Nope you are talking about the Daddy Long Legs and that is just a myth anyhow and was disproven in 2004.
No no, not the daddy long legs, know that all too well and not only because I was bit by one once.
They look like spider mites, very small and in your face red.
But I guess it's just another myth as-well, can't see what such a small spider would use such toxic venom for.
About the sand spider, well how common is it ?