Q.lawn deterioration
My lawn is eaten away by something (insect/pesticides). Small soil heaps are formed after watering my lawn. Also, little holes in the ground. I could not detect any insect or ant. Please help.
I would not rule our rodents as a possible problem.
If this is killing your lawn you may want to bring in a professional to examine the damage.
Here are some links that may help you pinpoint the issue.
https://www.gardeningknowhow.com/lawn-care/lgen/grass-fungus.htm
https://www.gardeningknowhow.com/plant-problems/pests/animals/vole-control.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/diatomaceous-earth-insect-control.htm