Spiders pump their legs with blood and farm silk factories
Order Araneae ranks seventh among all organism orders for species richness, blanketing every continent but Antarctica with hunters and weavers. Eight limbs, fang-tipped chelicerae, and spinnerets define air-breathing arachnids that extend legs hydraulically because they lack extensor muscles entirely.
A spider's body runs on unusual engineering. Its segments are fused into two parts linked by a slim waist, the pedicel, which lets the abdomen swing freely while spinning silk. It has no antennae, and in all but the primitive Mesothelae every ganglion is merged into one mass, the most centralized nervous system of any arthropod. Lacking extensor muscles, it straightens its legs with blood pressure. Some breathe with two pairs of book lungs, while most araneomorphs have turned the rear pair into tracheae. Spiders can swallow only liquid, and bristly beards on the jaws strain out solid bits.
Silk comes from spinnerets fed by as many as six kinds of glands. The spiral orb web may be among the oldest designs, yet tangled cobweb builders are now more numerous and varied. Silk-spinning relatives lacking spinnerets lived 386 million years ago, and the first true spiders appear in Carboniferous rocks dated between 318 and 299 million years old.
Almost every species hunts; only Bagheera kiplingi, described in 2008, is known to feed mainly on plants. Together some 25 million tonnes of spiders eat 400 to 800 million tonnes of prey a year, catching it with sticky webs, swinging bolas, disguise or pursuit. Most sense vibrations, but active hunters see sharply, and Portia jumping spiders appear to plan their tactics. Males court elaborately to avoid being eaten by larger females, and a few social species share webs holding up to 50,000 animals.
Taxonomists had recorded 53,680 species in 139 families by January 2026. The name itself comes from a Germanic word meaning spinner, and researchers now test their venom as medicine and their silk genes in plants and mammals.
Source: Spider
