The cribellate spiders were the first spiders to build specialized prey-catching webs.
Spiders that do not have powerful chelicerae (fanglike structures near the mouth, which aid in grasping or piercing objects) secrete digestive fluids into their prey from a series of ducts perforating their chelicerae.
Spiders of this remnant suborder are very rare and are among the most "primitive" types of spiders in existence.
People with arachnophobia tend to feel uneasy in any area they believe could harbor spiders or that has visible signs of their presence, such as webs.
Very unusual behavior is seen in spiders of the genus Tidarren: the male amputates one of his palps before maturation and enters his adult life with one palp only.
The Araneomorphae, (previously called the Labidognatha), are often known as the modern spiders.
Spiders have a great range of variation and lifestyle, although all are predatory.
Other species of spiders do not use webs for capturing prey, instead pouncing from concealment (e.g.
The main pair of eyes in jumping spiders even sees in colors.
The study of spiders is known as arachnology.
The largest and heaviest spiders occur among the tarantulas, which can have body lengths as great as nine centimeters.
Some tarantulas have a second kind of defense, a patch of urticating (stinging, or whipping) hair, or urticating setae, on their abdomens, which is generally absent on modern spiders and Mesothelae.
Many spiders may only live for about a year, but a number will live two years or more, overwintering in sheltered areas.
All spiders produce silk, a thin, strong protein strand extruded by the spider from spinnerets most commonly found on the end of the abdomen.
A few species of spiders that build webs live together in large colonies and show social behavior, albeit not as well evolved as in social insects.
The annual influx of 'outdoor' spiders into houses in the fall is due to this search for a warm place to spend the winter.
Only three classes of pigment (ommochromes, bilins, and guanine) have been identified in spiders, although other pigments have been detected but not yet characterized.
All spiders have eight legs, although a few ant-mimicking species use their front legs to imitate antennae, which spiders lack.
Except for a few species of very primitive spiders (family Liphistiidae), the abdomen is not externally segmented.
The two other suborders, the Mygalomorphae (trapdoor spiders, funnel-web spiders, tarantulas) and the Araneomorphae ("modern" spiders), are sometimes grouped together as Opisthothelae.
Spiders usually have eight eyes in various arrangements, a fact which is used to aid in taxonomically classifying different species.
Spiders occur in a large range of sizes.
Despite their generally broad prey ranges, spiders are one of the most important links in the regulation of the populations of insects.
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.
Arachnophobia is a specific phobia, an abnormal fear of spiders.
Spiders have an open circulatory system; i.e., they do not have true blood, or veins to convey it.
All spiders except those in the families Uloboridae and Holarchaeidae and in the suborder Mesothelae (together about 350 species) can inject venom to protect themselves or to kill and liquefy prey.
Web-weaving spiders that have made a shroud of silk to quiet their envenomed prey's death struggles will generally leave them in these shrouds and then consume them at their leisure.
The exception to this rule are the assassin spiders, whose cephalothorax seems to be almost divided into two independent units.
Other spiders with more powerfully built chelicerae masticate the entire body of their prey and leave behind only a relatively small residue of indigestible materials.
Most of the spiders that people encounter in daily life belong to this suborder, which makes up 94 percent of all spider species.
True spiders (thin-waisted arachnids) evolved about 400 million years ago, and were among the first species to live on land.
The spitting spiders have modified their poison glands to produce a mixture of venom and sticky substance that works as glue and immobilizes the prey.
Spiders in several families (eg., Araneidae, Tetragnathidae, Nephilidae) spin the familiar spiral snare that most people think of as the typical spider web.
Bolas spiders in the family Araneidae use sex pheromone analogs to capture only the males of certain moth species.
Some very small spiders in moist and sheltered habitats have no breathing organs at all, and instead breathe directly through their body surface.
A few spiders are more specialized in their prey capture.
Spiders, even small ones, may however bite humans when pinched.
Most spiders are unlikely to bite humans because they do not identify humans as prey.
Spiders show a wide range of behavior, from the ballet-like mating dances of certain jumping spiders to the seeming athletics of bolas spiders snatching their prey.
The fear of spiders can be treated by any of general techniques suggested for specific phobias.
Vibration sensitive spiders can sense vibrations from such various mediums as the water surface, the soil or their silk threads.
Some spiders spin funnel-shaped webs, others make sheet webs; spiders like the black widow make tangled, maze-like, webs, and still others make the spiral "orb" webs that are most commonly associated with spiders.
None of these spiders will intentionally "come after you," but they should be removed from one's house to avoid accidental injury.
By the Jurassic period, the sophisticated aerial webs of the orb-weaving spiders had already developed to take advantage of the rapidly diversifying groups of insects.
The ability to weave orb webs is thought to have been "lost," and sometimes even re-evolved or evolved separately, in different breeds of spiders since its first appearance.
Some spiders manage to use the 'signaling snare' technique of a web without spinning a web at all.
Their eyes are single lenses rather than compound eyes, ranging from simple light/dark-receptors to eyes rivaling those of a pigeon (some jumping spiders).
The Liphistiidae are burrowing spiders only found in Southeast Asia, China, and Japan with about ninety species in five genera.
Several types of water-dwelling spiders will rest their feet on the water's surface in much the same manner as an orb-web user.
Mygalomorph and Mesothelae spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen.
Many genera, such as the widow spiders, inject neurotoxins that can spread through the prey's entire body and interfere with vital body functions.
Spiders of the genus Dysdera capture and eat sowbugs, pillbugs, and beetles, while pirate spiders eat only other spiders.
Spiders are predatory, invertebrate animals with two body segments, eight legs, no chewing mouth parts, and no wings.
Spiders reproduce by means of eggs, which are packed into silk bundles called egg sacs.
The common northern hemisphere 'funnel-web', 'house' or 'grass' spiders are only superficially similar to the notorious Sydney funnel-web spider, and are generally considered to be quite harmless.
All spiders will attempt to protect themselves by biting, especially if they are unable to flee.
Among smaller araneomorph spiders, we can find species who have evolved also the anterior pair of book lungs into trachea, or the remaining book lungs are simply reduced or missing.
Spiders lack the ability to chew their food.
Spiders, especially larger sorts, are eaten routinely or as a delicacy in various parts of the world, including Cambodia, Thailand, the Solomon Islands, and parts of South America.
Several plesiomorphic characters may be useful in recognizing these spiders: there are tergite plates on the dorsal side and the almost-median position of the spinnerets on the ventral side of the opisthosoma.
Spiders bite their prey, and occasionally animals that cause them pain or threaten them, for two purposes.
Many spiders do not build webs for catching prey, but rather hunt on ground or in plants.
Spiders, unlike insects, have only two body segments (a trait called tagmata) instead of three: a fused head and thorax (called a cephalothorax or prosoma) and an abdomen (called the opisthosoma).
An abnormal fear of spiders (arachnophobia) is one of the most common phobias and spiders are often looked at as something to be eliminated.
trapdoor spiders) or running them down in open chase (e.g.
Spiders have developed several different respiratory anatomies, based either on book lungs, a tracheal system, or both.