 Spiders make use of a variety of different threat displays . Some such as Argiope and Pholcus make themselves and their webs vibrate rapidly when they are disturbed ; this blurs their outline and perhaps makes them look larger , as well as more difficult to locate precisely for an attack . Mygalomorphae spiders such as tarantulas exhibit deimatic behaviour ; when threatened , the spider rears back with its front legs and pedipalps spread and fangs bared . Some species , such as the dangerous Indian ornamental tree spider ( Poecilotheria regalis ) have bright colouring on the front legs and mouthparts which are shown off in its threat display when it " rears up on its hind legs , and brandishes the fore limbs and palpi in the air " . 
