Spiders have only two body regions and eight legs. This classifies them as arachnids where as those which have three body regions and six legs are classified as insects. Spiders are predatory invertebrate animals that have two body segments, eight legs, no chewing mouth parts and no wings. All spiders produce silk, a thin, strong protein strand extruded by the spider from spinnerets most commonly found on the end of the abdomen. Many species use it to trap insects in webs, although there are also many species that hunt freely. Silk can be used to aid in climbing, form smooth walls for burrows, build egg sacs, wrap prey, and temporarily hold sperm, among other applications. Most spiders inject venom to protect themselves or to kill prey. However, in southeast Georgia, only the black widow and the brown recluse are considered dangerous.
Spiders, unlike insects, have only two body segments (tagmata) instead of three: a fused head and thorax (called a cephalothorax or prosoma) and an abdomen (called the opisthosoma).The abdomen and cephalothorax are connected with a thin waist called the pedicle or the pregenital somite, a trait that allows the spider to move the abdomen in all directions. They have pedipalps (or just palps), at the base of which are coxae or maxillae next to their mouth that aid in ingesting food; the ends of the palp are modified in adult males into elaborate and often species-specific structures used for mating. Since they have no antennae, they use specialised and sensitive hairs on their legs to pick up scent, sounds, vibrations and air currents. Spiders usually have eight eyes in various arrangements, although some have four or even two eyes. Several families of hunting spiders, such as jumping spiders and wolf spiders, have fair to excellent vision. The main pair of eyes in jumping spiders even see in color. However, most spiders that lurk on flowers, webs, and other fixed locations waiting for prey tend to have very poor eyesight; instead they possess an extreme sensitivity to vibrations, which aids in prey capture. Vibration sensitive spiders can sense vibrations from such various mediums as the water surface, the soil or their silk threads. Also changes in the air pressure can be detected in the search for prey. The abdomen has no appendages except from one to four (usually three) modified pairs of movable telescoping organs called spinnerets, which produce silk.
Spiders can only eat their food in liquid form. For this purpose predigestion is carried out both internally and externally to liquefy the tissues of their prey. Some spiders do this by spitting up digestive juices onto prey while chewing it with their chelicerae. The resulting liquefied "soup" is then then sucked up by the spider. Dense combs of hairs around the mouth filter out solids while the spider ingests the liquids. Undigested or uneaten parts of the prey are later discarded. Some spiders do not chew their food, but inject digestive fluids from their stomachs directly into the body of the prey to liquefy the inner tissues and organs. The spider then sucks out the liquefied tissues, eventually leaving the empty outer exoskeleton of the prey. Many spiders will store prey temporarily. Web-building spiders that have made a shroud of silk to quiet their envenomed prey's death struggles will often leave them in these shrouds and then consume them later.
The time between when an egg is fertilized and when the spider begins to take the shape of an adult spider is referred to as the embryonic stage. As the spider enters the larval stage, it begins to look more and more like a full grown spider. It enters the larval stage as a prelarva and, through subsequent molts, reaches its larval form, a spider-shaped animal feeding off its yolk supply. After a few more molts (also called instars) body structures become differentiated. Soon, all organ systems are complete and the animal begins to hunt on its own; it has reached the nympho-imaginal stage.This stage is differentiated into two sub-stages: the nymph, or juvenile stage and the adult stage. A spider does not become sexually mature until it makes the transition from nymph to adult. Once a spider has reached the adult stage, it will remain there until its death.
Spiders reproduce by means of eggs, which are packed into silk bundles called egg sacs. Spiders often use elaborate mating rituals (especially the visually advanced jumping spiders) to allow conspecifics to identify each other and to allow the male to approach and inseminate the female without triggering a predatory response. If the approach signals are exchanged correctly, the male spider must (in most cases) make a timely departure after mating to escape before the female's normal predatory instincts return. Sperm transmission from male to female occurs indirectly. When a male is ready to mate, he spins a web pad upon which he discharges his seminal fluid. He then dips his pedipalps (also known as palpi), the small, leg-like appendages on the front of his cephalothorax, into the seminal fluid, picking it up by capillary attraction. Mature male spiders have swollen bulbs on the end of their palps for this purpose, and this is a useful way to identify the sex of a spider in the field. With his palps thus charged he goes off in search of a female. Copulation occurs when the male inserts one or both palps into the female's genital opening, known as the epigyne. He transfers his seminal fluid into the female by expanding the sinuses in his palp.