If you don't like spiders then you probably wouldn't like this either: from China come reports of what's claimed to be the largest known aquatic insect. (I can't find any actual published scientific descriptions of the creature; it will be nice to see the claim confirmed – or denied! – as it's a pretty impressive specimen.
My first thought on seeing this image was, a dobsonfly! I've not ever seen an adult specimen, but the aquatic larvae I encountered when running a macroinvertebrate lab class (way back in my Massey days) have equally impressive mandibles – hence the nickname of 'toe biters'. Given that the adult Megalopteran pictured here has a 21cm wingspan (!), I wouldn't care to encounter its larvae when paddling in a stream.
Becky Crew has a great take on this creature on her Running Ponies blog, including some fascinating info on other giants of the insect world.