The Find-a-Spider Guide

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Glossary of Terms

NOTE: To see each illustration more clearly click on it to produce an enlarged version

Click to enlarge Abdomen: The second of the two main parts of the body of a spider. It is usually soft and easily damaged although on some species it is at least partly protected by tough 'shell-like' dorsal and/or ventral scutes. It is connected to the cephalothorax by a thin pedicel.

Click to enlarge Araneomorph spiders: The more advanced spider families, often called the modern spiders, most of which can survive in webs or other open environments without suffering rapid desiccation. Araneomorphs usually have only two book lungs on the underside of their abdomens and their fangs operate in a transverse pincer fashion.

Click to enlarge Book lungs: Small pocket-like openings on the underside of the abdomen. The advanced (araneomorph) spider families have one of these on each side of the abdomen close to its front end but primitive spiders (mygalomorphs) have a second pair behind the first.

Click to enlarge Calamistrum: A uniform comb of stiff hairs on the second last segment of the fourth pair of legs of just a few spider families. It is used to comb silk from the web-spinning cribellum of those spiders that produce lacy cribellate webs.

Click to enlarge Carapace: The relatively hard upper 'shell' of the cephalothorax, which is the front part of a spider. Just in front of it is a head (or caput) region that contains the spider's eyes. In its centre the carapace usually has a groove called the fovea, which has a variable shape and orientation and hence has some taxonomic usefulness.

Click to enlarge Cephalothorax: The first of the two main parts of the body of a spider. This part has the chelicerae with fangs attached, the pair of palps and the four pairs of legs attached to it.. Inside it are some muscles, a sucking stomach and most of the nervous system.

Click to enlarge Chelicerae: A pair of short appendages at the front end of a spider. The fangs are attached to the outer end of these structures, which in mygalomorphs contain the spider's venom glands as well. The orientation of the pair of fangs and the way they interact are of value for determining the family to which the spider belongs. Typically, mygalomorph fangs operate vertically and in parallel whereas on araneomorphs they move transversely in a pincer action.

Click to enlarge Claw tuft: A thick brush-like set of hairs at the end of the legs of some spiders. When present these are always paired and are located just behind the tarsal claws. They are not the same as the bundle of ordinary hairs that are at the ends of the legs of many spiders.

Click to enlarge Compression bandage: An elastic bandage that is wrapped around a limb over a bite site with sufficient tension to slow, but not stop, the flow of blood through the site. Its usual purpose is to impede the flow of venom-containing blood into the general circulation.

Click to enlarge Cribellum: A flat plate-like structure projecting backwards from the underside of the female abdomen of some spiders and used as a source of silk instead of one pair of spinnerets. In some families the silk-secreting part of this plate is divided into left and right halves.

Click to enlarge Diaxial fangs: A pair of fangs that operate transversely in pincer fashion. This arrangement is found on araneomorph spiders. To ensure that the fangs can penetrate deeply the chelicerae of most kinds of araneomorph spiders can open out to quite a wide angle.

Click to enlarge Egg sac: A container or wad of spider silk that may contain and protect several hundred eggs until they hatch. Egg sacs can be round or pillow-shaped and sometimes have projections around their edges that perhaps are used to anchor them in place.

Click to enlarge Envenomation: Poisoning following the injection of a spider's venom into the skin. The components of spider venoms that are most toxic to humans and other vertebrate animals are small neurotoxic peptides, but in most spiders insecticidal toxins are more important. These do little harm in humans.

Click to enlarge Epigastric furrow: A groove across the underside of the abdomen that marks the rear edge of the book lungs and the point of entry into the female genitalia.

Click to enlarge Epigynum: The hardened, external mating structure found centrally on the underside of the abdomen of a female spider just in front of the epigastric furrow. It is easily seen on fully mature araneomorphs but not on mygalomorphs or immature araneomorphs.

Click to enlarge Eye patterns: The set of four (or sometimes fewer) pairs of eyes found on the caput, which is the somewhat raised front upper end of the cephalothorax just behind the fangs. These eyes are often arranged in two rows of four so we refer to the front ones as the anterior median and lateral eyes (AME and ALE) and the rear ones as the posterior median and lateral eyes (PME and PLE).

Click to enlarge Fangs: These are tapered and curved needles attached to the ends of the chelicerae and used by a spider to inject its venom into a victim. They are hollow and are attached to venom glands located in the chelicerae of mygalomorphs or inside the cephalothorax of araneomorphs.

Click to enlarge Fovea: a short groove visible in the centre of the upper surface of the carapace. This may be straight or curved and may run lengthwise or across the carapace. On some species it appears to be entirely missing.

Click to enlarge Instar: An immature form of a spider. In general, instars have some resemblance to the adult female but they tend to have different markings and their genitalia do not have a mature external appearance, if they are visible at all.

Click to enlarge Leg segments: An immature form of a spider. In general, instars have some resemblance to the adult female but they tend to have different markings and their genitalia do not have a mature external appearance, if they are visible at all.

Click to enlarge Moulting: When an immature spider breaks out of its body skin to grow larger. This is the only way spiders can increase in size as they mature to adulthood. Most spider species pass through several instar sizes before becoming adults and some long-lived mygalomorph females are said to moult occasionally even after becoming adults.

Click to enlarge Mygalomorph spiders: The so-called primitive spider families which usually die quickly from desiccation unless they can hide in a moist burrow. For this reason the males are mostly only active and outside the burrow at night and during rainy periods and the females spend almost all of their time in their burrows. Mygalomorphs have two pairs of book lungs and fangs that are almost parallel and strike vertically.

Click to enlarge Necrotising arachnidism: Progressive ulceration and loss of skin around the site of a biting allegedly caused by a number of araneomorph spider species. Note that there is only one Australian genus, Loxosceles, which is has been proven to have this adverse effect on humans and it is very rare. The actual cause of the necrotizing phenomenon is uncertain and for this reason no fully effective treatments for it are available in Australia at the present time.

Click to enlarge Neurotoxin: A nerve poison which is present in the venom of most spiders and is used to immobilise prey. Only a small number of spider species have neurotoxins potent enough to be life-threatening to humans but most spiders have venom components that paralyse their normal prey, which typically includes insects and other spiders.

Click to enlarge Palps: Also called pedipalps, these are short, leg-like structures attached to the front of the cephalothorax between the fangs and the first pair of conventional legs. In females and in immature males they resemble small legs, although they have one less segment. In mature (or sometimes nearly mature) males the terminal segments are modified into a bulb and needle that are used for mating.

Click to enlarge Paraxial fangs: A pair of fangs that strike downwards in parallel arcs. This is the normal arrangement on a mygalomorph spider. In this case the chelicerae do not open up much but the spider is able to get good penetration into its prey by first elevating the front of its body using its first two pairs of legs.

Click to enlarge Scopula: A dense brush-like mat hairs on the underside of the terminal segments of at least some legs on certain spider species. these hairs give the spider better traction, especially on relatively smooth surfaces.

Click to enlarge Sexual dimorphism: This term is used when the male and female of the same spider species have physical characteristics so different that they appear to be different species. This is most obvious when the spiders are mature and it is often impossible to determine the sex of an immature spider just by looking at its surface anatomy.

Click to enlarge Spinnerets: These are the web-spinning organs found on the underside of the abdomen at or near its rear end. There are at least two pairs present and sometimes three but often one pair are notably larger than the others. The orientation of the set of spinnerets and the length and pattern of silk-extruding spigots on each spinneret are sometimes important for identification purposes.

Click to enlarge Spur: A sharp thorn-like projection from a segment of a leg. Spurs are much thicker and more tapering than the hairs found on the legs of many spiders. Depending in their overall appearance some spurs may instead be called megaspines.

Click to enlarge Tarsal bulb: The expanded end segment of the palps of a mature male spider. This more-or-less spherical bulb has a hollow needle (often coiled) called the embolus projecting from it. These structures are essentially the metatarsus (sixth leg segment) which stores and transfers sperms during mating. The tarsus (here called the cymbium) is attached to one side of these structures.

Click to enlarge Tarsal claws: A pair of small claws at the end of each leg, used by the spider to hold onto objects, including its own web. Many species have a smaller median claw behind the main pair, which are equal in size except on spiders belonging in the Family Gradungulidae, where one claw is much larger than the other. The purpose of this large claw is unclear.

Click to enlarge Tibia: The fifth segment of a spider's leg, counting outwards from the cephalothorax. On males it often carries spines or spurs, this being particularly true for the first or second tibia which are frequently important for protecting the male during mating.


Email Ron Atkinson for more information.    Last updated 21 April 2015.