I couldn't see the picture very well but it looks to me like a flea beetle. They are hard to get rid of so you'll have to keep after them if it's a large infestation.

Neem oil is an environmentally friendly product that is good for many pests including flea beetle. Neem oil is made from the nuts of the neem tree

There are other products out there that will work too to keep them under control

Thanks, downlinggram. I pulled up some pictures and they look similar. Mine don't seem to jump, though, as the websites said flea beetles could. I had one trapped for quite a while taking a picture of it, and it could climb and run quickly, but it never jumped. Neem oil might work on whatever kind of beetle it is, though.

It actually looks more like good bug to me. Plant tarnish bugs and four lined plant bugs will both attack astilbe. Maybe your bug is eating something you can't easily see very well.

Interesting, Patty--its ladybug-like appearance did make me wonder if there was something else hiding in the astilbe blossoms. Looks like neem works against tarnished plant bug too so maybe I'll try it and see if it stops the damage?

Not flea beetle.
Instead, a carpet beetle. The adults visit flowers to eat pollen. Other than that, they don't eat plant tissues.

Thanks, jean. If it's a carpet beetle, could it be eating the whole flower? I have some other astilbes (not pictured) that have not a single flower on them anymore--just stalks (like the tops of the flowers in pictures 3 & 4).

...and are they going to come eat my carpets when they're done with the flowers?

I think the beetle is innocent too. You might want to try taking a look at the plant after dark. Not everything is sleeping at night and maybe there's something like an asiaic beetle or two chewing on it after dark.... Although I think they would target the leaves as well.

Is your beetle covered with short hairs. If it is a carpet beetle they don't eat plants but do eat dead bugs. It appears their biggest damage is if they enter your home where they lay eggs that consume natural fibers such as cotton and leather ect. Either way I really doubt he's eat your flowers. He's kinda cute.

I just went outside with a flashlight and found the REAL culprit!!! The flowers were covered with asiatic beetles!! kato_b, thanks for figuring it out, and thanks to the rest of you for helping exonerate the other little beetles!

Now...what do I do about it? My most vigorous astilbe is yet to fully bloom and I'd love to save it before it gets eaten.

asiatic beetles are a pain, sorry to hear you have them.
I didn't want to spray anything so I ended up going out there with a pail of soapy water, picking them off and dropping them in the water to drown. It's a bit on the strange side to be out there in the dark going over your plants with a flashlight, but..... the neighbors will talk and there's always that awkward run in with an evening dog walker, but it seemed to control them enough.
I heard someone suggest Surround, which is a clay based spray that's supposed to work... there are plenty of other sprays with chemicals that should work too but I've never gotten that serious about control. Maybe someone else has better ideas.

asiatic beetles are a pain, sorry to hear you have them.
I didn't want to spray anything so I ended up going out there with a pail of soapy water, picking them off and dropping them in the water to drown. It's a bit on the strange side to be out there in the dark going over your plants with a flashlight, but..... the neighbors will talk and there's always that awkward run in with an evening dog walker, but it seemed to control them enough.
I heard someone suggest Surround, which is a clay based spray that's supposed to work... there are plenty of other sprays with chemicals that should work too but I've never gotten that serious about control. Maybe someone else has better ideas.