Jumping oak gall swarm surprises Davis neighborhood

I was walking my dog Elvis with my daughter Julie on Sunday and as we have in the past, we came across something very science-y. (note you might enjoy my Scientist in the Garden series.)

At the dog park where Elvis likes to play and hunt for rodents in the nearby bushes, there were millions (literally) of tiny sphere-like objects bouncing around on the ground.

Jumping Jehoshaphat!

See video above.

The tiny balls bouncing all around us was like something out of a movie or invasion of the body snatchers.

These poppy seed-sized balls came in orange, yellow, and white versions. They were jumping around like crazy, collectively making an impressive “whoosh” sound.

What in the world? Others at the dog park were mystified too.

I’ve never seen anything like. No one had including people who had lived in Davis for decades.

Jumping Oak Gall
Jumping Oak Gall.

Julie and I were puzzled. A fellow dog walker went home and got her husband, who is an entomologist. He took some to study, but off hand did not know what they were.

I speculated to Julie that this little bouncing balls were like some miniaturized form of Mexican jumping bean.

A friend later told me that they jumping oak gall, a type of leaf gall. At one point in the video you can see a much larger “branch gall” of the kind that commonly plague oak trees in Davis and fall the ground, but which do not bounce around of their own accord.

I’d never heard of jumping oak gall, but apparently it is fairly rare.

Here’s the relevant part of the gall entry on the Davis Wiki:

In Davis, our Valley Oaks are commonly afflicted with jumping oak gall caused by a small cynipid wasp species (Neuroteras saltatorius). These are the tiny “jumping beans” you will notice falling on your picnic table under the big oak tree. These round pinhead-sized yellow or brown seed-like galls typically appear first on the leaves, falling off when the lone inhabitant is mature; the wasp’s activity makes the gall “jump” several inches off the ground. It is believed that the larvae hop around to locate a soil crack in which to hide and pupate before maturing to adulthood and chewing its way out of the gall. The wasps themselves are dark and so tiny that you’ll probably never see them — they are harmless to people.

So jumping oak gall is kind of like Mexican jumping beans, but the galls are very tiny. Still the jumping is amazing and must burn up huge amounts of energy. Inside each little gall is a wasp larva that is doing a wicked kind of dance.

The galls each form individually from the oak tree as a reaction to the presence of a wasp egg/larvae.

Hmm, wonder if this is a stem cell-dependent process in terms of the oak cell growth to form the gall? I had to ask, right?

What is in part so astounding about jumping oak gall is the massive expenditure of energy that goes into the jumping, especially relative to the size of the galls that are about 1mm in diameter. They “jump” about 3-5mm constantly, then out of the blue sometimes as much as an inch, and they jump frequently.

I’m curious where all that energy comes from.

I also wonder….Why have I never seen these in the 6 years I’ve been here? Is it like 7-year locust or something?

As it turns out, there are three big oak trees surrounding the dog park, which likely explains the abundance of the jumping galls in this particular place.

There’s an interesting video (below) on YouTube of a wasp emerging from a leaf gall.


3 thoughts on “Jumping oak gall swarm surprises Davis neighborhood”

  1. neato! Great report, thanks. I love learning stuff like this.

    A tantalizing taste of the ecosystem the valley oaks must’ve supported.

    A quibble, though. If the branch gall plagues the oaks, the jumping gall afflicts the trees: how so? Does wolf then plague the elk, moose afflict the pondweed? I wonder if that’s not a whiff of the old bug-killing entomology.

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