What kinds of plants are they? Are the holes on the edge of the leaf or more in the middle?

The plants are mostly flowering plants like roses, Blackeyed susan, prim roses and Dhalia (flower edges are eaten up). The holes are mostly on the edge and few in the middle.

Any number of chewing insects could be causing the problem - leaf cutter bees on the roses, earwigs on the dahlias, various larvae of flying insects that typically show up as some sort of caterpillar. Many of these are nocturnal in habit, feeding by night and hiding away, sometimes underground, in the heat of the day, safe from predators. Generally, the damage they do is minimal and is primarily cosmetic - I personally don't mind sharing my roses with leaf cutter bees :-) Earwigs can be bothersome, but are relatively easy to trap using a rolled up section of newspaper, moistened, and placed at the base of plants they favor. They will hide in this dark, damp location at night and it can be collected and disposed of in the morning. If populations of caterpillar-like larvae are high and are doing significant damage, you might want to consider some sort of control, preferrably organic in nature. Avoid using chemical pesticides as they will kill off beneficials as well and your garden is already telling you the ecosystem is out of balance.

Sometimes it is best to let nature take its course - birds and other predators will typically take care of the problem and plants are seldom seriously damaged by a few holes in the leaves.

Thanks for the info and tips.

I have 2 olympic asian pear trees whose leaves have become covered in irregularly shaped holes that have brown edges around edges of holes. What could this be..!?

Thank you!