Sounds like squirrels!

The phrase: "Some small twigs with a bunch of leaves each. Plunk!" makes me think of twig girdlers or twig pruners. My driveway is littered right now with small twigs holding green leaves from a large Cedar elm tree. There is more than one kind of insect that causes this. It makes a mess to rake up, but they don't do serious damage to the health of the tree.

From the internet: "Damage is most often seen in late summer, fall or winter. A twig girdler female adult chews a V-shaped groove around a twig, girdling it. She then deposits eggs, and the worm-like larvae develop within the outer portion of the twig beyond the girdling cut. Winds eventually break twigs at the cut. Among twig pruners, on the other hand, it is the larvae that make the most damaging cut. Twig pruner female adults deposit eggs near a twig tip, and larvae tunnel inside the branch toward its base. When larvae are full-grown, they cut through all the wood at one place inside the twig, leaving only the outer bark intact. The branch eventually breaks at that point."

Here is a link that might be useful: More about the twig girdler ...

Roselee, I think you got it. I was wrong. It isn't the crepe myrtle at all. It's cedar elm! There is a crepe myrtle under a big cedar elm and now that I look at them carefully, the leaves of the two look quick-glance similar, especially in the twilight, when I was looking at them. Of course, they are not. I was fooled. In fact, it should have been pretty obvious because the number of leaves on the ground couldn't have come from one 20-foot crepe myrtle. In fact, looking on the web, cedar elm seems to be a favorite target for these girdlers.

The "small twigs" I'm referring to are ones with up to a dozen leaves. Probably a little small for squirrels to be bothering with.

Looking way up at the cedar elm branches, it looks like a pretty happy tree. I have seen no sign of the bugs, but I guess the damage is not from big bugs, but from newly hatched larvae. Now, I have a number of cedar elms around my lot, and those others show no sign of this damage.

I think the most important thing is that the clear consensus is that the tree is not at risk, and there is nothing that needs to be done about it (except rake up leaves). That's easy!

There, I fixed the subject line!

"The "small twigs" I'm referring to are ones with up to a dozen leaves." Exactly, with some as few as five or six leaves. My driveway is covered! I've seen it before, but never this many. The conditions for proliferation of whatever insect it is must have been near perfect this year.

Of course, what is surprising about this is that it isn't leaves themselves that are dropping. Every leaf on the ground is attached to a few other leaves with a small stem.

Also, this is fall elm flower/seed time, so all that mess is mixed with fallen seed pods.

I've never seen this before, so it's kind of remarkable. Indeed, it must be a special year for twig girdlers. Well, really, the larvae were laid last year, so it was really last year that was good for them. I gather that the reason they're pretty harmless is that the larvae are feeding on the twigs that drop, and not on the tree itself.

Now, it seems from the link below, girdlers generally attack thicker branches than what I'm seeing. Maybe they've done that, but those larger branches just haven't fallen yet?

Here is a link that might be useful: Twig Girdler- TAMU

This is the third pile of green twigs off the cedar elm tree mixed with seeds and a few dead leaves that I've swept up just off the driveway in the last few weeks. The other piles were higher and almost filled our large trash can. The tree itself is still thickly leafed. There's been a few fallen green twigs before, but never in this number.

That's exactly what I'm seeing. It just doesn't stop! Remarkably, the Cedar Elm tree up above still looks pretty flush, even though a lot of it is on the ground in pieces. We've stopped parking the car in the driveway underneath for the last few weeks, because the debris just piles up on the car if you do.