The upper image formed during a pullaway phase of my finger's proximity.
The Spiders in the photo below were formed under conditions different from those of the experiment which produced the pattern in the upper image.
In this experiment the layered condition of the surface was fiberglass dust on top of field-dust. After power was turned off, downward bursts occured to create small raised features which grew as material gathered back to the discharge point but most of the material initially clung to my finger until I cleaned it off back onto the screen..