So how do those larger roaches get inside your house and on your patios to your yards, you know, the black ones that scurry along? They’re sewer roaches or otherwise noted as oriental roaches. They live in the sewer systems and storm drains. If you listen closely, you can hear the water running through the storm drains. During a dry spell, that water will dry out. The roaches will look for more moisture and exit through this hole here and scurry across the pavement over to your yard where there's lots of rock to hide underneath.
Furthermore, the plants all have little water drippers on them which keep the ground underneath the plants by the roots moist, perfect environment. Often times these roaches are found in tropical areas and that environment is tropical. Eventually it gets real hot out here and this rock turns to about two hundred degrees, during real strong heat waves the roaches will exit the yard and actually search for cool surfaces. So, they end up overflowing from the yard into the foundation of your house where you will often find gaps on your foundation like the gap you see there. Cool air exits the building that way because you are actually air-conditioning your house, sucks the insect population into your walls, and then you feel the pressure.