Introduction

Immature male specimen of Theraphosa stirmi, also known as the Burgundy Goliath Birdeater

The Tarantulas are a large group of primitive spiders belonging to the taxonomic family Theraphosidae, with this group containing a wide array of species with varying form, colour and behaviour. They also belong to the Mygalomorphae infra-order, with this group often being very long lived, with female specimens of some species having a lifespan of up to 25 years in captivity, as opposed to around 2-3 years for the Araneomorph, or typical, spiders and are often much larger and heavier bodied.

The Taranulas were first named after a species of wolf spider found in Italy, the European Wolf Spider, which was also referred to as the Lycosa tarantula. This name was originally derived from a local belief that the bite from this relatively harmless spider could only be cured by a dance, called the Tarantella, and the name spread to be used for all large, hairy spiders. Nowadays the name Tarantula is only really applied to members of the family mentioned before, with a large array of species now being found in captivity.

All Tarantulas are active predators, with their diet primarily consisting of insects and other invertebrates, but some of the larger species will also actively predate upon small mammals, reptiles and amphibians. This group also generally have limited food requirements, as their inactive lifestyle tends to make them very efficient, with captive specimens often being fed either weekly, in the case of younger or more active species, or bi-weekly, in the case of most adult specimens of the more commonly kept grammostola and Brachypelma species, but will often fast for long periods of time until they feel they require food again.

The simple needs of this group make them ideal candidates for captivity, as they do not require a large space, require very limited feeding and often thrive in the environmental conditions provided in the home, with some species only requiring a small heat-mat or an occasional spray to suit their needs. This part of the website should hopefully outline the basics of tarantula biology and taxonomy alongside a generic care guide, outlining the basics of tarantula care, but for a lot of species more specific information should be examined.

Biology

Introduction

This section will give a brief introduction to the general anatomy and biology of tarantulas, with a focus on interesting facts and information relevant to the care of this group in captivity. This section will also hopefully outline the key differences between this family and other groups of spiders, with the focus being on the biological differences between the araneomorph and mygalomorph spiders and their behaviours.

External Anatomy

The tarantula family shares a lot in common in terms of their basic anatomy with other spiders, but the predominant features of the body are the cephalothorax, which is akin to a combined head and thorax, and the abdomen. The eight legs are attached to the cephalothorax, with the pedipalps, the smaller appendages at the front of the body, and the chelicera, the two projections at the front with the fangs protruding from underneath, being at the front of the cephalothorax to allow for capturing prey. The feature that attaches the abdomen to the cephalothorax is termed the pedicel, and is a small piece of flexible skin that allows for movement of the abdomen without the whole body moving.

Tarantulas possess a pair of spinnerets at the rear end of the abdomen, used to produce the silk that the spider produces to line burrows and the tank, with these being smaller of larger in certain species due to differences in the amount of web required by the behaviour of the species. Within this group the two pairs of book-lungs are located at the bottom of the abdomen either side of the vent, which is the small line near the front of the bottom of the abdomen, and houses the reproductive organs.

The legs are often divided into sections, and the tarantulas possess an ability to remove damaged limbs from the base, and will often regenerate these throughout successive moulting. The coxa is present at the base of the leg, and houses the “valve” that the spider can use to remove the leg. The next section is the trochanter, with this section being where the leg will break when removed, but also allows for a larger degree of motion.

The next section of the leg is the femur, which is a larger section, and is followed by the patella, which acts to increase the range of motion by providing the flexibility required to extend the leg. The tibia is the next section, and is analogous to our shin, and is followed by the beginning of a section that is analogous to the ankle and foot of the tarantula. The first part of this section is the metatarsus, which acts to provide a “hinge” for the foot to position itself in a way that allows for traction. The foot of the tarantula is composed of the tarsus, which acts as a pad with a layer of incredibly fine hairs, which allow the tarantula tremendous grip on substances such as glass by increasing the surface area to a point where the van der waals interaction and friction between the pad and the surface vastly increase traction.

Anther external feature are the eyes, with tarantulas possessing eight simple ocelli. Sense in tarantulas is usually dominated by the sensory hairs present over the body, with these being used to detect movement around the spider, and are extremely sensitive. The eyes are thought to be primarily used for detection of light level changes. The eyes in tarantulas are located in a cluster near the front of the carapace, and are often slightly raised.

Internal Anatomy

The internal anatomy is slightly more complex, but a key feature of the spider Is the fovea. This is the dip (or horn in some species) present at the top of the carapace, and acts as a point of muscle attachment for movement of the legs. Another predominant feature that borders between internal and external is the is the mouth of the tarantula, with tarantulas only being able to take in food in liquid form. This is achieved through the secretion of digestive enzymes from the mouth onto captured prey and partly through action of the venom, with the spider first liquefying prey and then ingesting it using a sucking stomach, with muscles anchored to the fovea, which is located near the front of the internal cavity of the cephalothorax.

This leads to the digestive tract, which processes the food ingested, with waste being secreted in the form of a white paste. Tarantula faeces is often seen as a white chalky substance when dry, but this is normal for this group as they will often deposit it around the tank. After feeding the indigestible parts of the prey will be left in a small bundle, often termed a food bolus. Other features of the internal anatomy include the interior surfaces of the book lungs, which act as a gas exchange surface, and the internalised genitalia. The abdomen also houses the remainder of the digestive tract and the apparatus used to produce eggs in females.

Moulting

An important part of the tarantula lifecycle is moulting, which involves shedding the old exoskeleton to allow for growth. This process is started with the formation of a new exoskeleton underneath the old one, and can often be seen by a darkening in colour associated with behavioural changes, and tarantulas undergoing this process will often stop eating until they moult. The spider will usually moult upside down, and will split the carapace from the top of the cephalothorax and slowly pulse its body to remove the old exoskeleton. This process is often extremely stressful, and the spider should be left alone during this time. After moulting is complete the spider should take around a week or two for the new exoskeleton to darken, and during this time will be very vulnerable, and as such food should not be offered until the fangs have turned black, which indicates the exoskeleton has sclerotized.

Hunting

Tarantulas are predators, with their prey predominantly being invertebrate but will willingly take mammalian, reptilian and amphibian animals, with some of the larger species being able to feed on carrion from animals such as birds. It is interesting that the Goliath Birdeater (Theraphosa Spp.) obtained its name from a print in the 1800’s depicting a member of this genus consuming a bird. This is most likely rare in nature, and the spiders will most likely not actively hunt birds but will instead consume them if found.

Tarantulas hunt using their fangs, with the chelicera housing venom glands that are used to produce the venom for hunting and defence. The venom produced by this group is not often medically significant for humans but will quickly kill the prey taken, although some old-world species can cause severe reactions, such as members of the Poecilotheria genus, and as such care should be taken and the species you keep should be heavily researched to avoid incidents. Mammalian prey will be taken, but is often in the form of smaller species from groups such as the rodents. Tarantulas will often feed on carrion, with the young spiders often being raised on parts of deceased insects.

Determing The Sex of a Tarantula

Determining the sex of a tarantula is often more complex than with other animals, as spiders possess internalised reproductive organs. Two predominant methods exist for determining the sex, although a mature male is often conspicuous, as explained below, with these methods being examining the shed exoskeleton of the spider or through ventral sexing. Examining the shed exoskeleton is often the most accurate method, as it involves looking for the presence or absence of the pouch females use to receive sperm from the male between the book lungs on the interior of the abdomen, and requires the least specialised knowledge, and I recommend this method over others.

To utilise this method, you will need to have a moult from the spider, and while it is still pliable spread the abdomen, which should be split down the sides, flat so that you can see the interior surface and examine between the first pair of book lungs. Female spiders will possess a small, often conspicuous pouch here, called a spermathecae, with the size and shape being determined by the species. Male spiders will usually have either a tiny fold of skin present on the vent or nothing at all.

Ventral sexing tends to be more difficult, and should often be left to experienced keepers or the accuracy can be reduced, but involves looking at the base of the abdomen for a specialised patch of glands just above the vent, called the epiandrous fusillae, with these being used to produce the specialised web utilised by males during mating. Females will not have these hairs present, but will often have a slightly more enlarged vent, although these differences can be very small in certain species.

Sexual dimorphism can be very pronounced in certain species, but often only presents in the fact that males are often a significant degree smaller than females, and will only show external traits in a lot of species when they reach maturity, whereas females will keep the same body form throughout their lifespan. Mature males possess modified pedipalps and in certain species will have tibial hooks, a pair of hooks on the front pair of legs utilised for holding the females fangs out of the way while mating. Mature males will produce what is termed a sperm web, within which they will use specialised organs to produce a web containing sperm and will use this to load the specialised emboli on the end of the pedipalps, and after this he is ready for breeding.

Breeding

Mating should be attempted after the female is freshly moulted and has hardened, as moulting will remove the spermathecal lining and therefore the sperm stored. Tarantula mating involves introducing a mature male to the female’s enclosure, with care being taken that the female does not consume the male as often happens if the mating is unsuccessful when the male is introduced or can happen during mating. The male can be removed from the enclosure using a small net or such if this happens or they can be separated using some sort of tool, such as a piece of plastic.

Mating is often rapid in tarantulas, but the build-up can take time, with some degree of cohabitation usually being required beforehand. Mating in tarantulas often involves the male drumming his legs around the entrance to the females burrow or near her, to give the message that he is a male, with the female then often approaching. The male will then attempt to insert the emboli, the modified parts holding the sperm on mature male’s pedipalps, into the females vent. This will then allow him to deposit the sperm, and mating should be finished.

After mating the male should be removed, and the female given as stress free an environment as possible and should be offered food frequently, and within the next few months the abdomen will grow larger and she should produce an egg sack. Whether or not to pull the egg sack is controversial, as they are prone to mould and with improper husbandry, the female can eat the egg sack. I would recommend leaving the egg sack with the female, and if the husbandry is correct, the eggs should develop properly. When the clutch begins to darken they should be removed from the tank and put into a tank suitable for housing small spiders, with the young often being left together for their first few moults, and should be separated after they start to grow to between one and two centimetres.

Taxonomy

The tarantulas comprise of an entire family of spiders, with around a thousand known species with more being classified all the time. The taxonomy of this group has often been contested, and is always changing, but it is generally accepted that there are 35 subfamilies within this group. The main division however is between the new and old world species, with new world species being from the American continent and the old-world species being native to areas such as Africa and Asia. The new world species tend to be the least aggressive, with a key difference being that the venom of new world tarantulas is often weaker and they possess a covering of urticating hair on the abdomen, that can be used to deter predators. The old-world tarantulas do not possess these hairs but are often slightly more defensive and have more potent venom.

Notation of species includes the common name, and the binomial name including the genus and species. Identification of species can be difficult, but for more specific knowledge about the individual groups please see our species list.

Basic Care

The more commonly kept species of tarantula are often some of the easiest and most low maintenance of the exotic animals currently kept in the UK, and if some basic rules are followed should thrive in your care. An ideal set up for a tarantula should emulate the natural requirements of the species as closely as possible, to minimise stress for the animal, with more specific care guides for some of the more commonly kept species being found in their entry in the species list on this site.

Tank Design

The first part of the tank design for these animals that should be considered is the tank itself, and should ideally be secure, well ventilated and around two to three times the length of the tarantulas leg-span, to allow room for movement, but should ideally be as large as possible. Another consideration should be the height of the tank, with arboreal species requiring the tank to be higher than it is wide, as they will utilise the height, with terrestrial and fossorial species requiring a tank that prioritises floor space over height, and if you can’t determine which type of set up your tarantula requires you should check the species list for the more commonly kept species.

I highly recommend the use of Really Useful Boxes, commonly abbreviated as RUB’s, with either ventilation holes or mesh fitted to the top of the tank, but in most cases, any form of appropriately sized, clear plastic tank can be modified to house a tarantula. Glass aquariums can also be modified for use in this way, although the lid must be secure and well ventilated. Several products specifically designed for this purpose also exist, with brands such as exo-terra and zoomed having excellent products, such as faunariums, designed for this purpose.

Substrate

The second consideration should be the substrate used in the tank, which will have implications for both the comfort of the animal and will influence the environmental conditions within the tank due to factors such as the water retention of the substrate. In most cases, some form of coconut coir, a substrate commonly utilised within the exotic animal trade, is often a good choice, as this substrate resists mould, holds water well and can be used in either a dry or damp form.

Other substrates commonly used include peat and topsoil, with both being suitable but care should be taken with topsoil to ensure there are no chemical additives, as these substances may harm the animal. A factor that should be taken into account with a peat or some form of peat mix should be the fact that when allowed to dry the peat will often take a long period of time to absorb the water compared to coconut coir, and care should be taken with the species that require a slightly elevated humidity.

The substrate depth is another consideration, with a deeper layer of substrate holding more moisture and generally keeping the humidity more level while also allowing the spider to display more natural behaviour, such as burrowing in fossorial and terrestrial species. For most of the commonly kept terrestrial species a depth of around 2-3 inches should be used and for fossorial species a depth of around 4 inches should be used at a minimum, as these species will often form small burrows that they will occupy. For the arboreal species the substrate is not as much of a concern, but should still be provided at a depth of around 1.5-2 inches as a minimum, to provide a more natural environment and to minimise damage if the spider falls.

Furnishings

The third consideration should be the tank furnishings, with a basic, but appropriate, tank including a minimum of a hide and a water bowl, with fresh water being required to be on offer at all times, although with arboreal species the water bowl either needs to be raised or the side of the tank can be misted to provide droplets of water for the tarantula to utilise. The ideal water bowl should be clean and around three quarters of the leg-span of the spider, and also should be placed with the top slightly above the level of substrate, as this allows the spider to drink without increasing the risk of drowning.

The hides provided also differ between the ground dwelling terrestrial and fossorial species and the arboreal species, as arboreal species will not tend to utilise hides placed on the ground and prefer a piece of material, such as a few large pieces of cork bark, placed on the side of the tank. For the ground dwelling species a variety of material can be used, with a more natural aesthetic theme tending to lead to the use of cork bark or some form of flat wood and a more minimalist theme utilising objects such as a half-buried plant pot. Care should be taken to ensure that all tank fittings are secure, as movement could lead to falls, and this could lead to injury or death for the animal. The hide should ideally allow for the spider to go completely inside, as this will minimise light levels for the animal and allow for more natural behaviours.

Heating & Humidity

Supplemental heating for the tank should only really be utilised if the room drops below around 15-20 degrees Celsius consistently, as the more commonly kept species will often thrive at room temperature, although care should be taken to ensure the temperature is not too low all the time. If supplemental heating is required a heat mat should be attached firmly to a side of the tank, as tarantulas will often instinctively burrow if they become too warm, and in captivity if the heater is placed under the tank this could lead to injury for the spider. Supplemental humidity can be provided in the form of using a spray bottle full of clean water to gently mist the tank once or twice a day if required.

References

  1. Schultz, S.A. & Schultz, M.J.(2009) Tarantula Keeper's Guide, 2nd Edition. Barrons Educational Series, USA.
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