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Arachnids are an insect-like group that consists of scorpions, mites, ticks, spiders (obviously), and their cousins.
Arachnids have exoskeletons, which is an exterior shell-like skin, arachnids have this instead of a real skeleton. All arachnids have four legs in adulthood, do not have antenna nor wings, and most have their bodies separated into two sections: cephalothorax and abdomen.
Silk proteins, made up of amino acid chains, are produced by glands inside the spider, the proteins are then pushed out through long ducts into the microscopic spigots in the spider's spinnerets. Each spigot has a valve that can control the thickness and speed of the fibers. As the twisted together fibroin protein molecules are pushed out of the ducts, they hit the air and become a strand of silk.
Most spiders have multible silk glands, each one creating a different type of silk for different purposes. Having a large selection of silk varieties, the spider can spin them together, having a large variety of fiber material to make.
For one, the silk is used for webs, but since the spider can have different types of silk, the spider uses a stronger, more sturdy, type of silk to create the base of the web, then uses a stickier, thinner formula for the webbing weaving around the web skeleton to catch prey. The second use is for wrapping around the prey once caught in the web and paralyzed with the spider venom.
The two main parts of the spider body are the cephalothorax and abdomen. The cephalothorax is essentially the head, it is the front part of the spider body, it is where the eyes are located and mouth, along with the spiders’ chelicerae (venom distributors) and coxae of the legs are (the connection of legs to the spiders’ body).
The second part of the spider is the abdomen, the behind-half of the spider. The abdomen is about twice as big is the cephalothorax, and is were the spinnerets are located.
All spiders are born with eight legs, and surprisingly, those lags have many different parts to them, seven, to be exact. The parts are: coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus.
Most spiders have eight eyes, but some species have six, four, and even two.
Spiders today can’t grow to be larger than about the size of a fist, with the exception of the goliath spider, who can grow up to one foot in body length. If you think this is big, then you haven’t heard of the megarachne servinei, the half-meter long spider ancestor. This ancestor was alive 300 million years ago, and research has shown that that was the largest size spiders have been throughout history.
There is not much facts on ancestors in creating venom, researchers come to the conclusion that venom was part of the evolution process along with silk-making capabilities.
It was found that most spider ancestors were more crab-like, with the addition of some not even being able to weave silk. As some of these crustacean-like ancestors were not born with silk-weaving spinnerets, there were also many ancestors after their era with silk weaving capabilities. The uses of the ancestors’ silk were uses more for protecting eggs, though, as time passed, researchers figure that spiders needed to conserve energy, in order to catch prey easily, spiders then learned to create webs.