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Most spiders' eyes can detect little more than brightness and motion, so vision plays only a minor role in behaviour. However some species, such as jumping spiders, wolf spiders, and deinopids, have more developed eyes which they use in hunting and courtship. [2]
The outer pair are "secondary eyes" and there are other pairs of secondary eyes on the sides and top of its head. [25] Eyes of the jumping spider, Plexippus paykulli. Spiders have primarily four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. [13]
Similar to those of other recluse spiders, their bites sometimes require medical attention. The brown recluse is one of three spiders in North America with dangerous venom, the others being the black widow and the Chilean recluse. Brown recluse spiders are usually between 6 and 20 millimetres (0.24 and 0.79 in), but may grow larger.
Most spiders possess venom, which is injected into prey (or defensively, when the spider feels threatened) through the fangs of the chelicerae. Male spiders have specialized pedipalps that are used to transfer sperm to the female during mating. Many species of spiders exhibit a great deal of sexual dimorphism. [1]
Spiders do not have compound eyes, but instead have several pairs of simple eyes with each pair adapted for a specific task or tasks. The principal and secondary eyes in spiders are arranged in four, or occasionally fewer, pairs. Only the principal eyes have moveable retinas. The secondary eyes have a reflector at the back of the eyes.
Bolas: Bolas spiders are unusual orb-weaver spiders that do not spin the webs. Instead, they hunt by using a sticky 'capture blob' of silk on the end of a line, known as a ' bolas '. By swinging the bolas at flying male moths or moth flies nearby, the spider may snag its prey rather like a fisherman snagging a fish on a hook.
Jumping spiders have four pairs of eyes; three secondary pairs that are fixed and a principal pair that is movable. The posterior median eyes are vestigial in many species, but in some primitive subfamilies, they are comparable in size with the other secondary eyes and help to detect motion. [10]
Sparassids are eight-eyed spiders. The eyes appear in two largely forward-facing rows of four on the anterior aspect of the prosoma. Many species grow very large – in Laos, male giant huntsman spiders (Heteropoda maxima) attain a legspan of 25–30 centimetres (9.8–11.8 in).