Five or so years ago, I started noticing these bulges in the stems of Mugwort/Artemesia vulgaris around Brooklyn. I thought they must be galls, formed probably by some kind of insect. Surprisingly, given how common they seemed, nobody on iNaturalist ventured a guess as to what was inducing the plant to bulge out.
Flash forward to last week. My old iNat observations started being identified as being caused by Pseudomordellina hattorii, a tumbling flower beetle. I did a little digging and found the source of this flurry: “First Record of a Gall-Inducing Mordellid in North America”: in the latest Transactions of the American Entomological Society. The beetle species was previously only known in Japan.
On Tuesday, I sliced up one of the galls from the many at the Park’s Department Mugwort Farm at Bush Terminal.
Here’s the grub, or larva, found inside. 5mm at this stage.
Backyard and Beyond 
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