Digger Bee is a common name for a group of fast flying, Ground Nesting Bees and Wasps all of different sizes, colors and shapes. Some Digger Bees visit a wide variety of flowers and are important in pollination. Cicada Killers hunt Cicadas, a large robust flying insect. Cicada killers use their stinger to paralyze their prey and bring back to the nest for their egg. Neither species is very aggressive but can be hard to control. All Digger Bees, Digger Wasps and Cicada Killers are Solitary Bees, meaning that they don't produce Bee Colonies as do Social Insects. Instead, individual Female Bees do all the work of rearing.
They all have Stingers and the Cicada Killer Sting is very painful but all Digger Bees are not very aggressive nor do they have the Hive Instinct to protect. Just about the only ways to get stung is if you handled one or accidentally stepped on one which is rare because of how fast flying they are. Pets may catch one and get stung but probably only once.
Signs will be very Fast Low Flying Bees usually the males in search of a chance to mate. This usually starts in the morning when the sun rises and starts to warm the soil. Other signs could be perfectly round hole in the lawn, planters and the edge of walkways. These holes look like a pencil was pushed into the soil and then pulled out. Cicada Killer Holes are much bigger, about the size of your index finger. There may be up to a pound or more of soil dug out. These Bees and Wasps will only be around for a few weeks. Unless they are treated, the following year will be worse since each Adult Digger Bee laid several eggs.
Your yard is probably well drained with light textured soil with full and warm sunlight. Your home probably has a lot of other Insects that these Bees and Wasps hunt or are near trees harboring Cicadas. You may have had a minor problem without realizing it for a couple of years until progressively getting worse.
Control of these Bees and Wasps need to be addressed when they are still in the nest, before the sun rises. Cicada Killers will dig quite deep so what ever Pesticide you used needs to be able to reach them and saturate them. With the wet sandy soil they prefer this could be a lot of Pesticide. To little and you will just anger them, to much and you may harm your grass. You need to know where your well is, where does the drainage flow to, is it close to fish and what other animal feed from your yard. These are just a few considerations.