Spiny Spiders, sometimes known as Jewel Spiders or Christmas Spiders are members of the orb weaver group of spiders.
They are relatively small spiders, reaching a maximum total body length of only around 12 mm for females, and 5 mm for males. They feed on small flying insects that get entangled in their webs. They are harmless to humans, though the webs can be a nuisance for bushwalkers. They are predominantly a shiny black, with variable white, yellow, and orange patterns.
Information from: https://en.wikipedia.org/wiki/Austracantha
Spiny Spiders often build their webs in aggregations or groups. They also have the distinction of being the only spider to deliberately make its support thread visible to other animals (see top picture). It is thought that this is to prevent larger animals from inadvertently walking into the webs and damaging them.
They are most abundant during the summer months hence the name of ‘Christmas Spiders’.