Abdomen: the hindmost section of the spider body, also called the opisthosoma. The heart, reproductive organs, respiratory organs, digestive tract, and silk spinning glands are all included inside the abdomen. This body segment is soft and expandable, unlike the rest of the spider’s hard exoskeleton.
Anterior: nearer to the front end; i.e. the eyes are anterior to the abdomen.
Arachnid: a member of the Class Arachnida. This includes spiders, ticks, mites, scorpions, and their kin. Spiders belong to the Order Araneae.
Arachnologist: one who studies the class Arachnida, which contains all the arachnids (spiders, scorpions, mites, ticks, opiliones, etc).
Araneologist: one who studies the order Araneae, which contains only the spiders.
Araneomorph: the “true spiders”; a more advanced spider who belongs to the Araneomorphae suborder of Araneae. About 93% of all spiders are araneomorphs. Orbweavers, Wolf Spiders, and Cobweb spiders are a few of the more commonly dealt with araneomorph families. Their chelicerae open like salad tongs, rather than opening forward as do those of mygalomorphs.
Autotomy: also called “autospasy”, this is the act of a spider voluntarily amputating, or dropping off, its own leg(s) in response to a dangerous situation in order to help free itself. Dangerous situations include being grabbed or caught by something, maybe a predator, as well as having a limb get stuck during the process of molting. For example, spiders often come into contact with bees and wasps and may get stung on the leg. Fortunately, the spiders’ leg(s) can be autotomized in a matter of seconds before the bee’s venom can spread into the spider’s body. Certain leg muscles automatically detach themselves at the point of weakness and pull back into the body, letting the leg fall off. Then other muscles act as a closing mechanism while the hemolymph pressure (blood pressure) forces the joint membrane to bulge forward, which succeeds in sealing the wound. If the spider still has molting to do, it will be able to grow that leg back, although it will be thinner and shorter than the rest of the legs. Some species have areas of specific weakness in each leg, which means autotomy will nearly always happen there first. For instance, spiders in the Pimoidae family have autotomy at the patella-tibia joint, but for the majority of other families, the autotomy happens closer to the body at the coxa-trochanter joint. Autotomy is fully controlled by the spider and will not happen while a spider is anesthetized. The willingness of a spider to drop its leg varies across families. Some are very touchy and will autotomize right away, like the Cellar Spiders and Running Crab Spiders. Tarantulas, Jumping Spiders, and Crab Spiders autotomize only as a last resort. Still others, like the Longjawed Orbweavers and the Metellina genus, will not autotomize under any circumstances.
Book lungs: the spiders’ respiratory organs. These are usually situated on the underside of the abdomen, towards the front. They look like hairless patches of cuticle. Underneath those hairless covers, there are “stacks” of hemolymph-filled cuticle. Via diffusion, air passes in between the layers of those “stacks” and allows the gas exchange to take place. Like humans, spiders take in oxygen and let out carbon dioxide. The arrangement of the “stacks” looks much like the pages of a book, hence the name, “book lung”. Book lungs are the original, or “primitive”, form of respiration in spiders. Some spiders have more advanced respiratory organs called tubular tracheae. Depending on the family or specific species, a spider can have both respiratory organs (one pair of book lungs AND one pair of tubular tracheae).
Carapace: the shield-like covering that protects the top of the cephalothorax.
Cardiac mark: a lanceolate (elongate) mark on the midline of the dorsal surface of the abdomen, over the heart. Also called the “heart mark.”
Catalepsy: a condition characterized by lack of response to external stimuli and by muscular rigidity; i.e. “playing dead.”
Cephalothorax: the forward-most section of the spider body, also called the prosoma. The head and the thorax combine to make this one segment. Pretty much the sensory center, this section contains the eyes, brain, venom glands, and stomach.
Chelicera: (pl: chelicerae) these are the mouthparts that are tipped with fangs; aka the jaws. In most species they open and close like a pair of salad tongs, while in others, like tarantulas and trap-door species, they move up and down in a stabbing motion. The fangs rest in a groove in the bottom of the chelicerae similar to blades in a pocket knife. Chelicerae are used for a variety of necessary tasks, like subduing prey and self-defense, but that‘s not all: trapdoor spiders use them to dig their borrows, nursery-web spiders for carrying egg sacs, orbweavers for transporting prey, and long-jawed orbweavers interlock their chelicerae during mating.
Cheliceral furrow: the groove at the end of the chelicera where the fang snugly fits like a blade in a pocket knife. When the spider bites, the fangs fold out from the furrow and penetrate the prey.
Chevron: a ‘V’ shaped pattern.
Coxa: (pl: coxae) the very first segment of the leg that is firmly attached to the cephalothorax. This segment is small and is the most visible from the underside of the spider or other arthropod. See also the entry for Legs & Leg Segments.
Cuticle: the stiff, chitinous protein that is the building material for the exoskeleton as well as other body parts. It consists of many layers, the strongest and thickest of which is the exocuticle. Please see “Exoskeleton” for adjoining information.
Distal: a directional term meaning away from the center, or away from the body. Example: the fingers are distal to the shoulder. Opposite meaning: proximal.
Diurnal: active in the daytime; occurring during the day.
Dorsal: the upper surface; towards the top.
Epigynum, Epigyne: (pl: epigyna) the complex region of female spiders covering the internal genitalia and located on the underside of the abdomen, near its connection to the cephalothorax. The epigyne area is the “finger print” to the species. More often than not, this area must be seen under a microscope by an experienced eye in order to determine the species.
Exoskeleton: the hard, external body shell of arthropods. It is made of a stiff material called the cuticle, which has many layers. The cuticle is the building material of the entire body surface, the joint membranes, tendons, apodemes, sensory hairs, and even the lining of the respiratory and reproductive organs. Apart from those structural functions, the cuticle also serves to protect the spider and prevents desiccation of its body. The soft abdomen can expand after a meal or for developing eggs because it is lacking the outermost, toughest layer of the cuticle called the exocuticle. The exoskeleton is strongest on the cephalothorax because it includes the endo-, meso-, and exocuticle, as well as a thin layer of epicuticle. This tough and non-pliable layering of cuticle is why spiders have to molt in order to grow.
Exuvia, Exuvium: (pl: exuviae) the leftover, shed exoskeleton after a spider, or other arthropod, has molted.
Eyes & Eye Arrangement: while most spiders have eight simple eyes, others can have only two, four, or six. Some cave dwelling species are even eyeless. The relative position of the eyes is very important for the systematic classification of spiders. Just by looking at the arrangement and relative sizes of the different eyes, an experienced person can often immediately determine the family a particular spider belongs to.
Family: a group of related plants or animals ranking in biological classification above a genus and below an order. The standardized suffix used to indicate family is “-idae”; e.g. Wolf Spiders belong to the Lycosidae family.
Fang: the terminal segment of the chelicera that has a duct leading to the venom gland. When not in use, it rests in the cheliceral furrow.
Femur: (pl: femora; femurs) the thigh; the 3rd leg or pedipalp segment between the trochanter and the patella. This is often the thickest segment. See also the entry for Legs & Leg Segments.
Geniculate: a term used to describe the knee-like form of some chelicerae. When the spider is viewed from above, geniculate chelicerae appear to bulge farther forward than the “face”. This can be easily seen in many species of Hacklemesh Weavers (Amaurobiidae family).
Genitalia: the external reproductive organs. For male spiders, these are the bulbs on the tip of the palps. For females, the epigyne area on the underside of the abdomen. Neither are fully developed and functional until adulthood.
Genus: (pl: genera) a category of biological classification that ranks between family and species and contains related species. The genus of a particular creature is the first word of the scientific name and should be capitalized and italicized (e.g. Steatoda grossa, where Steatoda is genus and grossa is species) .
Gravid: being swollen with eggs; pregnant.
Habitus: the general appearance, posture, or physical state of a living thing; in spider language, this is usually the view of the entire spider from above, without zooming in on any region in particular.
Heart mark: (see “cardiac mark”)
Hemolymph: a fluid in some invertebrates that functions like the blood in some vertebrates. The hemocyanin molecules in it are responsible for carrying oxygen throughout the spider’s body. It consists of a high water content, which is why spiders require water on a constant or recurring basis. The hemolymph works with a delicate hydraulic system to allow spiders to move their legs and chew and swallow their food, as well as many other things.
Immature: lacking complete development; not yet adult. This life stage for a spider means that the genitalia are not developed enough yet to even determine the gender of the specimen. This term is interchangeable with ‘juvenile’ or ‘sub-adult.’
Invertebrate: an animal without a backbone; often referred to as an “invert” for short.
Juvenile: (see “immature”)
Lateral: having to do with the side; i.e. a lateral view.
Legs & Leg Segments: all spiders are born with eight legs. The spiders’ hemolymph powered “hydraulic” system allows them to move and walk. Each leg is filled with nerves and covered with sensory receptors and sensory hairs. Spiders can test the chemical quality of the ground they walk on simply by probing it with the tips of their legs. Other chemical receptors on the tips of the legs measure the humidity of the air. Some receptors simply tell the spider what position it’s in. Every leg has seven segments: beginning closest to the body, coxa and then trochanter, which are both short; then a long femur and a knee-like patella; then a slender tibia and metatarsus; and last, at the very tip, is the tarsus which usually has two or three claws. (BODY=coxa–trochanter–femur–patella–tibia–metatarsus–tarsus=CLAWS)
Macro photography: taking extremely close-up pictures of subjects.
Mesothelae: the most primitive of the three suborders of Araneae. The spiders in this group have clearly segmented abdomens as well as other primitive features. The Liphistiidae family of Southeast Asia, China, and Japan is the only living family of this suborder. All other families are extinct and exist now only as fossils.
Metatarsus: (pl: metatarsi) the 6th segment of the leg, located between the tibia and the tarsus. This segment is lacking in pedipalps. See also the entry for Legs & Leg Segments.
Molt: (as a verb) triggered and controlled by hormones, this is the process of shedding the old exoskeleton. In all spiders there are three successive phases: (1) lifting of the carapace; (2) freeing of the abdomen; and (3) extraction of the extremities. Some larger spiders, like tarantulas, do this while laying on their back, while others do this while hanging from a silk thread. Experienced arachnologists can predict when a spider is going to molt: the spider withdraws and stops feeding, the legs get darker, and the abdomen seems to stretch and leave the pedicel more visible. The old exoskeleton is referred to as the “exuvia“, though some simply call it the “molt”.
Mygalomorph: a more primitive version of a spider that is typically heavy bodied and stout legged. About 15 families worldwide comprise this group. Tarantulas, as well as trapdoor and purseweb spiders, are included. Mygalomorphs belong to Mygalomorphae which is one of the three suborders of Araneae. The chelicerae (jaws) and fangs of mygalomorphs extend forward and then down in a stabbing motion instead of in a scissor-like motion as do the jaws of spiders in their larger sister suborder, the Araneomorphae.
Nearctic: relating to, or located in, the region of plant and animal life in the Arctic and temperate areas of Greenland and North America; the Nearctic Ecozone.
Nocturnal: active at night; occurring during the night.
Overwinter: to survive the winter. Spiders have adaptations that allow them to overcome cold, dampness, flooding, and lack of food. In part, they utilize leaflitter for extra insulation and also reduce their metabolic rate significantly. The winter-active spiders, such as those in the Linyphiidae family, keep warm by staying more active but they will die past -7 degrees Celsius. The spiders that are not winter-active are much more cold resistant. Some orbweaving species of Araneus can withstand temperatures of -20 degrees Celsius, even in unprotected areas. Some eggs overwinter inside the egg sac or cocoon and hatch in the Spring. Even heavy snowfall is no match for the spiders camping out in the leaflitter. The snow actually acts as insulation and keeps the temperature steady at around 0 degrees Celsius. So even in Canada where ambient air temperatures can reach -40 degrees Celsius, there is no effect on the spiders safe below the snow. The hemolymph of the spider contains glycerol, which acts as an antifreezing agent. During the winter, the glycerol levels are much higher. It is unlikely that the glycerol alone can create such strong cold resistance and this subject is still being studied.
Patella: (pl: patellae) the knee; the 4th segment of the leg or pedipalp located between the femur and the tibia. It is short and curved. See also the entry for Legs & Leg Segments.
Pedicel: the narrow stalk connecting the cephalothorax and the abdomen; the waist. There are 36 muscles contained within just this small area.
Pedipalps: also more commonly referred to as simply, the “palps”, these are the leg-like appendages on either side of the jaws, or chelicerae. They aren’t used for walking, but instead for manipulating food like an extra pair of hands. In adult male spiders, the tips of the pedipalps are large and have sperm storing organs that are used during copulation. Those male palps are sometimes referred to as “boxing gloves”, since that’s what they look like. During mating, the male palp is inserted into the female epigynum. Every palp has six segments (the same as the leg, except the metatarsus is lacking and the coxa is more often called the endite).
Penultimate: next to last; one molt shy of adulthood. The genitalia are partially formed and slightly visible. In males, the tips of the palps are smooth and swollen like boxing gloves. In females, there is a hardened and sometimes darkened area where the epigynum will soon be.
Posterior: nearer to the back end; i.e. the spinnerets are posterior to the eyes.
Proximal: this is a directional term meaning nearest to the center; nearest to the body. Example: the shoulder is proximal to the fingers. Opposite meaning: distal.
Pyriform: pear-shaped; often used to describe the shape of a spider’s carapace.
Scientific name: also called the binomial name, this is the combination of the genus and species of a creature. The combination is generally written in Latin or Latinized Greek and is accepted and understood worldwide, no matter what the language. These names are always subject to revision as more and more is understood about our spider friends. In text, the scientific name is always italicized and the genus is always capitalized (e.g. Steatoda grossa). If the full scientific name has already been mentioned somewhere prior in your writing, it is fine to abbreviate the genus, but not the species (e.g. S. grossa is fine, but Steatoda g. is not).
Seta: (pl: setae) hair; it can be feathery, clubbed, plumose, stiff, simple, urticating, etc. Most of the setae on a spider’s body perform sensory tasks, such as hearing and feeling. Even the smallest of hairs have nerves inside them that send information to the spider’s brain. Most tarantulas fling their urticating hairs as a defense mechanism. Some leg hairs, called trichobothria, react to low-frequency vibrations and air currents. The abdominal hairs of the European Water Spider (Argyroneta aquatica) are necessary for establishing the air bubble that surrounds it during diving. Wolf Spiders have “knobbed” hairs on their abdomen that help the spiderlings hang on to their mother. Some hairs are used for grooming, while still others are used for brushing silk from the spinnerets. The Cobweb, also called Comb-footed, spiders have bristles on their back legs that help pull the silk out and around their prey.
Sexual dimorphism: the condition in which males of a species differ from females of the same species in details of size, structure, shape, and color.
Silk: a liquid protein that is secreted from the spinning glands and then pushed through the tiny spigots of the spinnerets. The pulling and stretching of the liquid silk causes the proteins to line up parallel to one another, thus transitioning the liquid silk into a solid thread. This process is irreversible and has nothing to do with exposure to air. The solid threads pulled from the spinnerets are then used to make webs, egg sacs, draglines, and snares. Spider silk’s tensile strength is half that of steel, and surpasses tendon, rubber, bone, and cellulose.
Species: the taxonomic rank after genus that includes closely related organisms that are potentially able to breed with one another. If the genus of a creature is known, but the species isn’t, you will see something to this effect: Steatoda sp., where “sp.” is simply an abbreviation of the word “species”. In the plural (more than one) form, this abbreviation would be “spp.” (e.g. one Steatoda sp., six Steatoda spp.)
Spider: a predatory invertebrate animal with eight legs and two body segments. It is popularly thought to be an insect of the Class Insecta, but it is actually an arachnid of the Class Arachnida.
Spiderling: a baby spider, usually newly emerged from the egg sac.
Spinnerets: finger-like silk spinning organs located at the posterior end of the abdomen. At the tip of every finger-like extension, there are hundreds of tiny spigots that extrude the silk. Spiders originally had four pairs of spinnerets but through the eons, evolution has altered that. Today, we see two or three pairs and some groups of spiders have a cribellum and/or colulus, which are remnant, or vestigial, organs. While the colulus seems to have no function whatsoever, the cribellum, in fact, does play an important role in web building.
Stabilimentum: (pl: stabilimenta) a conspicuous structure, or web decoration, that certain web-making spider species include in their web. It was originally suggested in 1893, by French arachnologist Eugène Simon, that the structure served to add stability to the web, hence the name stabilimentum. Recent studies have mostly proven otherwise, however, and new theories are still under debate. The most widely accepted ones include 1) warnings to larger animals, such as birds, who may accidentally destroy the web 2) prey attraction and 3) camouflage. Examples of stabilimentum building species include those of the Argiopegenus, who are occasionally called “writing spiders” due to the zig-zag patterns they create on the web using only silk. Also, spiders of the Cyclosa genus create stabilimenta using their dead prey and egg sacs by aligning them in a row across the hub of the web. This technique has evolved independently many times over, therefore different species use different building materials for their stabilimenta.
Sternum: the hard plate covering the bottom side of the cephalothorax; breastplate; the chest armor.
Sub-adult: (see “immature”)
Synanthrope: an organism associated with humans and their habitat; i.e. cellar spiders are synanthropic spiders.
Tarsus: (pl: tarsi) the 7th and final segment of the leg and pedipalp; the “foot”. See also the entry for Legs & Leg Segments.
Taxon: (pl: taxa) any group or rank in a biological classification into which related organisms are classified (e.g. kingdom, phylum, class, order, family, genus, species).
Taxonomic key: a device used by scientists for identifying unknown organisms. These keys are constructed so that the user is presented with a series of choices about the characteristics of the unknown organisms; by making the correct choice at each step of the key, the user is ultimately led to the identity of a specimen.
Taxonomy: the science of finding, describing, classifying, and naming organisms, including the studying of the relationships between taxa and the principles underlying such a classification.
Tibia: (pl: tibiae) the 5th segment of the leg or pedipalp; located between the patella and the metatarsus of the leg; in the pedipalp, between the patella and the tarsus (pedipalps lack a metatarsus). See also the entry for Legs & Leg Segments.
Trichobothrium: (pl: trichobothria) long, slender, sensory hairs that grow perpendicularly from the leg. These specialized hairs are used to sense vibrations and wind currents, including even the slightest movement from the flutter of insect wings!
Trochanter: (pl: trochanters) a small, short segment of the leg or pedipalp between the coxa and the femur. See also the entry for Legs & Leg Segments.
Tubular tracheae: respiratory tubes that open at a spiracle located on the underside of the abdomen. They permeate the body of the spider and transport oxygen to and from the tissues. They are the more advanced form of respiration when compared to book lungs but some spiders use both. Also, see “book lungs” entry.
Urticating hairs: barb covered abdominal hairs found on most tarantulas. When threatened, the tarantula uses its back legs to brush the urticating hairs off into the air, creating a protective cloud. Each hair is covered with hundreds of tiny hooks and barbs that cause severe itching when in contact with skin, especially in the nose and eye region. Experiments show that these hairs can work themselves 2mm deep into human skin. Museum curators can testify that this happens quite inadvertently even when working with dead tarantulas, both preserved in alcohol and dry exuviae.
Ventral: having to do with the underside; i.e. a ventral view.
Venom: a substance primarily designed to paralyze a spider’s prey. Any other use, such as a defensive envenomation on a human, is secondary. All spiders possess venom glands, with the exception of these three small families: Uloboridae, Holarchaeidae, and Liphistiidae. Chemically, spider venom may contain many different substances, but is mostly comprised of neurotoxic polypeptides, biogenic amines, and amino acids. Some spiders possess strong and quick-acting venom, while others have much less effective toxins. It is important to note that out of over 42,500 known species of spider on Earth, only about 20-30 of them possess venom that can be dangerous to humans.