No crocs in southwest Australia. There are many poisonous snakes but they're really not a worry - more scared of you than you are of them. Wear boots and long socks if you're concerned. A lot of poisonous spiders, too, but just shake your boots out before you put them on and you'll be right. The real danger is heat, lack of water and remoteness. Hiking in summer is extremely ill-advised.

The big thru-hike track in SW Australia is the Bibbulmun Track: https://www.bibbulmuntrack.org.au/