connected by the pedicel, or pregenital somite. This waist-like connecting piece is actually part of the prosoma and gives the opisthosoma a wide range of motion relative to the prosoma.
Depending on the species, the body length of tarantulas ranges from about 5 to 11 cm (2 to 4+1⁄2 in)[6] with leg spans of 8–30 cm (3–12 in).[citation needed] Leg span is determined by measuring from the tip of the back leg to the tip of the front leg on the opposite side. Some of the largest species of tarantula may weigh over 85 g (3 oz); the largest of all, the goliath birdeater (Theraphosa blondi) from Venezuela and Brazil, has been reported to attain a weight of 170 g (6 oz)[7] and a leg-span up to 30 cm (12 in), males being longer and females greater in girth. The fang size of this tarantula reaches a maximum of 4 cm (1+1⁄2 in).[7]
Theraphosa apophysis (the pinkfoot goliath) was described 187 years after the goliath birdeater, so its characteristics are not as well attested. T. blondi is generally thought to be the heaviest tarantula, and T. apophysis has the greatest leg span. Two other species, Lasiodora parahybana (the Brazilian salmon birdeater) and Lasiodora klugi , rival the size of the two goliath spiders.
Most species of North American tarantulas are brown. Elsewhere, species have been found that variously display cobalt blue (Cyriopagopus lividus), black with white stripes (Aphonopelma seemanni), yellow leg markings (Eupalaestrus campestratus), metallic blue legs with vibrant orange abdomen and green prosoma (Chromatopelma cyaneopubescens). Their natural habitats include savanna, grassland such as in the pampas, rainforest, desert, scrubland, mountains, and cloud forest. They are generally classed among the terrestrial types. They are burrowers that live in the ground.
Tarantulas are becoming increasingly popular as pets and some species are readily available in captivity.
Identification
Tarantulas can be confused with other members of the order Mygalomorphae, such as trapdoor spiders, funnel-web spiders and purseweb spiders. They can also be confused with some members of the order Araneomorphae such as the Lycosidae family. There are multiple ways to identify a tarantula. First the hairs: in the Americas most tarantulas have urticating hairs, though some, such as the Hemirrhagus genus, lack these. The hairs are usually more noticeable than with most other spiders. Another is the size, as tarantulas tend to be bigger, but this is again not a failproof way. They also do not use their webs for hunting, instead using them as building material or tripwire.[8]
One of the most decisive ways to tell is by looking at their fangs. Tarantula fangs face downwards, as opposed to those of true spiders, which face each other, allowing them to make pincerlike motions. They also own two book lungs, as opposed to true spiders which only have one. Their lifespan is also longer than most spiders.[8]
Etymology
The spider originally bearing the name tarantula was Lycosa tarantula, a species of wolf spider native to Mediterranean Europe.[9] The name is derived from the southern Italian town of Taranto.[10] The term tarantula was subsequently applied to almost any large, unfamiliar species of ground-dwelling spider, in particular to the Mygalomorphae and especially the New World Theraphosidae. Compared to tarantulas, wolf spiders are not particularly large or hairy, and so among English speakers in particular, usage eventually shifted in favour of the Theraphosidae, even though they are not closely related to wolf spiders at all, being in a different infraorder.
The name tarantula is also incorrectly applied to other large-bodied spiders, including the purseweb spiders or atypical tarantulas, the funnel-webs (Dipluridae and Hexathelidae), and the dwarf tarantulas. These spiders are related to tarantulas (all being mygalomorphs) but fall into different families from them. Huntsman spiders of the family Sparassidae have also been termed tarantulas because of their large size, when, in fact, they are not related. Instead, huntsman spiders belong to the infraorder Araneomorphae.
The element pelma in genus names
Many theraphosid genera have names, either accepted or synonymous, containing the element pelma. This can be traced back to Carl Ludwig Koch in 1850,[11] who in describing his new genus Eurypelma wrote, “Die Sammetbürste der Fussohlen sehr breit” (lit. ‘the velvet-brush of the footsole very wide’).[12] German arachnologists use the word Fuß to refer to the tarsus (the last article of a spider’s leg).[13] Translations of Sammetbürste into Latin use the word scopula.[14] Hence in English arachnological terminology, Koch meant ‘the scopula of the base of the tarsus very wide’. Eury- is derived from the Greek eurýs (εὐρύϛ), meaning ‘wide’, while pélma (πέλμα) means ‘the sole of the foot’,[11] paralleling Koch’s use of Fußsohle (in modern spelling). Thus Eurypelma literally means ‘wide footsole’; however, arachnologists have conventionally taken pelma in such names to refer to the scopula, so producing the meaning ‘with a wide scopula’.[11]
Other genus names or synonyms that Estrada-Alvarez and Cameron regard as having ‘footsole’ or ‘scopula’ meanings include:[11]
- Acanthopelma – Greek ácantha (ἄκανθα) ‘thorn, spine’; overall meaning ‘spiny footsole’
- Brachypelma – Greek brachýs (βραχύϛ) ‘short’; overall meaning ‘short scopula’
- Metriopelma – Greek métrios (μέτριοϛ) ‘of moderate size’; overall meaning ‘medium length scopula’
- Schizopelma – from the Greek origin combining form schizo- (σχίζω) ‘split’; overall meaning ‘split footsole’
- Sericopelma – Greek sericós (σηρικόϛ) ‘silky’; overall meaning ‘silken scopula’
Later, particularly following genus names published by R.I. Pocock in 1901,[15] the element pelma appears to have become synonymous with ‘theraphosid’. For example, the author of Cardiopelma writes, “Cardiopelma fait réference aux genitalia de la femelle qui évoquent la forme d’un Coeur” (‘Cardiopelma refers to the female genitalia that evoke the shape of a heart’), with no reference to either ‘footsole’ or ‘scopula’. Names interpreted in this way include:[11]
- Aphonopelma – Greek áphonos (ἄφωνοϛ) ‘soundless’; overall meaning ‘theraphosid without sound’
- Cardiopelma – Greek cardía (καρδία) ‘heart’; overall meaning ‘heart theraphosid’ (referring to the heart-shaped female genitalia)
- Clavopelma – Latin clavis ‘club’; overall meaning ‘theraphosid with club-shaped hairs’
- Delopelma – Greek delós (δηλόϛ) ‘clear, obvious, visible, conspicuous, plain’; overall meaning ‘theraphosid without plumose hair’
- Gosipelma – the element gosi- means ‘desert’, relating to the Gosiute people; overall meaning ‘desert theraphosid’
- Spelopelma – Greek spélaion (σπήλαιον) ‘cave’; overall meaning ‘cave theraphosid’
- Distribution
Tarantulas of various species occur throughout the United States, Mexico, in Central America, and throughout South America. Other species occur variously throughout Africa, much of Asia (including the Ryukyu Islands in southern Japan), and all of Australia. In Europe, some species occur in Spain, Portugal, Turkey, southern Italy, and Cyprus.
Habits
Some genera of tarantulas hunt prey primarily in trees; others hunt on or near the ground. All tarantulas can produce silk; while arboreal species typically reside in a silken “tube tent”, terrestrial species line their burrows with silk to stabilize the burrow wall and facilitate climbing up and down. Tarantulas mainly eat large insects and other arthropods such as centipedes, millipedes, and other spiders, using ambush as their primary method of prey capture. Armed with their massive, powerful chelicerae tipped with long, chitinous fangs, tarantulas are well-adapted to killing other large arthropods. The biggest tarantulas sometimes kill and consume small vertebrates such as lizards, mice, bats, birds, and small snakes.
The eight legs, the two chelicerae with their fangs, and the pedipalps are attached to the prosoma. The chelicerae are two double-segmented appendages located just below the eyes and directly forward of the mouth. The chelicerae contain the venom glands that vent through the fangs. The fangs are hollow extensions of the chelicerae that inject venom into prey or animals that the tarantula bites in defense, and they are also used to masticate. These fangs are articulated so that they can extend downward and outward in preparation to bite or can fold back toward the chelicerae as a pocket knife blade folds back into its handle. The chelicerae of a tarantula completely contain the venom glands and the muscles that surround them, and can cause the venom to be forcefully injected into prey.
The pedipalpi are two six-segmented appendages connected to the prosoma near the mouth and protruding on either side of both chelicerae. In most species of tarantulas, the pedipalpi contain sharp, jagged plates used to cut and crush food often called the coxae or maxillae. As with other spiders, the terminal portions of the pedipalpi of males function as part of their reproductive system. Male spiders spin a silken platform (sperm web) on the ground onto which they release semen from glands in their opisthosoma. Then they insert their pedipalps into the semen, absorb the semen into the pedipalps, and later insert the pedipalps (one at a time) into the reproductive organ of the female, which is located in her abdomen. The terminal segments of the pedipalps of male tarantulas are moderately larger in circumference than those of a female tarantula. Male tarantulas have special spinnerets surrounding the genital opening. Silk for the sperm web of the tarantula is exuded from these special spinnerets
A tarantula has four pairs of legs and two additional pairs of appendages. Each leg has seven segments, which from the prosoma out are: coxa, trochanter, femur, patella, tibia, tarsus and pretarsus, and claw. Two or three retractable claws at the end of each leg are used to grip surfaces for climbing. Also on the end of each leg, surrounding the claws, is a group of bristles, called the scopula, which help the tarantula to grip better when climbing surfaces such as glass. The fifth pair is the pedipalps, which aid in feeling, gripping prey, and mating in the case of a mature male. The sixth pair of appendages is the chelicerae and their attached fangs. When walking, a tarantula’s first and third legs on one side move at the same time as the second and fourth legs on the other side of its body. The muscles in a tarantula’s legs cause the legs to bend at the joints, but to extend a leg, the tarantula increases the pressure of haemolymph entering the leg.
Tarantulas, like almost all other spiders, have their primary spinnerets at the end of the opisthosoma. Unlike most spider species in the infraorder Araneomorphae, which includes the majority of extant spider species, and most of which have six, tarantula species have two or four spinnerets. Spinnerets are flexible, tube-like structures from which the spider exudes its silk. The tip of each spinneret is called the spinning field. Each spinning field is covered by as many as 100 spinning tubes through which silk is exuded. As the silk is pulled out of the spinnerets, the shear forces cause proteins in the silk to crystallize, transforming it from a liquid to a solid thread.
The tarantula’s mouth is located under its chelicerae on the lower front part of its prosoma. The mouth is a short, straw-shaped opening that can only suck, meaning that anything taken into it must be in liquid form. Prey with large amounts of solid parts, such as mice, must be crushed and ground up or predigested, which is accomplished by coating the prey with digestive juices secreted from openings in the chelicerae.
The tarantula’s digestive organ (stomach) is a tube that runs the length of its body. In the prosoma, this tube is wider and forms the sucking stomach. When the sucking stomach’s powerful muscles contract, the stomach is increased in cross-section, creating a strong sucking action that permits the tarantula to suck its liquefied prey up through the mouth and into the intestines. Once the liquefied food enters the intestines, it is broken down into particles small enough to pass through the intestine walls into the hemolymph (blood stream), where it is distributed throughout the body. After feeding, the leftovers are formed into a small ball by the tarantula and thrown away. In a terrarium, they often put them into the same corner.[16]
Nervous system
A tarantula’s central nervous system (brain) is located in the bottom of the inner prosoma. A tarantula perceives its surroundings primarily via sensory organs called setae (bristles or spines, sometimes referred to as hairs). Although a tarantula has eight eyes like most spiders, touch is its keenest sense, and in hunting, it primarily depends on vibrations given off by the movements of its prey. A tarantula’s setae are very sensitive organs and are used to sense chemical signatures, vibrations, wind direction, and possibly even sound. Tarantulas are also very responsive to the presence of certain chemicals such as pheromones.
The eyes are located above the chelicerae on the forward part of the prosoma. They are small and usually set in two rows of four. Most tarantulas are not able to see much more than light, darkness, and motion. Arboreal tarantulas generally have better vision compared with terrestrial tarantulas.
Respiratory system
All types of tarantulas have two sets of book lungs (breathing organs); the first pair is located in a cavity inside the lower front part of the abdomen near where the abdomen connects to the cephalothorax, and the second pair is slightly farther back on the abdomen. Air enters the cavity through a tiny slit on each side of and near the front of the abdomen. Each lung consists of 15 or more thin sheets of folded tissue arranged like the pages of a book. These sheets of tissue are supplied by blood vessels. As air enters each lung, oxygen is taken into the blood stream through the blood vessels in the lungs. Needed moisture may also be absorbed from humid air by these organs.
A tarantula’s blood is unique (not only in appearance); an oxygen-transporting protein is present (the copper-based hemocyanin), but not enclosed in blood cells such as the erythrocytes of mammals. A tarantula’s blood is not true blood, but rather a liquid called hemolymph (or haemolymph). At least four types of hemocytes, or hemolymph cells, are known.
The tarantula’s heart is a long, slender tube located along the top of the opisthosoma. The heart is neurogenic as opposed to myogenic, so nerve cells instead of muscle cells initiate and coordinate the heart. It pumps hemolymph to all parts of the body through open passages often referred to as sinuses, and not through a circular system of blood vessels. If the exoskeleton is breached, loss of hemolymph will kill the spider unless the wound is small enough that the hemolymph can dry and close it.
Predators
Despite their large size and fearsome appearance and reputation, tarantulas themselves are prey for many other animals. The most specialized of these predators are large members of the wasp family Pompilidae such as the wasp Hemipepsis ustulata. These wasps are called “tarantula hawks”. The largest tarantula hawks, such as those in the genus Pepsis, track, attack, and kill large tarantulas. They use olfaction to find the lair of a tarantula. The wasp must deliver a sting to the underside of the spider’s cephalothorax, exploiting the thin membrane between the basal leg segments. This paralyzes the spider, and the wasp then drags it back into its burrow before depositing an egg on the prey’s abdomen. The wasp then seals the spider in its burrow and flies off to search for more hosts. The wasp egg hatches into a larva and feeds on the spider’s inessential parts, and as it approaches pupation, it consumes the remainder.[17] Other arthropods, such as large scorpions and giant centipedes, are also known to prey on tarantulas.[18]
Tarantulas are also preyed upon by a wide variety of vertebrates. Many of these, including lizards, frogs, birds, snakes and mammals, are generalist predators of all kinds of large arthropods. Mammals that have been known to prey on tarantulas, such as the coati, kinkajou, and opossum in the New World, and mongooses and the honey badger in the Old World, are often immune to the venom of their arthropod prey.
Humans also consume tarantulas for food in their native ranges. They are considered a delicacy in certain cultures (e.g. Venezuela[19] and Cambodia). They can be roasted over an open fire to remove the bristles (described further below) and then eaten.
Tarantulas have evolved specialized bristles, or setae, to defend themselves against predators. Besides the normal bristles covering the body, some tarantulas also have a dense covering of irritating bristles called urticating hairs, on the opisthosoma, that they sometimes use as protection against enemies.[20] These bristles are present on most New World species, but not on any specimens from the Old World. Urticating hairs are usually kicked off the abdomen by the tarantula, but some may simply rub the abdomen against the target, like the genus Avicularia. These fine bristles are barbed and serve to irritate. They can be lethal to small animals such as rodents. Some people are sensitive to these bristles, and develop serious itching and rashes at the site. Exposure of the eyes and respiratory system to urticating hairs should be strictly avoided. Species with urticating hairs can kick these bristles off; they are flicked into the air at a target using their back pairs of legs. Tarantulas also use these bristles for other purposes, such as to mark territory or to line their shelters (the latter such practice may discourage flies from feeding on the spiderlings). Urticating hairs do not grow back, but are replaced with each molt. The intensity, number, and flotation of the bristles depends on the species of tarantula.
To predators and other enemies, these bristles can range from being lethal to simply being a deterrent. With humans, they can cause irritation to eyes, nose, and skin, and more dangerously, the lungs and airways, if inhaled. The symptoms range from species to species, from person to person, from a burning itch to a minor rash. In some cases, tarantula bristles have caused permanent damage to human eyes.[4]
Some setae are used to stridulate, which makes a hissing sound. These bristles are usually found on the chelicerae. Stridulation seems to be more common in Old World species.