Well, biting bugs are never a pleasant consideration and the first idea that springs to mind is the worst indeed but it is bedbugs (keep scrolling down to see similar pics):

http://www.bedbugsbites.net/what-do-bed-bugs-look-like-bed-bug-pictures/

They will bite all over but have been known to concentrate on ankles and some people react more (or are more tasty) than others.

Next idea is Chiggers:

https://en.wikipedia.org/wiki/Trombiculidae

And Biting Midges aka "Sandfly" in Australia (but you said yours only crawl):

https://en.wikipedia.org/wiki/Ceratopogonidae

Other things that bite ankles include mosquitos, ticks, and the already mentioned fleas. .

So, since you have a specimen (or maybe several) package it up and take to the South Australian Museum for an ID check:

https://www.samuseum.sa.gov.au/learn/discovery-centre

Our team knows all about our exhibits and can even help identify any specimens you bring in. If you do manage to stump them with a particularly tricky question, they have our expert scientists to call on to help find the answer.