Garden: Something is eating my birch tree leaves?

[Nerys53]

Something is eating my birch tree leaves? Many leaves have little round holes and like someone took a crafts scissors and cut lacy edges of leaves like old pictures have a deckled edge.
I did not see any creatures on/under the leaves. We had several heatwaves this summer and now it is september and temps are 27C. Any idea what this might be?
I use the birch leaves for foot baths for OA and use only those that are hole-free which is like 1/3 of it.

[RandallS]

I did not see any creatures on/under the leaves. We had several heatwaves this summer and now it is september and temps are 27C. Any idea what this might be?

Where are you? Your use of Celsius tells me "probably not the US" but that doesn't narrow it down much. 

[LadyBug]

Something is eating my birch tree leaves? Many leaves have little round holes and like someone took a crafts scissors and cut lacy edges of leaves like old pictures have a deckled edge.
I did not see any creatures on/under the leaves. We had several heatwaves this summer and now it is september and temps are 27C. Any idea what this might be?
I use the birch leaves for foot baths for OA and use only those that are hole-free which is like 1/3 of it.

27C is Too Hot for September.

Also is there any sticky white residue on the leaves that are most affected? Does your area have high concentrations of moths? Are there any natural pest predators in your area(like red ladybugs or spiders)? If yes to the last one look into what attracts them, if you can bring some to your area you might be able to use them to keep pests in check

[Altair]

Something is eating my birch tree leaves? Many leaves have little round holes and like someone took a crafts scissors and cut lacy edges of leaves like old pictures have a deckled edge.
I did not see any creatures on/under the leaves. We had several heatwaves this summer and now it is september and temps are 27C. Any idea what this might be?
I use the birch leaves for foot baths for OA and use only those that are hole-free which is like 1/3 of it.

I was going to say leaf cutter bees, but in my experience (1) birch is not one of their favored species, and (2) they leave one or two big perfect circles, not a lace pattern. Maybe birch leaf miners?

https://homeguides.sfgate.com/guide-birch-tree-pests-diseases-47674.html