Juvenile Long-horned Orb-weaver Spider (Macracantha arcuata)

Juvenile Long-horned Orb-weaver Spider (Macracantha arcuata) 
As members of the orb-weaver family of spiders, these amazing creatures build the typical circular web of their cousins across pathways.
The purpose of the disproportionately long body horns however remains a mystery, each horn is about 45mm in length. 

Generally, orb-weaving spiders are three-clawed builders of flat webs with sticky spiral capture silk. The building of a web is an engineering feat, begun when the spider floats a line on the wind to another surface. The spider secures the line and then drops another line from the center, making a "Y". The rest of the scaffolding follows with many radii of nonsticky silk being constructed before a final spiral of sticky capture silk. The third claw is used to walk on the nonsticky part of the web. Characteristically, the prey insect that blunders into the sticky lines is stunned by a quick bite, and then wrapped in silk. If the prey is a venomous insect, such as a wasp, wrapping may precede biting.

Reference:
http://en.wikipedia.org/wiki/Orb-weaver_spider
Photos by John Horstman