Lilac Leaf Munchers Revealed

Who munched this leaf?

Four years ago, being enamored of a leafcutter bee building a nursery in the railroad tie of a flower bed, I searched the yard looking for the source of her leaf-fragment chamber partitions. That’s when I discovered many lilac leaves with “munched” margins (1). Since lilacs are said to be a favorite of leafcutter bees, I concluded that leafcutters were the munchers, as I explained in a 2015 post.

This leafcutter bee carried the leaf fragment into the crack directly below her.

Was this the source? No!

But I was wrong, as I learned when the Smithsonian’s Paleobiology Department, part of the National Museum of Natural History in Washington, DC, contacted me. They want to use a photo from my blog—an image of “a scalloped leaf margin made by the black vine weevil”. I opened the image—there was my lilac leaf photo, the one at the top of the post! After doing some web research, I agreed the sculptors were black vine weevils, not leafcutter bees. But the story is interesting even so.

Black vine weevil (3). Photo by David Short (slightly cropped); source.

The Smithsonian is preparing a guidebook to “identification of invertebrate (principally insect), pathogen and environmental damage on compressed plant fossils”. They aim to include modern-day analogs as convincing evidence. For example, there are plant fossils that show scalloped leaf margins similar to those made by black vine weevils. My photo is a good modern analog—in fact, a “level 1 match”.  Perhaps these weevils have been adding their distinctive notches to leaf margins for a long time. I look forward to seeing the guidebook and the photos of scalloped fossil leaves … just how similar are they to the leaves in my yard?

The guidebook will be available free online—I don’t know when, but I’m to be notified. If so, I will definitely share!

Notes

(1) Thanks to Tina Huckabee for her recent discussion about tolerating “munched leaves” (c. halfway into the post). “A common fallacy is that there is something wrong with foliage that has been eaten …”

(2) For more about the wonderful leafcutter bees, with no assumptions as to the source of their partitions, see my 2014 leafcutter bee post.

(3) Adult black vine weevils are about a half inch long. They feed on leaves at night, dropping to the ground if disturbed (they can’t fly). While adults cause no serious injury to plants, the larvae—fat little legless white grubs with reddish-brown heads—live in the soil and may damage roots. More information here, including possible control measures.