Spiders!
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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 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.
All but about 150 species of spiders (in the families Uloboridae and Holarchaeidae, and the suborder Mesothelae) can inject venom to protect themselves or to kill and liquefy prey. Only up to 200 species, however, have bites that can pose health problems to humans. Many larger species' bites may be painful, but will not produce lasting health concerns.
Spider Morphology
Spider anatomy
(1) four pairs of legs(2) cephalothorax
(3) opisthosomaSpiders, 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 exception to this rule are the assassin spiders, whose cephalothorax seems to be almost divided into two independent units. Except for a few species of very primitive spiders (family Liphistiidae), the abdomen is not externally segmented. 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. This waist is actually the last segment (somite) of the cephalothorax and is lost in most other members of the Arachnida (in scorpions it is only detectable in the embryos).
Spider Cephalothorax
All spiders have eight legs, althoug a few ant-mimicking species use their front legs to imitate antennae, which spiders lack. Their eyes are single lenses rather than compound eyes, ranging from simple light/dark-receptors to eyes rivalling that of a pigeon (some jumping spiders).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 don't have any antennae, they are using specialised and sensitive hairs on their legs to pick up scent, sounds, vibrations and air currents.
Because they can't chew their food, they have, like other arachnids, a tiny mouth they use as a short drinking straw to suck up the liquid parts of their prey. However they are able to eat their own silk.
Spider Sense organs
Multiple eyes of the jumping spider Platycryptus undatus.Spiders usually have eight eyes in various arrangements, a fact which is used to aid in taxonomically classifying different species. Most species of the Haplogynae have six eyes, although some have eight (Plectreuridae), four (eg., Tetrablemma) or even two (most Caponiidae) eyes. Sometimes one pair of eyes is better developed than the rest, or even, in some cave species, there are no eyes at all. 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 sees in colors. Net-casting spiders have enormous, compound lenses that give a wide field of view and gather available light very efficiently.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.
Spider Respiration and circulation
Spiders have an open circulatory system; i.e., they do not have true blood, or veins to convey it. Rather, their bodies are filled with haemolymph, which is pumped through arteries by a heart into spaces called sinuses surrounding their internal organs.Spiders have developed several different respiratory anatomies, based either on book lungs, a tracheal system, or both. 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. This is also the case for some basal araneomorph spiders like the family Hypochilidae, but the remaining members of this group have just the anterior pair of book lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs. This system has most likely evolved in small ancestors to help resist desiccation. The trachea were originally connected to the surroundings through a pair of spiracles, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and migrated posterior close to the spinnerets.
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, and in a very few the book lungs have developed deep channels, apparently signs of evolution into tracheae. Some very small spiders in moist and sheltered habitats don't have any breathing organs at all, as they are breathing directly through their body surface. In the tracheal system oxygen interchange is much more efficient, enabling cursorial hunting (hunting involving extended pursuit) and other advanced characteristics as having a smaller heart and the ability to live in dryer habitats.
Spider Digestion
Digestion is carried out internally and externally. Spiders that do not have powerful chelicerae secrete digestive fluids into their prey from a series of ducts perforating their chelicerae. These digestive fluids dissolve the prey's internal tissues. Then the spider feeds by sucking the partially digested fluids out. Other spiders with more powerfully built chelicerae masticate the entire body of their prey and leave behind only a relatively small glob of indigestible materials. Spiders consume only liquid foods. Many spiders will store prey temporarily. 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.Spider Spinnerets
The abdomen has no appendages except from one to four (usually three) modified pairs of movable telescoping organs called spinnerets, which produce silk. The suborder Mesothelae is unique in having only two types of silk glands - thought to be the ancestral condition. All other spiders have the spinnerets further towards the posterior end of the body where they form a small cluster, and the anterior central spinnerets on the tenth segment are lost or reduced (suborder Mygalomorphae), or modified into a specialised and flattened plate called the cribellum (parts of suborder Araneomorphae), which produces a thread made up of hundreds to thousands of very fine dry silk fibers resulting in a woolly structure that traps prey. The cribellate spiders were the first spiders to build specialised prey catching webs. Later some groups evolved (called ecribellate) that use silk threads dotted with sticky droplets to capture prey ranging from small arthropods to sometimes even small bats and birds.Spider Life cycle
Pisaura mirabilis guarding her egg sacBird Dropping Spider with its unusual eggs
Spiderlings on a web
The exoskeleton of a spider after moultingThe spider life cycle progresses through three stages: the embryonic, the larval, and the nympho-imaginal.
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 an adult spider. It enters the larval stage as a prelarva and, through subsequent moults, reaches its larval form, a spider-shaped animal feeding off its yolk supply. After a few more moults (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 imago, or adult stage. A spider does not become sexually mature until it makes the transition from nymph to imago. Once a spider has reached the imago stage, it will remain there until its death. After sexual maturity is reached, the general rule is that they stop moulting, but the females of some non-araneomorph species will continue to moult the rest of their lives.
Many spiders may only live for about a year, but a number will live two years or more, overwintering in sheltered areas. The annual influx of 'outdoor' spiders into houses in the fall is due to this search for a warm place to spend the winter. It is common for tarantulas to live around twenty years.
Spider Reproduction
Spiders reproduce by means of eggs, which are packed into silk bundles called egg sacs. Spiders often use elaborate mating rituals (especially in 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. Once the sperm is inside her, she stores it in a chamber and only uses it during the egg-laying process, when the eggs comes into contact with the male sperm for the first time and are fertilized; this may be why the vivipary has never evolved in spiders.
Very unusual behaviour 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 palpi constitute 20% of the body mass of males of this species, and since this weight greatly impedes its movement, by detaching one of the two he gains increased mobility. In the Yemeni species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime the female feeds on the palpless male.
Spider Sacrificial males
Even in some species of black widow, which are named exactly for this belief, the male may live in the female's web for some time without being harmed. However, the male of the closely related Australian redback spider is killed ritually by the females after it inserts its second palpus in the female genital opening; in over 60% of cases the female then eats the male. Males that 'sacrifice' themselves gain the benefit of increasing their paternity relative to males who do not get cannibalized, by feeding the egg-laying female.In many other species, males are sometimes killed by females. In at least some of these cases it's likely that the males are simply mistaken as prey.
Spider Ecology
Spiders have a great range of variation and lifestyle, although all are predatory.While spiders are generalist predators, in actuality their different methods of prey capture often determine the type of prey taken. Thus web-building spiders rarely capture caterpillars, and crab spiders that ambush prey in flowers capture more bees, butterflies and some flies than other insects. Groups of families that tend to take certain types of prey because of their prey capture methods are often called guilds. A few spiders are more specialized in their prey capture. Dysdera captures and eats sowbugs, pillbugs and beetles, while pirate spiders eat only other spiders. Bolas spiders in the family Araneidae use sex pheromone analogs to capture only the males of certain moth species. Despite their generally broad prey ranges, spiders are one of the most important links in the regulation of the populations of insects. Every day on a meadow they devour over 10 g/m' of insects and other arthropods.
Spider Behavior
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. Most diversity comes with the mode of predation, for example whether the spider waits for it in its orb web, or hunts it down.Spider Predatory techniques
A spider hiding in its leaf (located at the centre of its web)There are many families of spiders, and the ways that they catch prey are diverse. But whether they catch insects, fish, small mammals, small birds, or some other small form of life, as soon as a spider makes contact with its prey it will generally attempt to bite it.Spiders bite their prey, and occasionally animals that cause them pain or threaten them, to do two things. First, they inflict mechanical damage, which, in the case of a spider that is as large as or larger than its prey, can be severe. Second, they can choose to inject venom through their hollow fangs. Many genera, such as the widow spiders, inject neurotoxins that can spread through the prey's entire body and interfere with vital body functions. Other genera inject venom that operates to produce tissue damage at the site of the bite. Genera such as that of the brown recluse spider produce a necrotoxin. The necrotoxin is injected into prey where it causes the degradation of cell membranes. In the larger victims that do not die from these attacks, painful lesions over a fairly wide area of the body can remain active for fairly long periods of time. The spitting spiders have modified their Poison glands to produce a mixture of venom and sticky substance that works as glue and immobilises the prey.
Although there are no vegetarian spiders, some species in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae have been observed feeding on plant nectar. Several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages in captivity.
Spider Spider webs
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. These webs may be made with sticky capture silk, or with "fluffy" capture silk, depending on the type of spider. Webs may be in a vertical plane (most orb webs), a horizontal plane (sheet webs), or at any angle in between. Most commonly found in the sheet-web spider families, some webs will have loose, irregular tangles of silk above them. These tangled obstacle courses serve to disorient and knock down flying insects, making them more vulnerable to being trapped on the web below. They may also help to protect the spider from aerial predators such as birds and wasps.Having completed its web, a spider in the forests of Malaysia awaits its prey. Appears to be some species of Nephila.The spider, after spinning its web, will then wait on, or near, the web for a prey animal to become trapped. The spider can sense the impact and struggle of a prey animal by vibrations transmitted along the web lines.
Other species of spiders do not use webs for capturing prey directly, instead pouncing from concealment (e.g. trapdoor spiders) or running them down in open chase (e.g. wolf spiders). The net-casting spider balances the two methods of running and web-spinning in its feeding habits. This spider weaves a small net which it attaches to its front legs. It then lurks in wait for potential prey and, when such prey arrives, lunges forward to wrap its victim in the net, bite and paralyze it. Hence, this spider expends less energy catching prey than a primitive hunter such as the Wolf spider. It also avoids the energy cost of weaving a large orb-web. The diving bell spider does not use its web directly in prey capture, but has modified it into an underwater diving bell. Even species whose ancestors were building spiral orb webs have given rise to spiders who no longer make webs, for instance some Hawaiian spiny-legged spiders (genus Tetragnatha, family Tetragnathidae) which have abandoned web construction entirely.
Some spiders manage to use the 'signalling snare' technique of a web without spinning a web at all. 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. When an insect falls onto the water and is ensnared by surface tension, the spider can detect the vibrations and run out to capture the prey.
A golden silk orb-weaver (Nephila clavipes?), member of the family Tetragnathidae Hunting spiders
An ant-mimicking jumping spiderMany spiders do not build webs for catching prey. Some examples include:
Brazilian wandering spider Brown recluse spider Huntsman spiders Jumping spiders Lynx spiders Nursery web spiders Spitting spiders Tarantulas Wolf spiders (Lycosidae) Yellow sac spider Assassin spider
Spiders as Ambush predators
Some actively lure prey (the Bolas spiders) and may capture them with a sticky ball of silk on a line; others (like the crab spiders, trapdoor spiders, or the six-eyed sand spider) wait in a high-traffic area and directly attack their prey from ambush.Spider Defense
All spiders will attempt to protect themselves by biting, especially if they are unable to flee. Some tarantulas have a second kind of defense, a patch of urticating hairs, or urticating setae, on their abdomens, which is generally absent on modern spiders and Mesothelae. These ultra-fine hairs causes irritation and sometimes even allergic reactions in the attacker. Certain other species have specialized defense tactics. For example, the Golden Wheeling spider (Carparachne aureoflava) of the desert of Namibia escapes tarantula hawks (a species of wasp that lays its eggs in a paralyzed spider so the larvae have enough food when they hatch) by flipping onto its side and cartwheeling away.Social spiders
A few species of spiders that build webs are living together in large colonies and are showing social behavior, even if it is not as well evolved as in social insects. The most social species are probably Anelosimus eximius, which can form colonies that counts up to fifty thousand individuals.Spider Web types
Tangleweb spiders
Black widowMembers of this group (family Theridiidae) are characterized by irregular, messy-looking, tangled, three-dimensional (non-sticky) webs, generally low and anchored to the ground or floor and wall. They are commonly found in or near buildings; some build webs in bushes. The spider generally hangs in the center of its web, upside-down. Prey is generally ground-dwelling insects such as ants or crickets, in addition to small flying insects. These include the infamous black widows, the minute Happyface spider, and thousands of other species.Orb web spiders
Spiders in several families (eg., Araneidae, Tetragnathidae, Nephilidae) spin the familiar spiral snare that most people think of as the typical spider web. On average, an orb-weaving spider takes 30 minutes to an hour to weave a web. They range in size from quite large (6+ cm) to very small.Brazilian wandering spider
Scientific classificationKingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Araneae
Genus: Phoneutria
Perty, 1833
Diversity
5 species
Type species
Phoneutria fera
Perty, 1833
Species
P. bahiensis
P. boliviensis
P. fera
P. nigriventer
P. reidyi
The Brazilian wandering spider (Phoneutria spp.) or Armadeira (as it is known in Portuguese) is an aggressive and highly venomous spider named as such because it was first discovered in Pantanal, though this genus is known to exist elsewhere in South and Central America. This spider is a member of the Ctenidae family of wandering spiders.
The Brazilian wandering spider appeared in the Guinness Book of World Records 2007 for the most venomous animal.
Brazilian wandering spider Phoneutria
Phoneutria spp.(Greek for "Murderess") is actually a genus with five known similar species whose members are highly venomous. They include some of the relatively few species of spiders that present a threat to human beings. The Brazilian wandering spider can grow to have a leg span of up to 4-5 inches (10-13 cm).These spiders are notorious both due to their toxic venom, and because they are not reluctant to attack people who appear threatening. Of the five species known, P. nigriventer and P. fera most frequently receive mention in mass-media publications. P.nigriventer species are responsible for most cases of venom intoxication in Brazil because this species is commonly found in highly populated areas of Brazil, namely the South-eastern states: São Paulo, Minas Gerais, Rio de Janeiro and Espírito Santo. The P. fera is native to the northern portion of South America, especially the Brazilian Amazônia, Venezuela and French Guiana.
Recent studies suggest that these spiders only inject venom in approximately one-third of their bites and may only inject a small amount in another third. However, research in this area is hindered by the d ifficulty of identifying particular subspecies.
Bites from these spiders may result in only a couple of painful pinpricks to full-blown envenomation. In either case, people bitten by a Phoneutria or any Ctenid should seek immediate emergency treatment as the venom is possibly life threatening. The Phoneutria fera and nigriventer are the two most commonly implicated as the most virulent of the Phoneutria spiders. The Phoneutria not only has a potent neurotoxin, but is reported to have one of the most excruciatingly painful envenomations of all spiders due to its high concentration of serotonin.
The wandering spider is so-called because it wanders the jungle floor, rather than residing in a lair or maintaining a web. This attribute is another reason it is considered so dangerous. In densely populated areas, Phoneutria species usually search for cover and dark places to hide during daytime, leading it to hide within houses, clothes, cars, boots, boxes and log piles; thus generating accidents when people disturb it. Its other common name - the "banana spider" - as attributed because it is occasionally found as a 'stowaway' within shipments of bananas.
Despite its reputation as the world's deadliest spider, there are multiple studies that dispute its capacity for fatal human envenomation. One study suggested that only 2.3% of bites (mainly in children) were serious enough to require antivenom. However, other sources suggest it is the most dangerous or toxic spider in the world based upon toxicology studies. One of the most notable and thorough studies is presented in the book "Venomous Animals and their Venoms Vol. III" edited by Wolfgang Bucheral and Eleanor Buckley, and cleary demonstrate Phoneutria nigriventer's extreme toxicity in a table showing that the amount necessary to kill a 20gm mouse was only .006mg (intravenously) and .0134 subcutaneously as compared to Latrodectus mactans (Black Widow) at 0.110 and 0.2 respectively. The same study reports the death of two children killed by the same spider in São Sebastião identified as a Phoneutria, and identified by Bucheral. This demonstrates the fact that identification is key in the process of accurately associating a bite with the correct, offending species. Both P. nigriventer and P. fera are extremely dangerous. Pharmalogical studies strongly suggest the danger of Phoneutria envenomation and ranks various species of the Phoneutria genus arguably as one of the world's most dangerous spiders.
Aside from causing intense pain, the venom of the spider can also cause priapism - uncomfortable erections that can last for many hours and that can lead to impotence. The venom may eventually be used in erectile dysfunction treatments.
Brazilian wandering spider Antidote
The antidote for poison was developed by Carlos Chagas Foundation in the 60s. Due to the poison being extremely fast acting on the human body it is very difficult reach a hospital in time to be saved, carrying the antidote in trips to South American tropical rainforests is therefore highly recommended.Brazilian wandering spider In fiction
The Fear, an antagonist from the video game Metal Gear Solid 3: Snake Eater, uses the venom from the Brazilian wandering spider on his crossbow bolts to fire at the player. (Additionally, it is not confirmed if it's the most potent poison in the game itself.)Synthetic Brazilian Wandering Spider venom was also used as a murder weapon in an episode of CSI: NY.
