The unit of electric field strength is V/m. They put ants inside a test apparatus, so the "per meter" part is fixed (by its design) and the voltage is experimentally manipulated. They do use the right units elsewhere in the paper.
I imagine this was done to avoid measuring the electric field in the electrode/air/floor/ant medium, which is not exactly homogeneous.
The unit of electric field strength is V/m. They put ants inside a test apparatus, so the "per meter" part is fixed (by its design) and the voltage is experimentally manipulated. They do use the right units elsewhere in the paper.
I imagine this was done to avoid measuring the electric field in the electrode/air/floor/ant medium, which is not exactly homogeneous.