Way back on June 18 we did a Neighborhood Nature blog post about Hackberry Nipple Galls, which you can read here. On this morning’s walk I found two Hackberry trees with half a dozen or more Yellow-rumped Warblers in them, hunting for bugs to eat. That got me thinking that maybe some of the bugs they were eating had grown up inside Nipple Galls. The warblers wouldn’t let me get close enough to see what they were eating, so instead I found some Hackberry leaves with lots of galls on them and took them home to dissect.
Before I picked them, the leaves looked like this — covered with nipple-shaped growths, called galls, that grew when insects called Psyllids (SILL-lids) laid their eggs on the leaves:
These Hackberry leaves are covered with Nipple Galls. The galls formed when insects, called Psyllids, laid their eggs on the leaves. The gall became a nursery for the baby Psyllids, which fed on the insides of the gall. The gall provided shelter and food at the same time.
After I cut open one of the galls on our kitchen table, it looked like this:
The cut-open nipple gall had a tiny Psyllid insect inside a hollowed-out cavity.
I cut open a few more galls, and more tiny Psyllids crawled out. They were about as big as the head of a straight pin:
The pinhead-sized Psyllid on the lower left was walking around, but the Psyllid on the upper right was upside down. You can tell these Psyllids are not yet fully grown, because they don't have wings. They just have "wing buds" behind the head, which will become wings after they shed their skins another time or two.
So, maybe the warblers were eating adult Psyllids that had emerged from galls on the Hackberry trees, or maybe they were eating something else. But what I really want to know is if any birds peck open Nipple Galls to catch the not-yet-fully grown Psyllids. (I’ve seen Downy Woodpeckers break into Goldenrod Galls, but those galls are somewhat larger.) I guess I’ll have to keep a close eye on any birds I see in Hackberry trees this fall. I’ll also search through Hackberry leaves for galls dissected by bird beaks instead of knives.
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Update added two days later (October 22, 2009): Rather than throw the gall-covered Hackberry leaves outside, we put them in a container with a lid and waited to see if adult Psyllids would emerge. When we opened the container this morning, this is what we found:
There were at least four of these winged adult Psyllids in the container with the gall-covered Hackberry leaves. (Because of the wings, they were twice as long as a pinhead is wide.)
Now, doesn’t that look like a good snack for a warbler?
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You can read more about Psyllids and Nipple Galls here and here and here.
