Well I won't go hunt down all the details, but from what I've heard...
Australia has something like 7 of the most deadly creatures in the World. Not sure how that happened. But different Websites don't seem to agree on what ones are or are not.
As for size, well I think that RUSSIA, CANADA, and USA for land mass would each swallow Australia as well. Not shaped well to show it but by dimensions they're each much larger.
As for population the top 3 are: China, India, USA
List of countries by population
This list shows Australia 6th in rank
List of countries and outlying territories by total area
.