Yeah, worms go deep into the ground and seek shady spots this time of year to protect themselves from the heat. If they can't go deep of get to a shady spot they'll expire.
On the bright side though, that mass of rotting worm flesh would be a great base for a catfish stink bait!... if you could stand the stench yourself.
Lots of great people on this site and G-3 is one of them.