# Spider By [Vortex](https://paragraph.com/@vortex) · 2022-06-08 --- **Spiders** ([order](https://en.wikipedia.org/wiki/Order_\(biology\)) **Araneae**) are air-breathing [arthropods](https://en.wikipedia.org/wiki/Arthropod) that have eight legs, [chelicerae](https://en.wikipedia.org/wiki/Chelicerae) with fangs generally able to inject [venom](https://en.wikipedia.org/wiki/Venom),[\[2\]](https://en.wikipedia.org/wiki/Spider#cite_note-2) and [spinnerets](https://en.wikipedia.org/wiki/Spinnerets) that extrude [silk](https://en.wikipedia.org/wiki/Spider_silk).[\[3\]](https://en.wikipedia.org/wiki/Spider#cite_note-SeldenAndShear2009-3) They are the largest order of [arachnids](https://en.wikipedia.org/wiki/Arachnid) and rank seventh in total species diversity among all [orders](https://en.wikipedia.org/wiki/Order_\(biology\)) of organisms.[\[4\]](https://en.wikipedia.org/wiki/Spider#cite_note-sebastin-4)[\[5\]](https://en.wikipedia.org/wiki/Spider#cite_note-Dimitrov-5) Spiders are found worldwide on every continent except for [Antarctica](https://en.wikipedia.org/wiki/Antarctica), and have become established in nearly every land [habitat](https://en.wikipedia.org/wiki/Habitat). As of August 2021, 49,623 spider [species](https://en.wikipedia.org/wiki/Species) in 129 [families](https://en.wikipedia.org/wiki/Family_\(biology\)) have been recorded by [taxonomists](https://en.wikipedia.org/wiki/Taxonomy_\(biology\)).[\[1\]](https://en.wikipedia.org/wiki/Spider#cite_note-WSC_stats-1) However, there has been dissension within the [scientific community](https://en.wikipedia.org/wiki/Scientific_community) as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.[\[6\]](https://en.wikipedia.org/wiki/Spider#cite_note-Bioofspiders-6) Anatomically, spiders (as with all arachnids) differ from other arthropods in that the usual body [segments](https://en.wikipedia.org/wiki/Segmentation_\(biology\)) are fused into two [tagmata](https://en.wikipedia.org/wiki/Tagma_\(biology\)), the [cephalothorax](https://en.wikipedia.org/wiki/Cephalothorax) or prosoma, and the [opisthosoma](https://en.wikipedia.org/wiki/Opisthosoma), or abdomen, and joined by a small, cylindrical [pedicel](https://en.wikipedia.org/wiki/Glossary_of_spider_terms#pedicel), however, as there is currently neither paleontological nor embryological evidence that spiders ever had a separate thorax-like division, there exists an argument against the validity of the term cephalothorax, which means fused [cephalon](https://en.wikipedia.org/wiki/Cephalon_\(arthropod_anatomy\)) (head) and the [thorax](https://en.wikipedia.org/wiki/Thorax). Similarly, arguments can be formed against use of the term abdomen, as the opisthosoma of all spiders contains a heart and respiratory organs, organs atypical of an abdomen.[\[7\]](https://en.wikipedia.org/wiki/Spider#cite_note-7) Unlike [insects](https://en.wikipedia.org/wiki/Insect), spiders do not have [antennae](https://en.wikipedia.org/wiki/Antenna_\(biology\)). In all except the most primitive group, the [Mesothelae](https://en.wikipedia.org/wiki/Mesothelae), spiders have the most centralized nervous systems of all arthropods, as all their [ganglia](https://en.wikipedia.org/wiki/Ganglion) are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no [extensor](https://en.wikipedia.org/wiki/Extensor) muscles in their limbs and instead extend them by hydraulic pressure. Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of glands. [Spider webs](https://en.wikipedia.org/wiki/Spider_web) vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than [orb-weaver spiders](https://en.wikipedia.org/wiki/Orb-weaver_spider). Spider-like [arachnids](https://en.wikipedia.org/wiki/Arachnid) with silk-producing [spigots](https://en.wikipedia.org/wiki/Spigot) appeared in the [Devonian](https://en.wikipedia.org/wiki/Devonian) [period](https://en.wikipedia.org/wiki/Period_\(geology\)) about [386](http://tools.wmflabs.org/timescale/?Ma=386) million years ago, but these animals apparently lacked spinnerets. True spiders have been found in [Carboniferous](https://en.wikipedia.org/wiki/Carboniferous) rocks from [318 to 299](http://tools.wmflabs.org/timescale/?Ma=318%E2%80%93299) million years ago, and are very similar to the most primitive surviving [suborder](https://en.wikipedia.org/wiki/Order_\(biology\)), the [Mesothelae](https://en.wikipedia.org/wiki/Mesothelae). The main groups of modern spiders, [Mygalomorphae](https://en.wikipedia.org/wiki/Mygalomorphae) and [Araneomorphae](https://en.wikipedia.org/wiki/Araneomorphae), first appeared in the Triassic period, before [200](http://tools.wmflabs.org/timescale/?Ma=200) million years ago. The species [_Bagheera kiplingi_](https://en.wikipedia.org/wiki/Bagheera_kiplingi) was described as [herbivorous](https://en.wikipedia.org/wiki/Herbivory) in 2008,[\[8\]](https://en.wikipedia.org/wiki/Spider#cite_note-CBio2009-8) but all other known species are [predators](https://en.wikipedia.org/wiki/Predator), mostly preying on insects and on other spiders, although a few large species also take birds and lizards. It is estimated that the world's 25 million tons of spiders kill 400–800 million tons of prey per year.[\[9\]](https://en.wikipedia.org/wiki/Spider#cite_note-9) Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, [lassoing](https://en.wikipedia.org/wiki/Lasso) it with sticky [bolas](https://en.wikipedia.org/wiki/Bolas), mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the [genus](https://en.wikipedia.org/wiki/Genus) [_Portia_](https://en.wikipedia.org/wiki/Portia_\(spider\)) show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, so they liquefy their food by flooding it with digestive [enzymes](https://en.wikipedia.org/wiki/Enzyme). They also grind food with the bases of their [pedipalps](https://en.wikipedia.org/wiki/Pedipalp), as arachnids do not have the mandibles that crustaceans and insects have. To avoid being eaten by the females, which are typically much larger, male spiders identify themselves to potential mates by a variety of complex [courtship](https://en.wikipedia.org/wiki/Courtship) rituals. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the [widow spiders](https://en.wikipedia.org/wiki/Latrodectus), to co-operative hunting and food-sharing. Although most spiders live for at most two years, [tarantulas](https://en.wikipedia.org/wiki/Tarantula) and other [mygalomorph](https://en.wikipedia.org/wiki/Mygalomorphae) spiders can live up to 25 years in captivity. While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting [pesticides](https://en.wikipedia.org/wiki/Pesticide). Spider silk provides a combination of lightness, strength and [elasticity](https://en.wikipedia.org/wiki/Elasticity_\(physics\)) that is superior to that of synthetic materials, and spider silk genes have been inserted into [mammals](https://en.wikipedia.org/wiki/Mammal) and [plants](https://en.wikipedia.org/wiki/Plant) to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and [mythology](https://en.wikipedia.org/wiki/Mythology) symbolizing various combinations of patience, cruelty and creative powers. An irrational fear of spiders is called [arachnophobia](https://en.wikipedia.org/wiki/Arachnophobia). source: [en.wikipedia.org/wiki/Spider](http://en.wikipedia.org/wiki/Spider) --- *Originally published on [Vortex](https://paragraph.com/@vortex/spider)*