I had the same problem, crickets turning a darker color, laying on there backs ect. UNTIL I started to use the light bulb and if the room got to cold I used a heater in that room. 80 degrees is not even hot for them...They love the heat. One thing. Take the dying and dead out asap, they produce (release)a chemical and you will lose more. For my breeding tanks that raise the egg into babies I use a heating pad underneath with lights and room heater.