Every 17 years theses cicada emerge in huge numbers. They litter the ground, cover vegetation and drown out most other noise with their song. They are Brood X. (Springfield, VA)
This is some of the first visible evidence of a cicada emerging. It has built a tunnel to the surface and here it is using mud to construct a wall or chimney to protect the tunnel from water or sand getting in. It comes up from the depths of the tunnel with a load of mud, positions the mud, then goes back down for more. The cicada will use this chimney as a protected look out. Once it feels safe the cicada will leave the tunnel and work its way upward to find a suitable place to molt.
This video is speeded up about 300%.
A mix of shed larva exoskeletons and cicadas in various stages of emergence pile up under my oak tree.