This blog post describes “millions (literally) of tiny sphere-like objects bouncing around on the ground” in Davis, California. Sort of like jumping beans, these plant byproducts are pretty weird but have a natural cause.
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.
I’ve never seen anything like. No one had including people who had lived in Davis for decades.
Upon inquiring what they might be, they discovered the answer, a jumping oak gall fallen from the tree. From this entry on leaf galls:
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.
The article continues:
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.
Really cool stuff!