Spiders are creepy, crawly, annoying little buggers, who taxinomical name is Arachnid. Although they may appear to be insects, arachnids actually have eight legs, whereas insects only have six legs. Spiders can spin silk-like webbing, which they use to ensnare prey and some species may also carry venom, some of which is strong enough to even be fatal to humans.
One particular spider played a brief yet highly pivotal role in the life of a nerdy teenager named Peter Parker. While visiting a science laboratory, Pete was bitten by a radioactive spider. The arachnid died soon after, but the venom bite imbued Parker with the prorportionate strength, speed and reflexes of a spider. Gifted with these fantastic abilities, Peter Parker donned a red and blue costume and became the wall-crawling web-head the world knows as Spider-Man.
On Lost Girl there exists a race of Fae spider whose venom turns people psychotic. A Fae succubus named Bo and her partner Kenzi were both infected by such a creature, which increased their inherent paranoia and self esteem, driving them to fight one another. 
- Teen Wolf: Said the Spider to the Fly - Spiders come out of the mouth of a victim.
- Teen Wolf: Triggers - Spiders come out the mouth of the corpse of Edgar.