Spiders are invertebrate animal(s) that produce silk, have eight legs and no wings. More precisely, a spider is any member of the arachnid order Araneae, an order divided into two sub-orders: the Opisthothelae (which include the infraorders Mygalomorphae (trapdoor and tarantula spiders) and Araneomorphae (the modern spiders)) and the Mesothelae, which contains the Family Liphistiidae, burrowing spiders from Asia. more...
The study of spiders is known as arachnology.
Many spiders hunt by building webs to trap insects. These webs are made of spider silk, a thin, strong protein strand extruded by the spider from spinnerets most coomonly found on the end of the abdomen. All spiders produce silk, although not all use it to spin elaborate traps. Silk can be used to aid in climbing, forming smooth walls for burrows, building egg sacs, wrapping prey, temporarily holding sperm and for many other applications.
Morphology and development
Spiders, unlike insects, have only two body segments instead of three; a fused head and thorax (called a cephalothorax or prosoma) and an abdomen (called the opisthosoma), supported by an exoskeleton composed mainly of chitin.
Spiders also have eight legs (insects have six), no antennae, and their eyes are single lenses rather than compound eyes. Additionally spiders have pedipalps (or just palps), at the base of which are coxae or maxillae next to their mouth that aid in maasticating food; the ends of the palp are modified in adult males into elaborate and often species specific structures used for mating.
Respiration and circulation
Spiders have an open circulatory system, meaning they don't have true blood or veins for it to travel in. Rather, their bodies are filled with haemolymph, which is pumped through arteries by a heart into spaces called sinuses surrounding their organs.
Spiders have developed several different respiratory anatomies, based either on book lungs, a tracheal system, or both. Primitive mygalomorph spiders generally have only a pair of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allows air to enter and diffuse oxygen. Modern araneomorph spiders often have a single book lung in addition to spiracles which deliver air into the tracheae, where oxygen is then diffused into the haemolymph. In the tracheal system oxygen interchange is much more efficient, enabling cursorial hunting (hunting involving rapid pursuit) and other advanced characteristics.
Spiders usually have eight eyes in various arrangements, a fact which is used to taxonomically classify different species. Sometimes one pair of eyes is better developed than the rest, or there are only six pairs, or no eyes at all. Several families of hunting spiders have developed good to excellent vision, such as wolf spiders and jumping spiders. However, most spiders that lurk on flowers, webs and other fixed locations waiting for prey have very poor eyesight, but possess extreme sensitivity to vibrations for hunting.
Some tarantula have a patch of urticating hairs on their abdomens for defense, which are generally absent on modern spiders and Mesothelae. Certain other species have specialized defense tactics. For example, the Golden Wheeling spider of the desert escapes Tarantula Wasps (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.
The spider life cycle progresses through three stages: the embryonic, the larval, and the nympho-imaginal (Foelix, 1996).
Between the time an egg is fertilized and the spider begins to take the shape of a spider is referred to as the embryonic stage (Foelix, 1996). As the spider begins to look more like a spider it enters the larval stage (Foelix, 1996). It enters the larval stage as a prelarva and, through subsequent molts, it reaches its larval form, a spider-looking, non self-sufficient animal feeding off its yolk supply (Foelix, 1996). After a few more molts, also called instars, body structures become differentiated; all organ systems are complete and the animal begins to hunt on its own; it has reached the nympho-imaginal stage (Foelix, 1996). This stage is differentiated by two sub-stages: the nymph, or juvenile stage and the imago, or adult stage (Foelix, 1996). A spider does not transition from the nymph to the imago until it has become sexually mature (Foelix, 1996). Once a spider has reached the imago stage, it will remain there until its death. Many spiders may live only 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 nice warm place to spend the winter).
Spiders reproduce by eggs laid in silk bundles called egg sacs.
Spiders often use elaborate mating rituals (especially in the visually advanced jumping spiders) to allow the male to approach close enough to inseminate the female without triggering a predatory response. Assuming that the approach signals are exchanged correctly, the male spider must make a timely departure after mating to escape before the female's normal predatory instincts come back into operation.
Sperm transmission is an indirect process. When a male is ready to mate, he will spin a web pad onto which the sperm is discharged. He then dips his palps (also known as 'palpi'), the small, leg-like appendages on the front of his cephalothorax, into the sperm, 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 then goes off in search of a female. The act of copulation occurs when the male inserts one or both palps into the female's genital opening, known as the epigyne. He transfers his sperm into the female by expanding the sinuses in his palp.
Very unusual behaviour is seen in spiders of the genus Tidarren, as the male amputates one of his palps before maturation and enters his adult life with one palp only. The palpi constitute 20% of its body mass, and since this weight greatly impedes its movement, the spider detaches one of the two to gain 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. (Journal of Zoology (2001), 254:449-459 Cambridge University Press DOI:10.1017/S0952836901000954 )
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Buibui ni mnyama asiye na uti wa mgongo ambaye hutengeneza hariri, ana miguu minane na hana mabawa. "Kama spider, ni aina ya spider ya aina ya ""Araneae,"" ambayo ni sehemu ya jamii ya ""Ophistothelae,"" ambayo ni pamoja na spiders ya kisasa, na ""Mesothelae,"" ambayo ni sehemu ya jamii ya ""Liphistiidae.""" zaidi... Utafiti wa buibui unaitwa arachnology. Buibui wengi huwinda kwa kujenga utando ili kuwashika wadudu. Mtandao huu ni wa hariri ya buibui, nyuzi nyembamba na zenye nguvu za protini zinazotokana na buibui kutoka kwenye nyuzi za kugeuza ambazo hupatikana kwenye sehemu ya mwisho ya tumbo. Buibui wote hutokeza hariri, ingawa si wote wanaotumia hariri kutengeneza mitego maridadi. Silki inaweza kutumika kusaidia kupanda, kuunda kuta laini kwa ajili ya burrows, kujenga mifuko ya mayai, wrapping mawindo, muda kushikilia shahawa na kwa ajili ya matumizi mengine mengi. Spiders, tofauti na wadudu, wana sehemu mbili tu za mwili badala ya tatu: kichwa na kifua (inaitwa cephalothorax au prosoma) na tumbo (inaitwa opisthosoma), iliyoungwa mkono na exoskeleton iliyoundwa hasa na chitin. Buibui pia wana miguu minane (nyani wana sita), hawana antena, na macho yao ni lensi moja badala ya macho yaliyounganishwa. Pia, buibui wana pedipalps (au palps tu), ambayo ni coxae au maxillae karibu na mdomo wao kusaidia katika maasticating chakula; mwisho wa palp ni kubadilishwa katika wanaume wazima katika miundo ya kina na mara nyingi aina maalum kutumika kwa ajili ya kuoa. Upasuaji na Mzunguko wa Damu: Buibui wana mfumo wa mzunguko wa damu ulio wazi, ikimaanisha hawana damu halisi au mishipa ili iweze kusafiri. Mwili wao umejaa hemolymph, ambayo hupumzwa kupitia mishipa ya damu na moyo kwenye nafasi zinazoitwa sinuses zinazozunguka viungo vya mwili. Buibui wamebuni mifumo kadhaa tofauti ya kupumua, ikitegemea mapafu ya kitabu, mfumo wa tracheal, au yote mawili. Kwa kawaida, buibui aina ya mygalomorph wana mapafu mawili tu yaliyojaa hemolymph, ambapo mashimo yaliyo kwenye sehemu ya chini ya tumbo huruhusu hewa kuingia na kueneza oksijeni. Nyani wa kisasa wa aina ya araneomorph mara nyingi huwa na mapafu ya kitabu kimoja pamoja na spiracles ambayo hutoa hewa ndani ya trachea, ambapo oksijeni huenea ndani ya hemolymph. Katika mfumo wa tracheal kubadilishana oksijeni ni ufanisi zaidi, kuwezesha cursorial uwindaji (uwindaji kuhusisha kufuatilia haraka) na sifa nyingine za juu. Buibui kwa kawaida huwa na macho manane katika mpangilio mbalimbali, jambo linalotumiwa kuainisha spishi tofauti-tofauti. Wakati mwingine, jicho moja huendelea vizuri kuliko jicho jingine, au kuna jicho sita tu, au jicho lolote. Familia kadhaa za buibui wa kuwinda zimeendeleza uwezo mzuri wa kuona, kama vile buibui-mbwa-mwitu na buibui-mwitu wanaoruka. Hata hivyo, buibui wengi ambao hutazama kwenye maua, mawingu na maeneo mengine ya kudumu wakisubiri mawindo wana macho duni sana, lakini wana hisia kali sana kwa mtetemeko kwa ajili ya kuwinda. Baadhi ya tarantula wana nywele kwenye tumbo lao ili kujilinda, nywele hizo hazipatikani kwa kawaida kwenye buibui na Mesothelae wa kisasa. Spishi nyingine fulani zina mbinu za pekee za kujilinda. Kwa mfano, buibui anayeitwa Golden Wheeling wa jangwani huepuka buibui anayeitwa Tarantula Wasps (spishi ya buibui anayeweka mayai yake ndani ya buibui aliyechoma ili mabuu ya buibui awe na chakula cha kutosha wanapofungua) kwa kugeuka upande na kugeuka. Mzunguko wa maisha ya buibui unaendelea kupitia hatua tatu: kiinitete, mabuu, na nymphomaginal (Foelix, 1996). Wakati kati ya yai kufanywa na kuzaana na buibui huanza kuchukua umbo la buibui ni inajulikana kama hatua ya kiinitete (Foley, 1996). Wakati buibui huanza kufanana na buibui, huingia katika hatua ya mabuu (Foelix, 1996). Katika hatua ya kwanza ya larval, mnyama huyo huanza kugeuka na kuwa spider-like, na huanza kula yai lake. Baada ya muda mfupi, mifumo ya mwili huanza kutofautishwa, mifumo yote ya viungo imekamilika na mnyama huanza kuwinda peke yake; imefikia hatua ya nymphomania. Hatua hii ni tofauti na hatua mbili ndogo: nymph, au hatua ya vijana, na imago, au hatua ya watu wazima (Foelix, 1996). Nyigu hawezi kugeuka kutoka nymph hadi imago mpaka awe amekomaa kingono (Foelix, 1996). Wakati buibui anapofikia hatua ya imago, yeye hubaki hapo hadi kifo chake. Buibui wengi huishi kwa mwaka mmoja tu, lakini wengine huishi kwa miaka miwili au zaidi, wakikaa katika maeneo yenye ulinzi (buibui wa kila mwaka wanaingia ndani ya nyumba wakati wa vuli kwa sababu ya kutafuta mahali pazuri pa joto pa kukaa wakati wa majira ya baridi kali). Buibui huzaana kwa kuweka mayai katika vifungo vya hariri vinavyoitwa mifuko ya mayai. Buibui hutumia desturi za kuchumbiana (hasa katika buibui wanaosonga kwa macho) ili kuruhusu kiume kukaribia karibu na mwanamke bila kuamsha majibu ya kuwinda. Kwa kuzingatia kwamba ishara za kukaribia zinabadilishwa kwa usahihi, buibui wa kiume lazima aondoke kwa wakati baada ya kuchumbiana ili kutoroka kabla ya vichocheo vya kawaida vya wawindaji vya jike kuanza kufanya kazi tena. Uhamisho wa shahawa ni mchakato usio wa moja kwa moja. Mbwa-mwitu anapokuwa tayari kuoa, yeye hutengeneza kitambaa cha kuunganisha mayai ambacho chachwa hutolewa. Kisha anaingiza vipande vyake vidogo vya mwili (vinavyoitwa pia 'palpi'), vipande vidogo vinavyofanana na miguu kwenye sehemu ya mbele ya kichwa chake, ndani ya shahawa, na kuichukua kwa kuvutia kwa njia ya mishipa ya damu. Buibui wa kiume mwenye umri wa miaka miwili na zaidi huwa na vifuniko vilivyoinuka kwenye ncha ya vidole vyao kwa ajili ya kusudi hili, na hii ni njia muhimu ya kutambua jinsia ya buibui katika shamba. Akiwa na vidole vyake 'vimejazwa' hivyo, yeye huenda kutafuta jike. Mwili wa kiume huingia kwenye sehemu ya uzazi ya mwanamke, inayoitwa epigyne. Yeye huhamisha shahawa yake ndani ya mwanamke kwa kupanua sinusi katika kiwiko chake. Utendaji wa kawaida wa buibui wa jamii ya Tidarina ni kwamba, kabla ya kukomaa, mwanaume huondoa moja ya vidole vyake na kuingia katika maisha yake ya watu wazima akiwa na kidole kimoja tu. Pipi ni asilimia 20 ya uzito wa mwili wake, na kwa kuwa uzito huo huzuia sana mwendo wake, buibui huondoa moja kati ya pembe hizo mbili ili aweze kusonga. Katika spishi ya Yemeni Tidarren argo, palp iliyobaki kisha huvunjwa na mwanamke. Pembe hiyo iliyojitenga hubaki kwenye kiwiko cha mwanamke kwa muda wa saa nne hivi na inaonekana inaendelea kufanya kazi kwa kujitegemea. Wakati huohuo, jike hula jike asiye na hisia. "Jarida la Zoolojia, 2549-459 (Cambridge University Press, DOI 10.1017 S0953899-1000) ""Kama ilivyoelezwa hapo juu, ni moja ya vitabu vya kisasa zaidi katika historia ya zoolojia."