Spiders are air breathing arthropods
They also have over 100 different varieties. 
They are the largest order of arachnids
They say that the daddy long legs has one of the most potent venoms, however it is harmless to humans because it's pincers are too brittle to pierce human skin.
Unlike most arthropods, spiders have no extensor muscles in their limbs 
The tensile strength of a spider's web can hold over 200x it's own weight.
Unlike insects, spiders do not have antennae
Spider's are nature's most buildworthy predator.