Everything GardeningRotoplast & Self Watering Planter Systems

We discovered a deep hole under a garden shrub. Yellow Jacket nest debris (cellular) was scattered in vicinity. Yellow Jackets were crawling in the hole. We have a considerable wildlife population on and around our 2 quiet acres. What would this digging animal be seeking?

We see rats crossing the garden but are afraid to use pesticides as we have a cat and would not want to harm her or other wildlife.
Any suggestions?