Sunday, August 20, 2023

Hackberry Nipple Galls

I visited our neighbor's big hackberry tree which stands 65 feet tall.  Several of its lower branches are 4" in diameter and are covered with hackberry nipple galls.  There are no galls on the higher branches or on the other side of the tree.  While these galls are not uncommon, I had never seen them so prolific.

The galls are actually scar tissue produced by the leaf in response to a tiny psyllid insect larva chewing on the leaf.  This tissue grows around the larva, protecting it while it goes through five successive instars before reaching maturity.  The winged adults emerge in the fall and overwinter, mostly in the cracks in the hackberry bark, before mating and laying eggs, starting the annual cycle again.

I cut open several of the galls and found tiny larvae.  The one in this video which I filmed with a hand-held digital microscope turned around in its cavity repeatedly, confused by the sight of a human looking in its home.  When I knocked it out onto the cutting board, it scurried around faster that I could follow it.  You can see here that my larva was the size of a comma in the New York Times!

There are between 7-13 species in the US, all traditionally called a single species, Pachtpsylla celtidismamma.  


Home sweet home

The shape of their galls vary. "Some are like rounded cones or disks, some are like indented mushroom caps, some are like pudgy doughnuts, some are knobby like nipples; and the nipple galls may be hairy or glabrous (smooth). One type makes inflated, blister-like pouches within the leaf."

Adult on a window screen - MD

These insects do not cause any significant harm to the tree.  The MDC Discover Nature site mentions that the winged adults may cover a window screen.  Under magnification they resemble a microscopic cicada.  You can see the first graduates of this years class of galls in this video.

These tiny psyllids (aka. jumping plant lice) are in the same suborder as aphids, scale insects, mealybugs, whiteflies, and the phylloxera insects.  You would never know they exist unless you stumble across a hackberry tree that is hosting them over their summer vacation, hanging out in the sun.

More pictures are at this OzarkBill link.