Ground Ivy (Also Creeping Charlie, Gill-Over-the-Ground) Glechoma hederacea
"You know that viney weed with the scalloped-edged leaves that takes over your yard? That one that you can tell is a long, climbing thing, but when you try to rip it out of your flower beds, just the part in your hands breaks off instead of pulling up the whole thing? The one that gets those pretty little purple flowers in the spring? Turns out Europeans brought it here on purpose, just like garlic mustard. It's a salad green. You can use it in soups. You can make tea out of it. The Saxons used to use it like hops in beer. It has medicinal properties. A 1986 study found it inhibits EBV and skin tumors. It's part of the mint family, and mints were traditionally used as all-purpose antibiotics." - gigglingwizard
I don't have much to add, except that it smells really nice when you mow it. It's a common urban and suburban plant, and first joined us as 365 urban species number 118
But what the hell is growing on it?! I was just sitting in my yard when I saw this thing. I assumed it was a small lawnmower's mushroom and went to pluck it--to my surprise I pulled out a plant with a foreign growth.
I knew that it had to be a gall, but had no idea that any creature made use of ground ivy for this purpose!
Ground Ivy Gall Wasp Liposthenes glechomae
I cut it open to see a single wormlike larva inside, very much like an oak apple gall
. Wormlike larvae are usually the babies of wasps or flies, two groups known to produce galls. At least mites and pathogens were eliminated as the causal agent. I searched the index of my copy of Tracks and Sign of Insects and Other Invertebrates
but ground ivy was not in the index, nor its scientific name. I posted pics here, on facebook, and on bugguide. One of the authors of the above book chimed in to identify the gall as belonging to Lisposthenes glechomae
, a tiny wasp in the same family as the one that causes oak apples. He also pointed out that this gall appears in his book (p. 395--it's in the index under galls, ground ivy).
The gall protects the developing larva from predation while providing a food source for it. The insect causes little to no damage to the plant. This wasp is native to Europe, and was translocated inadvertently with its host.