Well it was a swimming pool, someone would had to have put jellyfish in it.
I actually saw very little evidence of spiders and other nature-wants-you-dead type animals while I was there. Didn't see any spiders at all in fact, just two webs but they've got a lot of (harmless) ants in Palm Cove. Deaths from sharks, spider bites and what not are apparently quite rare, though shark attacks have been on the icnrease on the south-weat coast.
It also seems like the majority of Australia's wildlife is lying dead on the side of the road.