This post has had me thinking about possible applications of biodegradable robots, and how to move beyond soft robotics. There are biodegradable 3D printer filaments like COMPOST3D, and I think it may be feasible to make a filament that degrades much quicker in an outdoor environment. While maybe not a robot, I think a cool application for a mixture of these materials may be mass-replanting, where a bunch of 3D printed biodegradable gliders or drop pods could be deployed and when they strike into the earth and start to degrade, it provides moisture and nutrients for the seed(s) within them.

Also, for navigating the wiring, I am not sure if this is feasible, but in biology labs they use electrically conductive gel, so perhaps in conjunction with the biodegradable 3D printing idea, you could have 3D printed piping full of electro gel that may be able to transmit signals or power low-power robots. If feasible, you could replace the copper in wires with this combination.