Can it get to hot for butterflies? Yes.
Just like being to cold for butterflies, it can get to hot for them as well. Most butterflies are active when it is 65 to 85 degrees. However, when temps hit 90 or higher, butterflies seek shade. It is known that some butterflies can die if it gets to hot.
Here in Mid-Michigan this past week and all this week, 90 degrees will not be uncommon.
This past weekend was a good example of slower than normal butterfly activity. A morning at Rose Lake WMA normally produces many butterflies of a nice variety. Sunday morning (until about 10:30am) butterflies were minimal at best, with 12 species seen and less than 30 individuals counted.
So, if you are out on a hot day and not seeing any butterflies, or very few, they are most likely seeking a cooler place.