Sep 09, 2013 - 10:33 AM
Demon WP should work both ways. It works on direct contact, and it also has a residual effect. If scorpions are nesting and living inside a cement block retaining wall, then you need to figure out how to get the Demon WP inside of it.
Either spray the base and the top very thoroughly and also try to get down inside of it, or consider drilling some holes in between each void of the blocks (2 sides to each block) and then treat inside that way.
You could also use a duster such as the JT Eaton's Duster, and Delta Dust and dust inside of the holes you drill to treat inside the blocks. This way is a little more expensive and time consuming, but better than just spraying the outside of the wall and crossing your fingers.