OK, here's the little insect I found on the leaf.

The insect is an aphid.

The damage looks like hail damage from a while ago.

Yes, it is some sort of mechanical damage and aphids can't chew leaves.

Really, mechanical damage? I guess that is good news, if that's what it is. We don't really get a lot of hail around here, so that's surprising. We just moved into this house about a month ago though, so maybe something happened before we moved in that I don't know about. And I didn't think that aphids were quite as mobile as this little insect is. He moves sideways really fast. OK, well thanks for the input!

3 choices... insect... disease ... mechanical ...

so they have ruled out two ... and do understand mechanical does NOT necessarily mean a machine ...

i have had such damage on hosta.. not only from hail... but also twigs falling out of a carp tree in a wind storm.. acorn bombing.. etc ...

when gravity is involved.. its called mechanical ...

ken

ps: any insane squirrel building a nest above???

There IS actually a large maple tree above it. There are other plants nearby (including a huge hosta) which don't have similar damage, but it does look like only the older leaves on the hydrangea were affected, so maybe some branches fell during a wind storm before the hosta sprouted this year, for example. I never would have thought of mechanical damage, and my nearby garden center didn't know was this was, so I appreciate that Garden Web came through. Thanks! And I never realized there were fast-moving aphids. I've only ever seen slow/motionless ones. But it doesn't seem like there are too many of them on the hydrangea anyway, luckily.